Identifying Transition Metal Ions (Oxford AQA International A Level Chemistry)
Revision Note
Written by: Richard Boole
Reviewed by: Stewart Hird
Required Practical 9: Transition Metal Ions in Aqueous Solution
Objective
To carry out simple test–tube reactions to identify transition metal ions in aqueous solution.
Apparatus
Solution Q
Solution R
Solution S
1.0 mol dm-3 sodium hydroxide solution
1.0 mol dm-3 sodium carbonate solution
0.05 mol dm-3 silver nitrate solution
12 test tubes
Test-tube rack
7 dropping pipettes
250 cm3 beaker
Hot water
Distilled / deionised water
Method
Test 1 - part a
Note the initial colour of solution Q
Place 10 drops of solution Q in a test tube
Add sodium hydroxide solution, dropwise with gentle shaking, until in excess
Keep the test tube for part b
Record any observations in an appropriate table
Repeat this test with solutions R and S
Test 1 - part b
Half fill a 250 cm3 beaker with freshly boiled water
Stand the three test tubes from part a in the beaker of hot water for about 10 minutes
Record any observations in an appropriate table
Test 2
Place 10 drops of sodium carbonate solution in a test tube
Add 10 drops of solution Q
Shake the mixture gently
Record any observations in an appropriate table
Repeat this procedure with solutions R and S
Test 3
Place about 10 drops of solution Q in a test tube
Add about 10 drops of silver nitrate solution and shake the mixture gently
Repeat this procedure with solutions R and S
Allow the three test tubes to stand for about 10 minutes
Record any observations in an appropriate table
Practical Tip
Always use clean test tubes and pipettes as the tests are very sensitive and you don't want to cross-contaminate the solutions
It's a good idea to label your test tubes to avoid confusing ones that have the same appearance, especially when they are in a water bath and not arranged in a test tube rack
To observe colour changes more clearly, using a white background such as a piece of paper can help
Results
The results for this required practical are the observations of solutions Q, R and S in tests 1, 2 and 3
A suitable results table could be:
Test | Q | R | S |
|---|---|---|---|
1a - Initial colour | |||
1a - Add NaOH (aq) | |||
1a - Stand in water bath | |||
2 - Add Na2CO3 (aq) | |||
3 - Add AgNO3 (aq) |
Evaluation
The results from all three tests are used to identify the ions present in solutions Q, R and S
Worked Example
The following tests were completed on solutions Q, R and S. The results are shown in the table.
Test | Q | R | S |
|---|---|---|---|
Initial colour | yellow solution | light blue solution | pale green solution |
Add NaOH (aq) | orange/brown precipitate | blue precipitate | grey/green precipitate |
Add excess NaOH (aq) | no visible change | no visible change | no visible change |
Add Na2CO3 (aq) | orange/brown precipitate and effervescence | blue green precipitate | grey/green precipitate |
Add AgNO3 (aq) | no visible change | white precipitate | no visible change |
Identify the anions and cations present, where possible, in solutions Q, R and S.
Answers:
Solution Q - 0.2 mol dm-3 iron(III) nitrate solution
Solution R - 0.2 mol dm-3 copper(II) chloride solution
Solution S - 0.5 mol dm-3 ammonium iron(II) sulfate solution
Solution Q
Test 1 results
Yellow solution suggests a Fe3+ cation
Orange brown precipitate with NaOH (aq) suggests a Fe3+ cation
No further change with excess NaOH (aq) suggests a Fe3+ cation
Test 2 results
Orange/brown precipitate and effervescence suggests a Fe3+ cation
Test 3 results
No visible change suggests the anion is not a halide ion
Anion = cannot be determined
Cation = iron(III) / Fe3+
Solution R
Test 1 results
Light blue solution suggests a Cu2+ cation
Blue precipitate with NaOH (aq) = suggests a Cu2+ cation
No further change with excess NaOH (aq) suggests a Cu2+ cation
Test 2 results
Blue/green precipitate and effervescence suggests a Cu2+ cation
Test 3 results
White precipitate suggests a Cl- anion
Anion = chloride / Cl-
Cation = copper(II) / Cu2+
Solution S
Test 1 results
Pale green solution suggests a Fe2+ cation
Grey / green precipitate with NaOH (aq) suggests a Fe2+ cation
No further change with excess NaOH (aq) suggests a Fe2+ cation
Test 2 results
Grey/green precipitate suggests a Fe2+ cation
Test 3 results
No visible change suggests the anion is not a halide ion
Anion = cannot be determined
Cation = iron(II) / Fe2+
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