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C1a_5_Flame_Colours

VIEWS: 2 PAGES: 4

									                                 GRIFFIN EDUCATION working with
                                EDU-LAB and The RADMASTE Centre

                           UNIT C1a TOPIC 5 PATTERNS IN PROPERTIES


                                    FLAME COLOURS STUDENT WORKSHEET

                                                     REQUIREMENTS

Apparatus:      1 x microburner; 1 x box of matches; 1 x glass rod; 1 x comboplate ; 5 x propettes; towelling paper.
                                                                                   ®




Chemicals:      Methylated spirits; Copper nitrate solution (Cu(NO ) (aq)) [0,5 M];
                                                                     3   2

                Saturated sodium chloride solution (NaCl(aq)); Potassium nitrate solution (KNO (aq)) [1.3 M];
                                                                                               3

                Calcium oxide powder (CaO(s)); Nitric acid (HNO (aq)) [6 M]; Tap water.
                                                                 3




                                                           PROCEDURE

          The flame colours are more easily observed if the experiment is carried out in dim light, such as a room
          with drawn curtains.


1.       Place 2 level spatulas of calcium oxide powder in well F1 of the comboplate .
                                                                                       ®




2.       Use a clean dry propette and add nitric acid drop-by drop to well F1. Keep adding the nitric acid until the
         reaction in the well subsides.
3.       Set up the microburner in one of the empty big wells. Light the burner. (See Question 1)
4.       Dip the glass rod in well F1, and immediately hold the glass rod in the flame of the microburner. Take note of
         the flame colour.
5.       Rinse the glass rod in the tap water and dry it with the towelling paper.
6.       Use a clean, dry propette to add 5 drops of copper nitrate solution to well A1. Use another propette to add 5
         drops of sodium chloride solution to well A3. Add 5 drops of potassium nitrate solution to well A5 with another
         clean propette.


Flame Tests                                                                                              Page 1 of 4
7.       Dip the glass rod into the copper nitrate solution in well A1, and hold the rod in the flame. Take note of the
         colour of the flame.
8.       Rinse the glass rod in the tap water and dry it with the towelling paper.
9.       Repeat steps 7 and 8 with the sodium chloride and potassium nitrate solutions in wells A3 and A5.
         (See Question 3)

                                             Clean all apparatus thoroughly.




                                                        QUESTIONS
Q1.    Draw up a table to summarise your observations in this experiment. Include in it the salt solution you used, the
       metal ions present in the solution and the flame colours.
Q2.    Write a word equation for the reaction that took place in well F1.
Q3.    Write a balanced chemical equation for the reaction that took place in well F1.




Flame Tests                                                                                               Page 2 of 4
                                                  FLAME COLOURS

                                                   TEACHER GUIDE

1. Chemicals
All of the required chemicals are listed in the worksheet. Tap water is also needed.

2. Equipment
Most of the apparatus required can be found in a Basic or Advanced Microchemistry Kit. Paper towelling is needed to
dry the glass rod between testing of the different solutions.

3. Hints
  It is a good idea to perform this experiment in a room with subdued lighting because the flame colours are more
easily observed in dim light. This can be achieved by drawing the curtains (or dropping blinds) in the classroom. If the
room in which the experiment is performed does not have curtains or blinds, overhead lights can be switched off to
darken the room.

  Once the end of the glass rod has been immersed in a solution to be tested, it must immediately be placed in the
flame of the microburner to ensure that the colour of the metal ion is observed.

  It is important to rinse the glass rod with tap water and dry it before testing the next solution. It may happen that a
residue forms at the end of the rod where it has been held in the flame. If this residue is not removed with rinsing and
drying, the other solutions will become contaminated.

  You may wish to extend the experiment by giving unknown solutions for learners to test. They can be asked to
identify which metal ions (Ca2+, Cu2+, Na+ or K+) are in the solution.

4. Cautions
Please remember the following cautions and inform your students of all safety hazards:

Nitric acid is corrosive. If any acid is spilt on the skin, the affected area must immediately be rinsed with copious
amounts of water. Severe burns must receive medical attention.

Never point a propette or a syringe containing acid upwards. A momentary lapse of concentration can result in a
nasty accident. If any acid is squirted

into the eye, immediately rinse the eye out under running water. Always have a dilute solution of sodium
hydrogencarbonate (household baking soda), or milk close by to apply to the injury. These substances will help
neutralise the acid in the eye. The patient should be referred to a doctor.

Never allow the learners to play with matches. Treat any burn with cold running water or ice, and seek medical
assistance where necessary.




Flame Tests                                                                                               Page 3 of 4
5. Model Answers to Questions in the Worksheet


It is recommended that learners write down all of the questions and answers in their workbooks. If this is done, then
the answers to questions do not have to be in full sentences. If the learners do not copy the questions into their
workbooks, then answers should be written in full sentences. Note that some of the questions can only be answered by
learners in higher grades. Word equations can be written instead of chemical equations where required.


Q1.      Draw up a table to summarise your observations in this experiment. Include in it the salt solution you used, the
         metal ions present in the solution and the flame colours.
A1.
                 Salt solution                    Metal ions in solution                    Flame colour

                Ca(NO3)2 (aq)                            Ca2+ (aq)                               red

                Cu(NO3)2 (aq)                            Cu2+ (aq)                              green

                  NaCl (aq)                              Na+ (aq)                               yellow

                  KNO3 (aq)                               K+ (aq)                               purple


Q2.      Write a word equation for the reaction that took place in well F1.
A2.      Calcium oxide(s) + nitric acid(aq)  calcium nitrate(aq) + water(l)


Q3.      Write a balanced chemical equation for the reaction that took place in well F1.
A3.      CaO(s) + 2HNO3(aq)  Ca(NO3)2(aq) + H2O(l)




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