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Lab 12 - What is a Chemical Reaction

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					                                           LAB # 12
                 Lab: What Is a Chemical Reaction?
Objectives
      examine the chemical properties of hydrochloric acid and copper chloride
      identify the types of reactions they undergo
      identify signs of a chemical reaction
      determine if the law of conservation of mass applies to a sample chemical reaction in one of these series


Introduction
A chemical change is defined as a change in the composition and properties of a substance. The
transformation of old materials (reactants) into new substances (products) as a result of a chemical change is
called a chemical reaction. Both in the natural world and in the laboratory we recognize that a chemical
reaction has occurred by observing the appearance of products with physical and chemical properties different
from the reactants from which they were made.

There are many types of observable changes that are used to identify that a chemical reaction has occurred.
Signs of chemical change include:

      formation of a precipitate (solid formed upon mixing of two solutions)
      release of gas bubbles that are not due to a physical change (such as boiling or sublimation)
      a color change that does not result from dilution or color mixing
      a temperature change (exothermic or endothermic) that is not caused by external heating or cooling

These signs of change illustrate the dynamic nature of chemical reactions. What they do not reveal, however, is
where the real action is taking place-at the level of atoms and molecules. Chemical reactions arise due to the
rearrangement of atoms and molecules. In rearrangement reactions molecules of one compound can exchange
atoms or groups of atoms with other elements or compounds, generating new substances.. Rearrangement
reactions are of two types: 1) single replacement where one element replaces another element in a compound,
and 2) double replacement reactions where two compounds exchange atoms or groups of atoms. Chemical
reactions also arise when compounds are formed when atoms combine to form molecules , when two molecules
combine to form a bigger molecule, or when an atom and a molecule combine to form a new molecule.
Conversely, in a third type of chemical reaction, the forces or bonds linking atoms together within a compound
break causing it to decompose and reform its constituent elements, two or more new compounds, or a
combination of atom(s) and new compound(s)

We cannot see these rearrangements at the atomic level. What evidence do we have for them? The law of
conservation of mass states that in any physical or chemical reaction, mass is neither created nor destroyed-
it is conserved. This implies that atoms are not gained or lost in a chemical reaction, they are only rearranged.


                                                                                                                1
Materials
   aluminum , foil, 1-cm piece
   aluminum, granular                                                   beaker, 150-mL (for rinse water)
   aluminum, shot, 2 small pieces                                       chemical scoop
   ammonium hydroxide solution, NH4OH, 3M, 1-mL                         distilled water and wash bottle
   copper (II) chloride solution, CuCl2, 0.5M, 16-mL                    electronic gram balance
   hydrochloric acid solution, HCl, 2M, 6-mL                            Erlenmeyer flask, 125-mL
   magnesium ribbon, 1-cm piece                                         forceps
   silver nitrate solution, AgNO3, 0.1M, 5-mL                           graduated cylinder, 10-mL
   sodium carbonate solution, Na2CO3, 0.5M, 1-mL                        litmus paper, *blue
   sodium bicarbonate, NaHCO3, 0.1 g                                    paper towels
   sodium hydroxide solution, NaOH, 2M, 1-mL                            pipet, Beral-type, graduated, 5
   zinc, granular                                                       reaction plate, 24-well
   zinc, mossy, small pieces                                            rubber stopper (to fit Erlenmeyer flask)
                                                                         culture tube13 x 100 mm
                                                                         thermometer
                                                                         white paper


    *Blue litmus paper is blue in basic or neutral solutions and turns PINK in acidic solutions
                  Don’t touch the litmus paper with wet hands!!!!!!!!!!!!!!!!

Safety Precautions
Hydrochloric acid and sodium hydroxide are corrosive to skin and eyes. Ammonium hydroxide is also
irritating to eyes and lungs. Copper (II) chloride is highly toxic by ingestion and silver nitrate will stain skin
and clothes. Magnesium is a flammable solid and zinc metal dust may also be flammable; do not use near
flames. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant
gloves, and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the lab.




Answer the pre-lab questions found at the end of this lab
packet. Tear off the answer sheet and turn it in by:
_________




                                                                                                                     2
Procedures
     General Guidelines
            1. Place the 24-well reaction plate
               on a piece of white paper as
               shown.
            2. Pour distilled water into a 150-
               mL beaker until it is about ½full
               . Use this as rinse water for the
               thermometer after each use.
            3. Use a thermometer to measure
               the temperature of each solution
               after each reaction. Briefly rinse
               the thermometer in the distilled water and pat it dry between steps.
            4. Record all immediate changes in each reaction step. If evidence of reaction continues
               beyond 1-2 minutes, proceed with the next step in the sequence. Record the final appearance
               of each mixture before rinsing and washing the reaction plate.
            5. When adding a solid to a reaction well, always add a small amount (about the size of a pea)
               from the end of a chemical scoop or with a forceps (in the case of metal pieces).

Part A. Reactions of Hydrochloric Acid
     Record all observations in Data Table A.

     For EACH OBSERVATION in PART A record the following 4 things:
       test each solution with the blue litmus paper before and after reaction, record color change
       check temperature of each solution before and after reaction, record any temperature change
       record the disappearance of solids, or the creation of new solids
       record the appearance of bubbles, rate of bubbling, and time until bubbling stops

            6. Using a Beral-type pipet, add 1 mL (≈ 20 drops) of HCl to each well, A1-A6. Record the
               color and appearance of the HCl solution BEFORE reacting.
            7. Measure and record the initial temperature of the solution in well A1. Note: Assume that all
               the other solutions in wells A2-A6 are at the same initial temperature as that of well A1.
            8. Test the solution in well A1 using a piece of blue litmus paper. Note the initial color, then
               add 1 mL of NaOH solution using a Beral-type pipet. Immediately place the thermometer
               back in the well and record any temperature change. After one minute, test the solution again
               with a fresh piece of blue litmus paper.
            9. To well A2, add a small amount of solid NaHCO3. Observe and record all changes,
               including the temperature. Once any initial evidence for reaction has subsided, continue
               adding sodium bicarbonate in small amounts until a total of three portions have been added.
            10. Use a Beral-type pipet to add 1 mL (≈ 20 drops) of AgNO3 solution to well A3. Record
                all observations.


                                                                                                              3
Lab #12 Procedures Continued:
            11. Using a chemical scoop, add a SMALL amount of granular zinc to well A4. Record
                all observations.
            12. Using a chemical scoop, add a SMALL amount of granular aluminum to well A5. Record
                all observations.
            13. To well A6, add one SMALL piece of magnesium ribbon. Record all observations.
            14. Proceed to Part B after noting any changes in the final appearance of the mixtures in wells
                A1-A6.

Clean Up for Part A
     Place several folds of paper towel in the sink and turn the 24-well reaction plate over onto the paper
     towel. Carefully remove the paper towel with the metals from the sink and dispose of it in the
      wastebasket. Rinse the 24-well reaction plate with tap water.


Part B. Reactions of Copper (II) Chloride
     Record all observations in Data Table B
.
     For EACH OBSERVATION in PART B record the following 5 things:
          formation of a precipitate and color of precipitate
          check temperature of each solution before and after reaction, record any temperature change
          color change of solution or metal
          rate of reaction (fast/ slow)
          formation of bubbles

            15. Using a Beral-type pipet, add 1 mL (≈ 20 drops) of CuCl2 to each well, B1-B6. Record the
                and appearance of the solution and measure its initial temperature in one of the wells.
            16. Use forceps to add one SMALL piece of aluminum shot to well B1. Record all
                observations, including the temperature.
            17. Add a SMALL piece of crumpled aluminum foil to well B2. Record all observations.
            18. Use forceps to add one SMALL piece of mossy zinc to well B3. Record all observations.
            19. Use a Beral-type pipet to add 1 mL (≈ 20 drops) of NH4OH solution to well B4. Record all
                observations.
            20. Use a Beral-type pipet to add 1mL (≈ 20 drops) of Na2CO3 solution to well B5. Record all
                observations
            21. Use a Beral-type pipet to add 1mL (≈ 20 drops) of AgNO3 solution to well B6. Record all
                observations
            22. Note any changes in the final appearance of the mixtures in wells B1-B6.



                                                                                                              4
Lab #12 Procedures Continued:

Clean Up for Part B
     Place several folds of paper towel in the sink and turn the 24-well reaction plate over onto the paper
     towel. Carefully remove the paper towel with the metals from the sink and dispose of it in the
      wastebasket. Rinse the 24-well reaction plate with tap water.


Part C. Conservation of Mass
     Be VERY accurate with the recording of the masses in this exercise!

            23. Use a graduated cylinder to add 10 mL of CuCl2 to a 125-mL Erlenmeyer flask.
            24. Rinse the graduated cylinder with distilled water and then use it to add 3 mL of AgNO3
                solution to a 13 x 100 mm culture tube (looks like a mini test tube!)
            25. Carefully place the test tube containing the AgNO3 into the Erlenmeyer flask containing the
                CuCl2. BE CAREFUL not to spill the contents of the test tube in the process. The test tube
                should be standing upright (at a slight angle) in the flask.
            26. Cap the Erlenmeyer flask with a rubber stopper and measure the mass of the entire assembly
                (flask + test tube + contents + rubber stopper). Do not allow the contents of the test tube
                and flask to mix prior to measuring the initial mass. Record this mass in Data Table C.

            27. Hold the flask in one hand so that the stopper will NOT fall out. Gently invert the flask
                several times to allow the two solution to mix.

            28. After the two solutions have mixed, measure the mass of the entire assembly again. Do
                NOT take apart the system prior to measuring the final mass. Record this mass in
                Data Table C.

Clean Up for Part C
     Pour the contents of the Erlenmeyer flask (and any liquid that might still be in the test tube) into the
     waste container indicated by the teacher. Rinse both the Erlenmeyer flask and the test tube with tap
     water.




                                                                                                                5
Data Table A: Reactions of Hydrochloric Acid
For Each Record:
    1. precipitate/ no precipitate                         3.   bubbles/ no bubbles and rate of bubbling
    2. endothermic/ exothermic/ unchanged                  4.   color or no color change of solution

Initial appearance of HCl Solution: ___________________________________________________________
Reaction Well    Reagents                   Observations



     A1          HCl + NaOH




     A2          HCl + NaHCO3




     A3          HCl + AgNO3




     A4          HCl + Zn
                 (use a SMALL
                 amount of granular
                 zinc!)


                 HCl + Al
     A5          (use a SMALL
                 amount of granular
                 aluminum!)




     A6          HCl + Mg
                 (use a SMALL piece
                 of magnesium!)

                                                                                                           6
Data Table B: Reactions of Copper (II) Chloride
For Each Record:
    1. precipitate/ no precipitate and color          4.   color or no color change of solution or metal
    2. endothermic/ exothermic/ unchanged             5.   rate of reaction (fast/ slow)
    3. bubbles/ no bubbles and rate of bubbling

Initial appearance of CuCl2 Solution: _________________________________________________________
Reaction Well    Reagents                 Observations



       B1            CuCl2 + Al(shot)




       B2            CuCl2 + Al(foil)




       B3            CuCl2 + Zn (mossy)




       B4            CuCl2 + NH4OH




       B5            CuCl2 + Na2CO3




       B6            CuCl2 + AgNO3




                                                                                                           7
Data Table C: Conservation of Mass

    Initial mass of flask assembly (g)
    (before mixing)


    Final mass of flask assembly(g)
    (after mixing)


    Δ mass = final mass − initial mass




                                         8
Name _____________________________________________ Date ____________________ Period ______

                     POST-LAB QUESTIONS for LAB 12:
                        What Is a Chemical Reaction?

1.    (a) PRECIPITATES
            i) Which substance(s) formed a precipitate when mixed with HCl?




            ii) Which substance(s) formed a precipitate when mixed with CuCl2?




      (b) BLUE LITMUS PAPER
         i) What color was the blue litmus paper:


            A. in unreacted HCl? _______________


               i) HCl is a(n)   ACID / BASE or NEUTRAL
                                         (circle one)



            B. after reacting HCl with NaOH? _____________________________________________


               ii) after reacting HCl and NaOH the solution is    ACIDIC / BASIC or NEUTRAL
                                                                              (circle one)



            C. after reacting HCl with NaHCO3? ___________________________________________


               iii) after reacting HCl and NaOH the solution is   ACID / BASE or NEUTRAL
                                                                              (circle one)




                                                                                             9
Lab #12 Post-Lab Questions Continued:

          (c) TEMPERATURE CHANGE
                 i) Which substance(s) caused an exothermic reaction with:

                         A.   HCl



                         B. CuCl2




                 ii) Which substance(s) caused an endothermic reaction with HCl?

                         A. HCl



                         B. CuCl2




2.        (a) Fill in the following table describing the reactions of each metal with HCl and CuCl2
                Reaction with HCl                                                Reaction with CuCl2
Metal        Bubbles?           Rate                             Metal        Color             Rate
               Y/ N       Fast / Medium/                                     Change     Fast / Medium/ Slow?
                               Slow?                                          Y/ N
     Al                                                             Al
                                                                 (shot)
     Zn                                                             Al
                                                                  (foil)
     Mg                                                            Zn


3. Based on your observations recorded in 2(a) and (b), predict whether CuCl2 will react with Mg. Explain.




                                                                                                             10
Lab #12 Post-Lab Questions Continued:

     5. a) Was a precipitate created when AgNO3 was added to:


               i) HCl          YES / NO            if yes, what color? ___________________
                                 (circle one)



               ii) CuCl2       YES / NO            if yes, what color? ___________________
                                 (circle one)


        b) What monatomic anion is common to both HCl and CuCl2? ____________



        c) When AgNO3 is added, what monatomic cation is common to each solution? _____________



        d) What is the likely chemical formula for the product common to each reaction? _________________



5.      a) Compare the rate of reactions of CuCl2 with Al (shot) and Al (foil).




        b) Propose a possible reason for any differences in the reaction rate of the two forms of aluminum.




6.      a) Comment on the difference or similarity of the beginning and ending masses for Part C.




                                                                                                              11
Lab #12 Post-Lab Questions Continued:

6. Continued:

      b) Was a precipitate created by the reaction in Part C? YES / NO
                                                               (circle one)


         If yes, what is the probably chemical formula for this precipitate? ____________________


      c) Try writing the balanced chemical equation, including phases of matter, for the reaction Part C.




      d) Does the law of conservation of mass apply to this chemical reaction in Part C?   YES / NO
                                                                                             (circle one)

       e) Justify your answer for 6(d).




                                                                                                            12
Name __________________________________ Date ____________________ Period ______

                          PRE-LAB QUESTIONS for LAB 12:
                            What Is a Chemical Reaction?
   1.   Describe the danger in using each of the following chemical according to this lab.

               a) HCl



               b) NH4OH



               c) CuCl2



   2. Look up the term 'corrosive' and write a chemical based definition.




   3. a) Define a chemical change




        b) Put a check in from of each of the following everyday processes which represent a chemical change:

               _______ i) a nail rusts

               _______ ii) ice melts

               _______ iii) wood burns

               _______ iv) a banana ripens

               _______ v) sugar dissolves in water

   4. Define a chemical reaction in terms of reactants and products.




                                                                                                           13
Lab #12 Pre-Lab Question Continued:
5. a) State the law of conservation of mass.




   b) does the following chemical equation follow the law of conservation of mass? YES       / NO.
                                                                                      (circle one)
                                  H2(g) + O2(g) → H2O(l)
   c) Justify your choice for 5(b)




6. The third paragraph of the Introduction section talks about three (3) different types of chemical
   reactions:
           1) Composition (A.K.A. Synthesis) reactions,
           2) Decomposition reactions,
           3) Rearrangement reactions
                  i) Single Replacement reactions
                  ii) Double Replacement reactions (A.K.A. metathesis) reactions
   Reread the fourth paragraph of the introduction and see if you can correctly identify each of the
   following chemical equations represnet Synthesis (S), Decomposition (D), Single replacement (SR), or
   Double Replacement (DR) chemical reactions.

   _______ a) HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

   _______ b) 2HCl(aq) → H2(g) + Cl2(g)

   _______ c) CuCl2(aq) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2AgCl(s)

   _______ d) HCl(aq) + NaHCO3(aq) → H2CO3(aq) + NaCl(aq)

   _______ e) CuCl2(aq) + Zn(s) → ZnCl2(aq) + Cu(s)

   _______ f) Fe(s) + S(s) → FeS(s)

   _______ g) H2(g) + Cl2(g) → 2HCl(aq)

   _______ h) CuCl2(s) → Cu(s) + Cl2(g)
7. a) Define a precipitate.



   b) Find and circle the only precipitate in the equations of question # 6.
                                                                                                      14
Lab #12 Pre-Lab Question Continued:
8. List the four (4) observations to be made for each reaction in Part A.

           1.


           2.


           3.


           4.



9. List the five (5) observations to be made for each reaction in Part B.


           1.



           2.



           3.



           4.



           5.



10.        a) Try writing the balanced chemical equation, including phases of matter, for the reaction of
              Part C of the Procedures section.




           b) underline the reactants
           c) draw a box around the products
                                                                                                            15
Lab #12 Pre-Lab Question Continued:

11. What color is blue litmus paper in:

           a) acidic solutions? ________________________

           b) basic solutions? _________________________

           c) neutral solutions? _______________________



12. Which of the following represent a physical separation (PS) and which represent a chemical
    separation (CS)?


           _______ a) water is distilled to remove impurities


           _______ b) when an electric current is passed through it, water decomposes into hydrogen gas
                      and oxygen gas

           _______ c) a salt water solution is evaporated to recover the salt


           _______ d) sodium chloride is added to a solution of silver nitrate to remove the silver
                      atoms in the form of a silver chloride precipitate

           _______ e) a solution is filtered to remove the precipitate


           _______ f) when granulated zinc is added to a solution of copper (II) chloride, copper
                      precipitates out of solution and settles at the bottom of the test tube

           _______ g) a test tube containing a solution with solid copper at the bottom is carefully
                      decanted to remove the liquid but retain the solid copper

           _______ h) bubbles of pure hydrogen are recovered from an HCl solution by adding solid
                      aluminum to the solution




                                                                                                       16

				
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