8.2.1 Required Practical 11

Aim:

Carry out simple test-tube reactions to identify transition metal ions in aqueous solution

Method

Apparatus

• Solution Q
• Solution R
• Solution S
• 1.0 mol dm³ sodium hydroxide solution
• 1.0 mol dm³ sodium carbonate solution
• 0.05 mol dm³ silver nitrate solution
• 12 test tubes
• Test-tube rack
• 7 dropping pipettes
• 250 cm³ beaker
• Hot water
• Distilled / deionised water

Test 1a:

• Add 10 drops of the solution into a test tube.
• Gradually add sodium hydroxide solution, shaking the test tube gently.
• Continue adding dropwise until the sodium hydroxide is in excess.
• Record your observations.
• Do not discard the mixture after the test.

Test 1b:

• Half fill a 250 cm³ beaker with freshly boiled water.
• Place the test tubes from Test 1a into the beaker of hot water and allow them to stand for approximately 10 minutes.
• Observe and record any changes.

Test 2:

• Add 10 drops of sodium carbonate solution to a test tube.
• Add 10 drops of the test solution and shake the mixture gently.
• Record all observations.

Test 3:

• Add 10 drops of the test solution into a test tube.
• Add 10 drops of silver nitrate solution, then gently shake the mixture.
• Allow the test tubes to stand for approximately 10 minutes, and record any observations.

Results

Evaluation

• The results from all three tests are used to identify the ions present in solutions Q, R and S

Practical Tip:

• Always ensure test tubes and pipettes are thoroughly clean, as the tests are highly sensitive, and cross-contamination could affect the results.
• Label your test tubes clearly to prevent confusion, particularly if multiple tubes contain similar-looking solutions, especially when placed in a water bath without a test tube rack.
• For clearer observation of any colour changes, it is helpful to place the test tubes against a white background, such as a sheet of paper.