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Potash alum is a chemical compound - AQA - GCSE Chemistry - Question 7 - 2021 - Paper 2
Question 7
Potash alum is a chemical compound. The formula of potash alum is KAl(SO₄)₂ 07.1 Give a test to identify the Group 1 metal ion in potash alum. You should include th... show full transcript
Worked Solution & Example Answer:Potash alum is a chemical compound - AQA - GCSE Chemistry - Question 7 - 2021 - Paper 2
Step 1
Give a test to identify the Group 1 metal ion in potash alum.
Answer
To identify the Group 1 metal ion in potash alum, perform a flame test. First, take a small sample of the potash alum and moisten it with distilled water. Hold the sample in a clean platinum wire and place it in a Bunsen burner flame.
The result of the test should show a lilac flame, indicating the presence of potassium ions (K⁺).
Step 2
Name one instrumental method that could identify the Group 1 metal ion and show the concentration of the ion in a solution of potash alum.
Answer
One instrumental method that could identify the Group 1 metal ion and show its concentration in a solution of potash alum is flame emission spectroscopy.
Step 3
Step 4
What additional step is needed so that the other metal ion in potash alum can be identified?
Answer
To identify the other metal ion in potash alum, add excess sodium hydroxide solution to the test solution. This will help to confirm the presence of aluminum ions.
The result of this additional step would be that the white precipitate forms initially but may dissolve upon the addition of excess sodium hydroxide, indicating a complex formation.
Step 5
Describe a test to identify the presence of sulfate ions in a solution of potash alum.
Answer
To identify the presence of sulfate ions (SO₄²⁻) in a solution of potash alum, add barium chloride (solution) to the solution. This reaction forms a white precipitate of barium sulfate (BaSO₄) if sulfate ions are present.
The result of the test would be the formation of the white precipitate, confirming the presence of sulfate ions.