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					1.    Some substances dissolve in water.

      The solubility of a substance is the number of grams that will dissolve in 100 grams of water.

      The diagram below shows how the solubilities of two substances, potassium nitrate and sodium
      chloride, vary between 0 – 100°C.

                   250                                                                            potassium
                                                                                                  nitrate


                   200




                   150
      Solubility
       (grams)

                   100




                    50
                                                                                                  sodium
                                                                                                  chloride

                     0
                         0   10   20    30     40    50    60     70       80        90      100

                                             Temperature (°C)

      (a)   How much potassium nitrate dissolves in 100 grams of water at 60°C?

                                                                 ........................................ grams
                                                                                                                  (1)




Bryngwyn School                                                                                                    1
      (b)   Describe what happens to the solubilities of potassium nitrate and sodium chloride
            between 0 – 100°C.

            Answer in as much detail as you can.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (5)
                                                                                                                                               (Total 6 marks)



2.    (a)   The diagram shows one way of making crystals of copper sulphate.

                                                             Filter




            Sulphuric
              acid
                                                                                                Crystallise
                     Copper
                      oxide                  Heat
                                                                Copper sulphate                                          Copper sulphate
                                                                   solution                                                 crystals

            (i)       Why was the solution filtered?

                      ..........................................................................................................................
                                                                                                                                                           (1)

            (ii)      How could you make the crystals form faster from the copper sulphate solution?

                      ..........................................................................................................................
                                                                                                                                                           (1)




Bryngwyn School                                                                                                                                             2
            (iii)     The chemical equation is shown for this reaction.

                                        CuO(s) + H2SO4(aq)  CuSO4(aq) + H2O(l)

                      In the chemical equation what does (aq) mean?

                      ..........................................................................................................................
                                                                                                                                                           (1)

      (b)   Blue copper sulphate crystals go white when warmed. How could you use the white
            copper sulphate as a test for water?

       Blue copper sulphate                                                                                                         White copper
             crystals                                                                                                                sulphate
                                                       Warm                                      After warming

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                           (2)
                                                                                                                                               (Total 5 marks)



3.    Rainwater falling on limestone rocks can form caves.




                                                                                        Rain



                                                             Limestone
                                   Cave
                                                                   Lake




Bryngwyn School                                                                                                                                             3
      (a)   Complete the sentences by choosing the correct words from the box.

                                   acidic                                   alkaline                                    dissolves

             hard                                       reacts                                   soft                                             tastes

            You may use each word once or not at all.

            Rainwater is an ....................... solution which ....................... with limestone. The

            solution formed in the lake is known as ....................... water. One advantage of

            drinking the water from the lake is that it ....................... better than rainwater.
                                                                                                                                                           (4)

      (b)   Samples of water were tested by shaking with soap solution. The results are shown in the
            table.

                                                                             Volume of soap solution to
                              Water sample (50 cm3)
                                                                               form a lather in cm3

                                        lake                                                     15

                                        boiled lake                                               3

                                        rain                                                      1


            (i)     What is seen when only 10 cm3 of soap solution is shaken with 50 cm3 of water
                    from the lake?

                    ...........................................................................................................................
                                                                                                                                                           (1)

            (ii)    Why did the rainwater need only 1 cm3 of soap solution to form a lather?

                    ...........................................................................................................................
                                                                                                                                                           (1)

            (iii)   Why did the water from the lake need 15 cm3 of soap solution to form a lather?

                    ...........................................................................................................................
                                                                                                                                                           (1)

            (iv)    Explain why boiled water from the lake needed only 3 cm3 of soap solution to form
                    a lather.

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                        (2)
                                                                                                                                            (Total 9 marks)



Bryngwyn School                                                                                                                                             4
4.    A titration was used to find the concentration of the sulphuric acid solution in the beaker.



                                                         Beaker



                                                    Sulphuric acid
                                                       solution




                                                                                                                                    Solution of
                                                                                                                                     an alkali



                                                                                                                                    X




                                             Pipette

                                             Flask                                                                                 Flask



                                              Sulphuric acid                                                                        Sulphuric acid
                                                 solution                                                                              solution
                                                                                                                                          +
                                                                                                                                      indicator
               Stage 1                                                                              Stage 2

      Stage 1 25.0 cm3 of the sulphuric acid solution was added to a flask using a pipette.

      Stage 2 A solution of an alkali was added to the acid until the solution was neutral.
              The volume of the alkali was noted.

      (a)   What would be the pH of the sulphuric acid solution?

            .....................................................................................................................................
                                                                                                                                                     (1)




Bryngwyn School                                                                                                                                       5
      (b)   Why was a pipette used instead of a measuring cylinder in Stage 1?

            .....................................................................................................................................
                                                                                                                                                           (1)

      (c)   Name the apparatus labelled X which is used to add the alkali in Stage 2.

            .....................................................................................................................................
                                                                                                                                                           (1)

      (d)   Name an alkali that could be used in Stage 2.

            .....................................................................................................................................
                                                                                                                                                           (1)

      (e)   (i)       Name an indicator that you could use to find out when the solution was neutral.

                      ...........................................................................................................................
                                                                                                                                                           (1)

            (ii)      How would you know that the solution was neutral?

                      ...........................................................................................................................
                                                                                                                                                           (1)
                                                                                                                                               (Total 6 marks)



5.    Washing powders are a mixture of substances. The substances in a box of Kleenkwik washing
      powder are shown.




                                                                                            Detergent
                                                                                            Bleach
                                                                                            Perfume
                                                                                            Soap
                                                                                            Sodium phosphate




                                                Supersoap


      (a)   Which substance in the washing powder gives clothes a pleasant smell?

            ....................................................................................................................................
                                                                                                                                                           (1)

      (b)   What does a bleach do?

            ....................................................................................................................................
                                                                                                                                                           (1)




Bryngwyn School                                                                                                                                             6
      (c)       Sodium phosphate removes the hardness in water.

                (i)       What is hard water?

                          .........................................................................................................................

                          .........................................................................................................................
                                                                                                                                                               (1)

                (ii)      Why should the hardness be removed?

                          .........................................................................................................................

                          .........................................................................................................................
                                                                                                                                                               (1)

                (iii)     Give another method which removes the hardness in water.

                          .........................................................................................................................

                          .........................................................................................................................
                                                                                                                                                               (1)

      (d)       Circle the chemical which is used to make detergents.

                          carbonic acid                      hydrochloric acid                      sulphuric acid
                                                                                                                                                               (1)
                                                                                                                                                   (Total 6 marks)



6.    A leaflet listed the effects of hard water:

                                  HOW HARD WATER COSTS YOU HARD CASH

               Hard water causes:

                Blocked showers, burnt out immersion heaters

                Scale build up inside water pipes

                Higher water heating cost

                Extra soap required to get a lather

      Describe how softening the hard water could save money.

      ...............................................................................................................................................

      ...............................................................................................................................................

      ...............................................................................................................................................
                                                                                                                                                               (3)
                                                                                                                                                   (Total 3 marks)




Bryngwyn School                                                                                                                                                 7
7.    The graph shows the mass of copper sulphate which dissolves in 100 g of water at different
      temperatures.

                                      80




                            60
             Solubility of
            copper sulphate
             in grams per
              100 grams
                            40
               of water



                                      20




                                        0
                                            0                 20           40           60           80                                         100
                                                                   Temperature in degrees Celsius (°C)

      (a)    A saturated solution of copper sulphate was made using 100 g of water at 60°C.

             Use the graph to answer the following questions.

             (i)       What mass of copper sulphate dissolves at 60°C?

                                                                                        Mass = ............................................ g
                                                                                                                                                            (1)

             (ii)      What mass of copper sulphate would come out of this solution if the temperature
                       goes down from 60°C to 30°C?

                       ...........................................................................................................................

                       ...........................................................................................................................

                                                                                        Mass = ............................................ g
                                                                                                                                                            (2)

      (b)    Suggest why it is not possible to measure the solubility of substances in water at
             temperatures above 100°C or below 0°C.

             .....................................................................................................................................

             .....................................................................................................................................
                                                                                                                                                            (1)
                                                                                                                                                (Total 4 marks)




Bryngwyn School                                                                                                                                              8
8.    (a)   Complete each sentence about water by choosing the correct words from the box. Each
            word may be used once or not at all.

                   calcium              chloride                 chlorine                hydroxide                 nitrate            oxygen

            (i)       Hardness in water is caused by dissolved ........................................ ions.
                                                                                                                                                   (1)

            (ii)      Some ........................................ dissolved in water is essential for aquatic life.
                                                                                                                                                   (1)

            (iii)     The use of artificial fertilisers can result in many natural waters being

                      contaminated with dissolved ........................................ ions, which can have

                      harmful effects on babies.
                                                                                                                                                   (1)

      (b)   The diagram shows part of the water cycle.


                                                                            Wind                  Sun
                                                   Cloud

                                                            Rain


                                                                  Lake

                                                                                                                     Sea
                                                                       River




            Describe what is happening in the water cycle.

            To gain full marks you should write down your ideas in good English. Put them into a
            sensible order and use correct scientific words.

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                   (3)




Bryngwyn School                                                                                                                                     9
      (c)   This label has been taken from a bottle of carbonated mineral water.


              Sparkling Mineral Water                                                                 MINERAL ANALYSIS
                                                                                                       TYPICAL VALUES mg/l

                                                                                                  Calcium                              35.0
                                                                                                  Magnesium                             5.3
                                                                                                  Sodium                               22.0
                                                                                                  Potassium                             2.2
                                                                                                  Chloride                             38.0
                                                                                                  Sulphate                             22.0
                                                                                                  Nitrate                              34.0
                                                                                                  Fluoride             LESS THAN 0.1


                   Carbonated Natural Mineral Water                                                           2 LITRE         e
            (i)    The bar chart shows the amounts of some of the ions in this mineral water.

                                40




                                30


               Amount
               of ions in 20
              mg per litre



                                10




                                  0
                                         Calcium               Sodium             Chloride             Sulphate              Nitrate

                   Complete the bar chart to show the amount of nitrate ions given on the label.
                                                                                                                                                       (1)

            (ii)   Describe how water is carbonated.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................
                                                                                                                                                       (2)
                                                                                                                                           (Total 9 marks)




Bryngwyn School                                                                                                                                        10
9.    This label was on a bottle of lemonade.



                                                                   AQA Brand



                                          Ingredients: carbonated water, citric acid,
                                             sweeteners, preservative, flavouring


      (a)   Carbonated water is made by dissolving a gas in water.

            Draw a ring around the name of this gas.

            carbon monoxide                          carbon dioxide                        hydrogen                     oxygen
                                                                                                                                                           (1)

      (b)   Complete the sentence by crossing out the two words that are wrong.

            To make as much of this gas as possible dissolve in water, the temperature

                                     high                                                         high
              should be                           and the pressure should be                                   .
                                     low                                                          low
                                                                                                                                                           (1)

      (c)   Choose one substance from the other ingredients on the label that produces hydrogen ions
            (H+(aq)) when dissolved in water.

            .....................................................................................................................................
                                                                                                                                                           (1)
                                                                                                                                               (Total 3 marks)




Bryngwyn School                                                                                                                                            11
10.   A chemist used a titration to investigate a solution used to unblock drains.




                                                       ’
                                                   A ‘X
                                                 AQ
                                                 LIQUID
                                                 DRAIN
                                                 OPENER
                                                  tough on blocks



      25 cm3 of a diluted solution of Drain Opener was put into a beaker. The graph shows how the
      pH of this solution changed as hydrochloric acid was slowly added.

                         14

                         13

                         12

                           11

                         10

                           9

                           8
                      pH
                           7

                           6

                           5

                           4

                           3

                           2

                           1

                           0
                                0   5    10   15     20    25     30    35               40      45
                                        Volume of hydrochloric acid in cm 3

      (a)   What volume of hydrochloric acid was needed to neutralise the Drain Opener solution?

                                                      Volume = ...............................................cm3
                                                                                                                    (1)




Bryngwyn School                                                                                                     12
      (b)   Which of the following best describes Drain Opener solution?

            Draw a ring around your answer.

             neutral                strong acid                strong alkali                  weak acid                 weak alkali
                                                                                                                                                           (1)

      (c)   Which of the following would be best for accurately measuring the volume of
            hydrochloric acid added?

            Draw a ring around your answer.

            beaker                        burette                      measuring cylinder                                 pipette

            Give a reason for your choice.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (2)
                                                                                                                                               (Total 4 marks)



11.   A student wanted to find out how much of a substance, to the nearest 0.1 gram, dissolves in
      15cm³ of water. His plan for the experiment is shown below, but the descriptions of some of the
      steps have been missed out.

                                1 Grind the substance in a pestle and mortar.

                                2

                                3

                               4 Add the 0.1 gram of the substance to the water in the test tube.

                                5

                               6 Examine to see if all the substance is dissolved.
                     YES
                                  NO
                               7

      The missing steps in his plan are written below, but not in the correct order.

            A         Shake thoroughly for some time.

            B         Measure out 0.1 gram of the substance.

            C         Record the amount of substance added.

            D         Measure out 15cm³ of water into a test tube.

Bryngwyn School                                                                                                                                            13
      (a)   Write the letters A, B, C and D in the boxes in his plan, in the correct order.
                                                                                                                                                           (4)

      (b)   How would you know that the substance had dissolved?

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (2)
                                                                                                                                               (Total 6 marks)



12.   The label shows the ions present in the bottle of spring water. This water is temporarily hard.



                                                                                       Composition mg/litre
                                                                       calcium Ca2+                                                   35
                                                                       magnesium Mg 2+                                                15
                                                                       potassium K +                                                   1
                    SPRING                                             sodium Na+                                                     12
                    WATER                                                           –
                                                                       chloride Cl                                                    10
                                                                       fluoride F –                                                    1
                                                                       nitrate NO3 –                                                   2
                                                                       sulphate SO4 2–                                                 6
                      WITH
                      FIZZ                                             hydrogencarbonate HCO 3 –                                     179


      (a)   Name the compound that would be present in the greatest amount if this water were
            evaporated to dryness.

            .....................................................................................................................................
                                                                                                                                                           (2)

      (b)   (i)       What is hard water?

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                           (2)

            (ii)      State one advantage of hard water.

                      ...........................................................................................................................
                                                                                                                                                           (1)




Bryngwyn School                                                                                                                                            14
      (c)   Describe an experiment that would show that this water is temporarily hard.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                          (4)

      (d)   This hard water may be softened as shown.

                            2+               2+
                        Ca and Mg
                          in water




                                                     Na +                                                     Ca 2+ and Mg2+
                                                   on solid                                                     in solid




                                                                                         Na +
                                                                                      in water

                            Before                                                      After

            What name is given to this process?

            .....................................................................................................................................
                                                                                                                                                          (1)
                                                                                                                                             (Total 10 marks)




Bryngwyn School                                                                                                                                           15
13.   The chemical compositions of two samples of hard water, A and B, are shown in the table.

                                                                       Sample A                       Sample B

                                  pH                                          9                              8
                                  Ions present:                          Concentration in mg/litre

                                            Ca 2+                           101                            135
                                            Mg 2+                               2                              9
                                             Na +                               9                              6
                                          HCO 3–                            299                                6

                                             Cl –                             14                               8

                                            SO 4 2–                             5                          136
                                            NO 3–                               6                              0

      (a)   What does the pH value tell you about these samples?

            .....................................................................................................................................
                                                                                                                                                    (2)

      (b)   Use the information in the table to explain what is meant by hard water.

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                    (1)

      (c)   What would be the effect of using temporarily hard water in a kettle?

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                    (2)

      (d)   (i)       Explain which sample of water is permanently hard.

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                    (3)




Bryngwyn School                                                                                                                                     16
            (ii)      How could this hardness be removed?

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                                               (1)

      (e)   State one advantage of drinking hard water.

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                                               (1)
                                                                                                                                                                  (Total 10 marks)



14.   This label has been taken from a bottle of mineral water.

      Use the information on the label to answer some of the questions which follow.

                   CARBONATED NATURAL                                                                   Official Analysis
                      SPRING WATER                                                                            mg/l                                         mg/l
                                                                                    Calcium ...........58                        Sulphate ...........26
                                                                                    Magnesium ......17                           Nitrate ..........<0.1
                                                                                    Potassium ..........2                        Iron ....................0
                                                                                    Sodium ............22                        Aluminium.......00
                                                                                    Bicarbonate ....238                          Dry residue
                                                                                    Chloride ...........40                       at 180°C ........285

                                                                                                        pH at Source...7.3
                                                                                         Filtered through ancient limestone
                                                                                         to a depth of 1700 metres, this water
                                                                                         supplies a natural balance of minerals.



                                                                                                        SPRING
                                                                                                                   UPPER                  OW
                                                                                              GRITS &                                   FL
                                                                                                                 LIMESTONE
                                                                                              SHALES                               VA
                                                                                                                                 LA
                                                                                                                            NT                   LOWER
                                                                                                 GEOLOGICAL           CIE                      LIMESTONE
                                                                                                   FAULT            AN


                       SPAR K LIN G
                                                                                                              500 ml

      (a)   This mineral water is hard.

            (i)       Name an ion from the label which makes this mineral water hard.

                      ..........................................................................................................................
                                                                                                                                                                               (1)

            (ii)      Describe and give the results of a test to show that this mineral water is hard.

                      ..........................................................................................................................

                      ..........................................................................................................................

                      ..........................................................................................................................
                                                                                                                                                                               (2)




Bryngwyn School                                                                                                                                                                17
      (b)   Describe some of the advantages and disadvantages of hard water.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (3)
                                                                                                                                               (Total 6 marks)



15.   Many soft drinks contain citric acid.




                                                                                          INGREDIENTS: CARBONATED
                                                                                          WATER, SUGAR, CITRIC ACID,
                                                                                          ACIDITY REGULATOR (E331),
                                                                                          FLAVOURINGS,
                                                                                          PRESERVATIVE (E211)



      (a)   Citric acid is a weak acid.

            (i)       What is meant by a weak acid in terms of its ionisation in water?

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                           (1)

            (ii)      Describe and give the results of an experiment which would show that citric acid is
                      a weaker acid than hydrochloric acid of the same concentration.

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                           (2)




Bryngwyn School                                                                                                                                            18
      (b)   Citric acid behaves as an acid. Explain why, using the ideas of Arrhenius and of
            Bronsted-Lowry.

            To gain full marks in this question you should write your ideas in good English. Put them
            into a sensible order and use the correct scientific words.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (3)
                                                                                                                                               (Total 6 marks)



16.   This information has been taken from two bottles of Australian spring water.


            Ridgway Spring Water comes                                                Homeland Spring Water originates
            from a natural source deep under                                          from a high mountainous source in
            the Central Highlands of Victoria.                                        the Central Highlands of Victoria..


                       TYPICAL ANALYSIS                                                           TYPICAL ANALYSIS
                          (mg per litre)                                                             (mg per litre)

            hydrogencarbonate                                158                       hydrogencarbonate                                158
            chloride                                          33                       chloride                                          27
            sodium                                            33                       sodium                                            24
            calcium                                           30                       magnesium                                         15
            magnesium                                         23                       calcium                                           12
            potassium                                          9                       potassium                                          5



      (a)   The labels show the names of the ions present in Ridgway and Homeland spring waters.

            Describe how these ions got into the water.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (2)




Bryngwyn School                                                                                                                                            19
      (b)   Both Ridgway and Homeland spring waters are hard.

            (i)     There are two ions shown on the labels which make these spring waters hard.

                    Name one of these ions.

                    ...........................................................................................................................
                                                                                                                                                        (1)

            (ii)    Ridgway spring water is about twice as hard as Homeland spring water.

                    Use the information on the labels to explain why.

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                        (2)

            (iii)   Describe how you could use soap solution to show that Ridgway spring water is
                    about twice as hard as Homeland spring water. You should state how the
                    experiment is made fair.

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                        (3)
                                                                                                                                            (Total 8 marks)



17.   The following passage is about the preparation of lead iodide, an insoluble salt.

                     An excess of potassium iodide in solution was shaken with some
                     lead nitrate solution in a test tube.

                     The lead iodide precipitate was separated from the mixture and
                     then washed several times with water.

                     The lead iodide was dried and then placed in a bottle.




Bryngwyn School                                                                                                                                         20
      (a)   Suggest a reason why excess potassium iodide was used.

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (1)

      (b)   What word used in the passage shows that lead iodide is insoluble?

            ....................................................................................................................................
                                                                                                                                                           (1)

      (c)   Suggest how lead iodide can be separated from the mixture.

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                           (1)

      (d)   Why was the lead iodide washed with water?

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                           (1)

      (e)   Suggest a method which could be used to dry this lead iodide.

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                           (1)

      (f)   Lead compounds are toxic.

            Suggest a suitable safety precaution that should be taken when using toxic substances in
            laboratories.

            ....................................................................................................................................
                                                                                                                                                           (1)
                                                                                                                                               (Total 6 marks)




Bryngwyn School                                                                                                                                            21
18.   Soft drinks, such as this Cream Soda, contain weak acids.




      (a)   Lactic acid is a weak acid.

            (i)     Complete this sentence about lactic acid by crossing out the two words in the box
                    that are wrong.

                                                                            atoms
                    Solutions of weak acids contain fewer hydrogen          ions      than strong acids of
                                                                          molecules

                    the same concentration.
                                                                                                             (1)

            (ii)    Which one of the following could be the pH of a solution of a weak acid?
                    Draw a ring around your answer.


                             1            5            9             13

                                                                                                             (1)

            (iii)   Which one of the following shows the colour of universal indicator when it is
                    added to a weak acid?

                    Draw a ring around your answer.


                             blue         green        orange         red
                                                                                                             (1)


Bryngwyn School                                                                                              22
            (iv)   You are given solutions of lactic acid and hydrochloric acid, which have the same
                   concentrations.

                   Describe how you could use some magnesium ribbon to show that lactic acid is a
                   weaker acid than the hydrochloric acid.

                   State how you would make it a fair test.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................
                                                                                                                                                       (3)

      (b)   This Cream Soda contains carbonated water.

            Which one of the following substances is dissolved in water to carbonate it?

            Draw a ring around your answer.

            calcium carbonate                       carbon                 carbon dioxide                         carbon monoxide
                                                                                                                                                       (1)

      (c)   Which acid-base theory states that – acids are proton donors?

            Place a tick ( ) next to the name of the theory.

                                     Name of theory                      Tick (         )
                               Brønsted and Lowry
                               Dalton
                               Haber
                               Mendeleev
                                                                                                                                                       (1)
                                                                                                                                           (Total 8 marks)




Bryngwyn School                                                                                                                                        23
19.   The information in the box is about the preparation of copper sulphate crystals.

            Step 1:        Add a small amount of black copper oxide to some hot dilute sulphuric
                           acid, and stir.
            Step 2:        Keep adding copper oxide until it is in excess.
            Step 3:        Remove the excess copper oxide to leave blue copper sulphate solution.
            Step 4:        Evaporate the copper sulphate solution until it is saturated.
            Step 5:        Leave the saturated solution of copper sulphate to cool. Blue copper
                           sulphate crystals form on cooling.
            Step 6:        Remove the crystals from the solution remaining.
            Step 7:        Dry the blue crystals on a piece of filter paper.

      (a)   (i)     Suggest a reason for using excess copper oxide in Step 2.

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                  (1)

            (ii)    Suggest how the excess copper oxide can be removed from the solution in Step 3.

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                  (1)

            (iii)   What is meant by the term saturated solution?

                    ...........................................................................................................................

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                  (2)

            (iv)    Why do crystals form when a hot saturated solution cools?

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                  (1)

            (v)     Suggest why the blue crystals are dried in Step 7 using filter paper instead of by
                    heating.

                    ...........................................................................................................................

                    ...........................................................................................................................
                                                                                                                                                  (1)




Bryngwyn School                                                                                                                                   24
      (b)   The graph shows how the solubility of copper sulphate changes with temperature.

                              80




                              60



            Solubility in
            g per 100 g 40
              of water


                              20




                                0
                                    0                   20                 40          60                             80                 100
                                                                          Temperature in ºC

            Use the graph to answer the following questions.

            (i)    What is the solubility of copper sulphate at 80 ºC?

                                                      Solubility = .................................... g per 100 g of water
                                                                                                                                                       (1)

            (ii)   What mass of copper sulphate would be formed if a saturated solution of copper
                   sulphate, in 100 g of water, was cooled from 80 ºC to 20 ºC?

                   ...........................................................................................................................

                   ...........................................................................................................................

                                                                                                        Mass = ....................... g
                                                                                                                                                       (2)
                                                                                                                                           (Total 9 marks)




Bryngwyn School                                                                                                                                        25
20.   The diagram shows a simplified flow diagram of a water treatment works which supplies
      drinking water.

                                            Water from
                                             reservoir
                                                                                        Simplified flow diagram
                                                                                           of water treatment


                   Filtration
                                                                                       Sampling



                                          Chlorination
                                                                                                                       To homes
                                        and stabilisation
                                                                                          Storage

      (a)   Explain the purpose of:

            (i)    filtration

                   ...........................................................................................................................

                   ...........................................................................................................................

            (ii)   chlorination.

                   ...........................................................................................................................

                   ...........................................................................................................................
                                                                                                                                                 (2)
      (b)   Samples of the treated water must be tested at regular intervals.

            (i)    Suggest why.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................
                                                                                                                                                 (2)

            (ii)   Suggest how the use of ICT and/or data logging equipment could help with this
                   testing.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................
                                                                                                                                                 (2)


Bryngwyn School                                                                                                                                  26
      (c)   Drinking water can also be produced using distillation.

            Explain why this process is expensive.

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                    (1)

      (d)   In some parts of the country the water supplied to homes is hard water.

            (i)       Name one ion that can make water hard.

                      ...........................................................................................................................
                                                                                                                                                    (1)

            (ii)      Explain how hard water can affect central heating systems.

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                    (2)




Bryngwyn School                                                                                                                                     27
            (iii)     State one advantage of hard water.

                      ...........................................................................................................................
                                                                                                                                                          (1)
                                                                                                                                             (Total 11 marks)



21.   The salt sodium hydrogen phosphate (Na2HPO4) is used as a softening agent in
      processed cheese.




      It can be made by reacting phosphoric acid (H3PO4) with an alkali.

      (a)   Complete the name of an alkali that could react with phosphoric acid to make sodium
            hydrogen phosphate.

                                                   ....................................... hydroxide
                                                                                                                                                          (1)

      (b)   What is the name given to a reaction in which an acid reacts with an alkali to make a salt?

            .....................................................................................................................................
                                                                                                                                                          (1)

      (c)   How would the pH change when alkali is added to the phosphoric acid solution?

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                          (1)

      (d)   What ions are present when any acid is dissolved in water?

            .....................................................................................................................................
                                                                                                                                                          (1)

      (e)   What ions are present when any alkali is dissolved in water?

            .....................................................................................................................................
                                                                                                                                                          (1)




Bryngwyn School                                                                                                                                           28
      (f)    Write a chemical equation for the reaction which takes place between the ions you have
             named in (e) and (f).

             .....................................................................................................................................
                                                                                                                                                            (1)
                                                                                                                                                (Total 6 marks)



22.   (a)    This label has been taken from a packet of Andrews Antacid.

                                                                           ®
                     Andrews
                                                                                          When your stomach produces more acid
                                                                                          than it can cope with, symptoms can strike
                                                                                          in different ways.
                                                                                          Andrews Antacid tablets neutralise excess
                                                                                          acid and give fast and effective relief from

                     Antacid                                                              all 3 kinds of indigestion - heartburn, acid
                                                                                          indigestion and trapped wind.
                                                                                          DOSAGE: Adults - suck or chew 1 to 2
                                                                                          tablets as required.
            FAST EFFECTIVE RELIEF FROM                                                    Not recommended for children
            3 KINDS OF INDIGESTION                                                        Do not exceed 12 tablets in 24 hours.
                                                                                          If symptoms persist consult your doctor.
                                                                                          Store below 25ºC in a dry place.
            HEARTBURN                                                                                  Active ingredients:
            ACID INDIGESTION                                                                   Calcium Carbonate           600mg,
                                                                                               Magnesium Carbonate          125mg
            TRAPPED WIND
                                                                                                     STERLING                 GUILDFORD,
                                                                                                                              SURREY
            DISPERSE IN THE MOUTH                                                                    HEALTH                   PL 0071/0321


             (i)       Write the simplest ionic equation which represents a neutralisation reaction.

                       ...........................................................................................................................
                                                                                                                                                            (1)

             (ii)      Chewing the tablet cures indigestion faster than swallowing the tablet whole.
                       Explain why.

                       ...........................................................................................................................

                       ...........................................................................................................................
                                                                                                                                                            (1)

             (iii)     Write the formula of the magnesium compound present in Andrews Antacid.
                       You may find the Data Sheet helpful.

                       ...........................................................................................................................
                                                                                                                                                            (1)




Bryngwyn School                                                                                                                                             29
      (b)     The active ingredients in the Antacid react with hydrochloric acid in the stomach to give
              salts, water and carbon dioxide.

              A student investigated how quickly the tablets react with excess hydrochloric acid.

              40 cm³ of dilute hydrochloric acid were placed in a conical flask. The flask was placed on
              a direct reading balance. Two Antacid tablets were quickly added to the flask. The
              apparatus was weighed immediately. At the same time, a stop clock was started. The mass
              was recorded every half minute for 5 minutes.

              The results are shown in the table below.

            Mass of flask
            + contents (g)         92.0 90.0 89.0                   88.3 87.8            87.5       87.3 87.1 87.0                   87.0 87.0

            Time (minutes)            0        0.5        1.0        1.5       2.0        2.5        3.0        3.5        4.0        4.5       5.0


              The main active ingredient in Andrews Antacid is calcium carbonate.

              (i)     Balance the equation which represents the reaction between calcium carbonate and
                      hydrochloric acid.

                      CaCO3(s) + .......... HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g)
                                                                                                                                                      (1)

              (ii)    State the meaning of the symbol “(aq)”.

                      ...........................................................................................................................
                                                                                                                                                      (1)

              (iii)   Why does the mass of the flask and contents decrease?

                      ...........................................................................................................................
                                                                                                                                                      (1)




Bryngwyn School                                                                                                                                       30
      (c)   (i)    Plot the results on the graph below and draw a smooth curve to show how the mass
                   of the flask and its contents changes with time. Label this curve “A”.




                                                                                                              (3)

            (ii)   One of the results does not appear to fit the pattern. Circle this result on the graph.
                                                                                                              (1)

      (d)   The student did a second experiment. The only change was that the acid was twice as
            concentrated.

            On the graph, sketch a second curve to show a possible result for this experiment. Label
            this curve “B”.
                                                                                                              (2)
                                                                                                 (Total 12 marks)




Bryngwyn School                                                                                               31
23.    (a)   The reaction on mixing solutions of sodium hydroxide and hydrochloric acid is shown.

                                                     NaOH + HCl  NaCl + H2O

             Write the balanced ionic equation for this reaction.

             ....................................................................................................................................
                                                                                                                                                    (2)

       (b)   Varying amounts of sodium hydroxide solution and hydrochloric acid were mixed, but the
             total volume of the mixture was always 50 cm3. The temperatures of the solutions before
             and after mixing were recorded. A graph of the results is shown.



               30
      Temperature
       rise in °C




               20




               10
                       0                10                 20                30                 40                50 Volume of sodium
                                                                                                                     hydroxide in cm3

                      50                40                 30                20                 10                 0      Volume of hydrochloric
                                                                                                                          acid in cm3

             (i)       What was the highest temperature rise?

                       ..........................................................................................................................
                                                                                                                                                    (1)

             (ii)      Explain how the highest temperature rise shows that the sodium hydroxide solution
                       has a higher concentration than the hydrochloric acid solution.

                       ..........................................................................................................................

                       ..........................................................................................................................

                       ..........................................................................................................................

                       ..........................................................................................................................

                       ..........................................................................................................................
                                                                                                                                                    (2)

Bryngwyn School                                                                                                                                     32
      (c)   Calculate the concentration in mol/dm3 of a solution that was made by dissolving 100 g of
            sodium hydroxide and making the solution up to 1.0 dm3.

            Relative atomic masses: H 1; O 16; Na 23.

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

                                     Concentration of sodium hydroxide solution = ................... mol/dm3
                                                                                                                                                          (3)

      (d)   Calculate the total mass of sodium chloride that can be made from 100 g of sodium
            hydroxide.

            Relative atomic masses: H 1; O 16; Na 23; Cl 35.5.

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

                                                                                Mass of sodium chloride = ................... g
                                                                                                                                                          (3)

      (e)   Sodium can be made from the electrolysis of molten sodium chloride. Explain why
            sodium and molten sodium chloride conduct electricity in different ways.

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                          (2)
                                                                                                                                             (Total 13 marks)



24.   A student carried out a titration to find the concentration of a solution of sulphuric acid. 25.0
      cm3 of the sulphuric acid solution was neutralised exactly by 34.0 cm3 of a potassium hydroxide
      solution of concentration 2.0 mol/dm3. The equation for the reaction is:

                                     2KOH(aq) + H2SO4(aq)  K2SO4(aq) + 2H2O(l)



Bryngwyn School                                                                                                                                           33
      (a)   Describe the experimental procedure for the titration carried out by the student.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (4)

      (b)   Calculate the number of moles of potassium hydroxide used.

            .....................................................................................................................................

                                                                           Number of moles = .......................................
                                                                                                                                                           (2)

      (c)   Calculate the concentration of the sulphuric acid in mol/dm3.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

                                                                       Concentration = .................................. mol/dm3
                                                                                                                                                           (3)
                                                                                                                                               (Total 9 marks)




Bryngwyn School                                                                                                                                            34
25.   An oven cleaner solution contained sodium hydroxide. A 25.0 cm3 sample of the oven cleaner
      solution was placed in a flask. The sample was titrated with hydrochloric acid containing
      73 g/dm3 of hydrogen chloride, HCI.

      (a)   Describe how this titration is carried out.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (3)

      (b)   Calculate the concentration of the hydrochloric acid in mol/dm3.

            Relative atomic masses: H 1; Cl 35.5

            .....................................................................................................................................

                                                                                Answer = ................................... mol/dm3
                                                                                                                                                           (2)

      (c)   10.0 cm3 of hydrochloric acid were required to neutralise the 25.0 cm3 of oven cleaner
            solution.

            (i)       Calculate the number of moles of hydrochloric acid reacting.

                      ...........................................................................................................................

                                                                                 Answer = .......................................... mol
                                                                                                                                                           (2)

            (ii)      Calculate the concentration of sodium hydroxide in the oven cleaner solution in
                      mol/dm3.

                      ...........................................................................................................................

                                                                                Answer = ................................... mol/dm3
                                                                                                                                                           (2)
                                                                                                                                               (Total 9 marks)




Bryngwyn School                                                                                                                                            35
26.   An electric current was passed through dilute sulphuric acid. The apparatus used is shown.
      Oxygen was formed at the anode.




                                                                                        Dilute sulphuric
                                                                                              acid




                                             +                                   –

      (a)   What name is given to solutions which decompose when electricity is passed through
            them?

            .....................................................................................................................................
                                                                                                                                                           (1)

      (b)   The ionic equation for the reaction at the anode is:

                                                          4OH–  2H2O + O2 + 4e–

            Explain this type of reaction.

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (2)

      (c)   Write a balanced ionic equation for the reaction at the cathode.

            .....................................................................................................................................
                                                                                                                                                           (2)

      (d)   What happens to the concentration of the sulphuric acid as the electricity is passed
            through it? Explain your answer.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (3)
                                                                                                                                               (Total 8 marks)




Bryngwyn School                                                                                                                                            36
27.   A student carried out a titration to find the concentration of a solution of hydrochloric acid. The
      following paragraph was taken from the student’s notebook.

            I filled a burette with hydrochloric acid. 25.0 cm3 of 0.40 mol/dm3 potassium hydroxide
            was added to a flask. 5 drops of indicator were added. I added the acid to the flask until
            the indicator changed colour. The volume of acid used was 35.0 cm3.

      (a)   What piece of apparatus would be used to measure 25.0 cm3 of the potassium hydroxide
            solution?

            .....................................................................................................................................
                                                                                                                                                           (1)

      (b)   Name a suitable indicator that could be used.

            .....................................................................................................................................
                                                                                                                                                           (1)

      (c)   Calculate the number of moles of potassium hydroxide used.

            .....................................................................................................................................

            .....................................................................................................................................

                                          Moles of potassium hydroxide = ............................................ mol
                                                                                                                                                           (2)

      (d)   Calculate the concentration of the hydrochloric acid. The equation for the reaction is:

                                                         KOH + HCl  KCl + H2O

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

                               Concentration of hydrochloric acid = ........................................ mol/dm3
                                                                                                                                                           (2)
                                                                                                                                               (Total 6 marks)



28.   A sample of water taken from a lake was found to contain sulphuric acid.
      A student carried out a titration to find the concentration of the sulphuric acid in this sample.
      25.0 cm3 of the sulphuric acid solution was neutralised exactly by 34.0 cm3 of a potassium
      hydroxide solution of concentration 0.2 mol dm–3. The equation for the reaction is:

                                    2KOH(aq) + H2SO4(aq)  K2SO4(aq) + 2H2O(1)




Bryngwyn School                                                                                                                                            37
      (a)   Describe the experimental procedure for the titration carried out by the student.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (4)

      (b)   Calculate the number of moles of potassium hydroxide used.

            .....................................................................................................................................

                                                                                       Number of moles = ...........................
                                                                                                                                                           (2)

      (c)   Calculate the concentration of the sulphuric acid in mole per cubic decimetre (mol dm–3).

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................

                                                                                     Concentration = .................. mol dm–3
                                                                                                                                                           (3)
                                                                                                                                               (Total 9 marks)




Bryngwyn School                                                                                                                                            38
29.   (a)   This label has been taken from a bottle of vinegar.



                                                        es or preserva
                                                  dditiv               tive
                                               noa                          s

                                  MALT
                                VINEGAR                   Pur
                                                             eM         alt Vinega
                                                                                  r



            Vinegar is used for seasoning foods. It is a solution of ethanoic acid in water.

            In an experiment, it was found that the ethanoic acid present in a 15.000 cm3.sample of
            vinegar was neutralised by 45.000cm3 of sodium hydroxide solution, of concentration
            0.20 moles per cubic decimetre (moles per litre).

            The equation which represents this reaction is

                               CH3COOH + NaOH                                    CH3COONa + H2O

            Calculate the concentration of the ethanoic acid in this vinegar:

            (i)    in moles per cubic decimetre (moles per litre);

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                                       Concentration =................................... moles per cubic decimetre
                                                                                                                                                 (2)

            (ii)   in grams per cubic decimetre (grams per litre).

                   Relative atomic masses: H = 1; C = 12; O = 16.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                                       Concentration = .................................. grams per cubic decimetre
                                                                                                                                                 (2)

Bryngwyn School                                                                                                                                  39
      (b)   The flow diagram shows some reactions of ethanoic acid.

                                                        Sodium ethanoate + water


                                                              Alkali B


            Sodium ethanoate                                                                                                Ester C
                                              Sodium                                          Ethanol +
                       +                                          Ethanoic acid                                                  +
                                                                                              catalyst D
                    gas A                                                                                                    water


                                              Sodium carbonate



                                      Carboxylic acid salt E + water + carbon dioxide

            Give the name of:

            (i)     gas A,

                    ............................................................................................................................
                                                                                                                                                        (1)

            (ii)    alkali B,

                    ............................................................................................................................
                                                                                                                                                        (1)

            (iii)   ester C,

                    ............................................................................................................................
                                                                                                                                                        (1)

            (iv)    catalyst D,

                    ............................................................................................................................
                                                                                                                                                        (1)

            (v)     carboxylic acid salt E.

                    ............................................................................................................................
                                                                                                                                                        (1)
                                                                                                                                            (Total 9 marks)




Bryngwyn School                                                                                                                                         40
30.   This label has been taken from a bottle of household ammonia solution.



                               Smith’s Household
                               Ammonia Solution
                                                                                         Ideal for all
                                                                                         household
                                                                                         cleaning tasks!

                                                                                         Nothing shifts
                                                                                         grease like
                                                                                         Smith’s does!

      Household ammonia is a dilute solution of ammonia in water. It is commonly used to remove
      grease from ovens and windows.

      (a)   The amount of ammonia in household ammonia can be found by titration.

            25.0 cm3 of household ammonia is placed in a conical flask. Describe how the volume of
            dilute nitric acid required to neutralise this amount of household ammonia can be found
            accurately by titration. Name any other apparatus and materials used.

            To gain full marks you should write down your ideas in good English. Put them into a
            sensible order and use correct scientific words.

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                   (4)




Bryngwyn School                                                                                                                                    41
      (b)   In an experiment, it was found that 25.0 cm3 of household ammonia was neutralised by
            20.0 cm3 of dilute nitric acid with a concentration of 0.25 moles per cubic decimetre.

            The balanced symbol equation which represents this reaction is

                                              NH3(aq) + HNO3(aq)  NH4NO3(aq)

            Calculate the concentration of the ammonia in this household ammonia in moles per cubic
            decimetre.

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

                                               Concentration = ............................. moles per cubic decimetre
                                                                                                                                                           (2)

      (c)   The salt, ammonium nitrate, is formed in this reaction.

            Describe, and give the result of, a chemical test which shows that ammonium nitrate
            contains ammonium ions.

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................

            ....................................................................................................................................
                                                                                                                                                           (2)
                                                                                                                                               (Total 8 marks)




Bryngwyn School                                                                                                                                            42
31.   This label has been taken from a packet of SuperClean.




      Sodium percarbonate is a powerful stain removing chemical.

      The formula of sodium percarbonate can be represented as Na2C2O6

      (a)   (i)    Calculate the number of moles of sodium percarbonate in the 50 g packet.

                   Relative atomic masses: C = 12; O = 16; Na = 23.

                   ...........................................................................................................................

                   ...........................................................................................................................

                                                                          Number of moles = .....................................
                                                                                                                                                 (2)

            (ii)   Calculate the concentration of the sodium percarbonate solution, in moles per cubic
                   decimetre, when 50 g of sodium percarbonate is dissolved in 6 litres (dm3) of water.

                   ...........................................................................................................................

                   ...........................................................................................................................

                                                      Concentration = ....................moles per cubic decimetre
                                                                                                                                                 (1)




Bryngwyn School                                                                                                                                  43
      (b)   When sodium percarbonate acts as a stain removing chemical, it decomposes to produce
            oxygen.

            The equation which represents the decomposition of sodium percarbonate is

                                             2Na2C2O6  2Na2CO3 + 2CO2 + O2

            (i)    Calculate the number of moles of oxygen produced from 50 g of sodium
                   percarbonate.

                   ...........................................................................................................................

                   ...........................................................................................................................

                                                                          Number of moles = .....................................
                                                                                                                                                       (1)

            (ii)   Calculate the volume of oxygen, at room temperature and pressure, produced from
                   50 g of sodium percarbonate.

                   1 mole of any gas at room temperature and pressure has a volume of 24 dm3.

                   ...........................................................................................................................

                   ...........................................................................................................................

                                                                         Volume of oxygen = ............................ dm3
                                                                                                                                                       (2)
                                                                                                                                           (Total 6 marks)



32.   Many soft drinks contain citric acid.




                                                                 Ingredients: carbonated water, sugar,
                                                                 citric acid, acidity regulator (E331),
                                                                 flavourings, preservative (E211)




Bryngwyn School                                                                                                                                        44
      (a)   In 1883, a young chemist called Svante Arrhenius suggested that a molecule can break
            into ions when dissolved in a solvent. He later developed this theory to explain what
            happens when an acid dissolves in water.

            Older scientists believed that molecules could not break up and could not carry an
            electrical charge.

            (i)       Use the ideas of Arrhenius to explain why the Lemon ’n Lime drink is acidic.

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                           (2)

            (ii)      Suggest why older chemists would not accept Arrhenius’ ideas.

                      ...........................................................................................................................

                      ...........................................................................................................................

                      ...........................................................................................................................
                                                                                                                                                           (1)

      (b)   Citric acid is a weak acid.

            Explain, in terms of ions, why Lemon ’n Lime is safe to drink, whereas a solution
            containing a strong acid may be corrosive.

            .....................................................................................................................................

            .....................................................................................................................................

            .....................................................................................................................................
                                                                                                                                                           (2)
                                                                                                                                               (Total 5 marks)




Bryngwyn School                                                                                                                                            45
33.   (a)   This label has been taken from a bottle of vinegar.



                                                        es or preserva
                                                  dditiv              tive
                                               noa                         s

                                  MALT
                                VINEGAR                   Pure
                                                               Malt Vinega
                                                                          r



            Vinegar is used for seasoning foods. It is a solution of ethanoic acid in water.

            In an experiment, it was found that the ethanoic acid present in a 15.00 cm3 sample of
            vinegar was neutralised by 45.00 cm3 of sodium hydroxide solution, of concentration
            0.20 moles per cubic decimetre (moles per litre).

            The equation which represents this reaction is

                                CH3COOH +                   NaOH                 CH3COONa + H2O

            Calculate the concentration of the ethanoic acid in this vinegar:

            (i)    in moles per cubic decimetre (moles per litre)

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                                      Concentration = ................................... moles per cubic decimetre
                                                                                                                                                 (2)

            (ii)   in grams per cubic decimetre (grams per litre).

                   Relative atomic masses: H = 1; C = 12; O = 16.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                                      Concentration = ................................... grams per cubic decimetre
                                                                                                                                                 (2)

Bryngwyn School                                                                                                                                  46
      (b)   Further titrations were carried out to investigate other brands of vinegar. The same method
            was used as in part (a).

            The titration was performed three times for each brand of vinegar.

                                          Volume of 0.20 mol dm–3 sodium hydroxide solution needed to
                                                     neutralise 15 cm3 of the vinegar in cm3
                                             Brand 1                      Brand 2                      Brand 3                      Brand 4
              Titration 1                       45.4                         46.3                         45.8                        46.1
              Titration 2                       44.7                         44.5                         45.4                        45.0
              Titration 3                       45.1                         45.1                         45.6                        45.1

            (i)    Which brand of vinegar appears to contain the highest concentration of ethanoic
                   acid?

                                                                                                                 Brand ...................

                   Explain how you decided.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................
                                                                                                                                                       (2)

            (ii)   Are the results of these titrations good enough to be certain which brand contains
                   the most ethanoic acid?

                   Explain your answer.

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................

                   ...........................................................................................................................
                                                                                                                                                       (2)
                                                                                                                                           (Total 8 marks)




Bryngwyn School                                                                                                                                        47

				
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