| Chemistry Section B : Atoms and Ions
Part 4: Practical Work
A. Experiments to show the presence of certain ions
1. Flame Tests
Many compounds that contain ions give characteristic colours when heated in a flame.
Go to Internet site link
From the homepage go to Activities then Forensic science and then Flame tests. Download the sheet on flame tests including the method and results sheet.
There is also a teachers and technicians sheet.
2. Colour of Aqueous Solutions
Apart from compounds containing ions giving characteristic flame colours, aqueous solutions of these compounds also give characteristic colours.
Look at solutions of the following ionic compounds, record the colour and write down the ion responsible for the colour.
3. Tests for
A. Cations
To test for cations we can use sodium hydroxide and ammonium hydroxide solution. The cations are characterised by the coloured precipitates that are formed as a result of the reactions with the above chemicals.
Method:
*Safety glasses must be worn
*Care with all chemicals as several are corrosive report all spillages to your teacher
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Into a test tube put 1cm3 of the solution containing the cation.
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Now carefully add, dropwise sodium hydroxide solution until no further reaction occurs.
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Record all your observations in the table below.
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Repeat steps 1-3 with all the solutions containing cations.
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Repeat the whole experiment this time using ammonium hydroxide.
B. Anions
To test for anions we use a variety of different reagents depending on the anion you are testing for:
Type of Anion |
Method |
| Halide ions |
Into a test tube put 5 cm3 of the halide ion you are testing.
Add 2-3 drops of silver nitrate solution (AgNO3)
Record the colour of the precipitate formed |
| Sulphate ion |
To 5cm3 of an aqueous solution of the sulphate ion add 2-3 drops of Barium chloride solution.(BaCl2) and record the colour of the precipitate formed |
| Carbonate ion |
To 5cm3 of an aqueous solution of the carbonate ion add drops of dilute hydrochloric acid and record all observations |
* A precipitate is an insoluble substance that is formed when two aqueous solutions are mixed together*
4. Conduction of Ionic Solutions
NB. Ionic compounds consist of ions, covalent compounds do not contain ions
Go to Internet site link
From the homepage go to GCSE worksheets and Activities
Go to module 8 (click on red cross)
Click on N-m08-12 and then print out the sheet 'properties of ionic and covalent compounds'.
Complete the experiment and answer the questions.
5. Migration of Ions
Set up the apparatus as shown below:
Watch what happens, then answer the following questions:
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In which direction does the blue colour of the positive Cu2+ ion move?
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In which direction does the purple colour of the negative MnO42- ion move?
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Mark these observations on the diagram using a blue and purple pencil
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What does this experiment tell you about ions in aqueous solution when an electric current is passed through it?
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Explain carefully how an ionic solution conducts electricity?
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In which direction do the electrons move?
B Electricity from chemicals
Set up the apparatus as shown below:
| 1. |
Observe the voltmeter. Explain what happens and why. |
| 2. |
Repeat the experiment using iron and iron (II) sulphate solution instead of copper and copper (II) sulphate. Explain what happens and why? |
| 3. |
For each of the two experiments: |
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a. Which metal in each case is more able to form ions? |
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b. Which metal will become the negative electrode of the cell and which the positive? |
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c. Draw a simple diagram of the zinc-iron cell showing the direction of the movement of electrons. |
Repeat the experiment with other pairs of metals, state each time which one is to be the negative electrode.
Extra: Investigate how you can make simple cells using a lemon and potatoes and two different metals.
C Electrolysis Experiments
1. Electrolysis of Copper II Sulphate Solution .pdf (D.Hoult)
2. Electrolysis of dilute Sulphuric Acid .pdf (D.Hoult)
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