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Substance X is an ammonium salt - Edexcel - GCSE Chemistry - Question 6 - 2013 - Paper 1
Question 6
Substance X is an ammonium salt. (i) Complete the sentence by putting a cross (✗) in the box next to your answer. A test was carried out to find which anion is pre... show full transcript
Worked Solution & Example Answer:Substance X is an ammonium salt - Edexcel - GCSE Chemistry - Question 6 - 2013 - Paper 1
Step 1
(i) Complete the sentence by putting a cross (✗) in the box next to your answer.
Answer
The anion present in substance X is A carbonate ion, CO₃²⁻. This can be inferred from the effervescence observed when diluted hydrochloric acid is added, which indicates the presence of a carbonate ion that releases carbon dioxide gas.
Step 2
(ii) Describe how sodium hydroxide solution can be used to show that ammonium ions are present in substance X.
Answer
To test for ammonium ions, a few drops of sodium hydroxide solution can be added to a sample of substance X and then gently heated. If ammonium ions are present, ammonia gas will be released, which can be detected by its characteristic smell or by using moist red litmus paper that turns blue due to the alkaline nature of ammonia.
Step 3
Step 4
Explain how, using chemical tests, the technician could find out if the substance left in the beaker was potassium sulfate, potassium iodide, sodium sulfate or sodium iodide.
Answer
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Test for Cations: Perform a flame test. If the flame is yellow/not lilac, sodium ions are present; if it is lilac, potassium ions are present.
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Test for Iodide Ions: Dissolve a small sample in water, then add dilute nitric acid followed by silver nitrate solution.
- If a yellow precipitate forms, iodide ions (I⁻) are present:
ightarrow AgI (s)$$
- If no precipitate forms, sulfate ions may be present.
- Test for Sulfate Ions: If no iodide precipitate forms, add dilute hydrochloric acid and then barium chloride solution. A white precipitate indicates sulfate ions are present:
ightarrow BaSO_4 (s)$$