Required Practical 11

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

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

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

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
Stand in water bath	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	light brown precipitate

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
- Light brown precipitate suggests a Fe³⁺ cation
- This would be formed by the oxidation of the Fe²⁺ cation
Anion = cannot be determined
Cation = iron(II) / Fe²⁺

Required Practical 11 (AQA A Level Chemistry)

Revision Note