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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 pres... show full transcript
Worked Solution & Example Answer:Substance X is an ammonium salt - Edexcel - GCSE Chemistry - Question 6 - 2013 - Paper 1
Step 1
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 is indicated by the effervescence when hydrochloric acid is added, which suggests that carbon dioxide is being released, confirming the presence of carbonate ions.
Step 2
Describe how sodium hydroxide solution can be used to show that ammonium ions are present in substance X.
Answer
To test for ammonium ions, sodium hydroxide solution is added to the sample.
Upon heating, if ammonium ions are present, ammonia gas is released. This can be detected by its characteristic pungent odor or by using moist red litmus paper, which will turn blue due to the basic 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 the cation: Perform a flame test on the crystals. If the flame is yellow, sodium ions are present; if it's lilac, potassium ions are present.
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Test for iodide ions: Dissolve a small sample in water and add dilute nitric acid followed by silver nitrate solution. If a yellow precipitate forms, iodide ions are present (indicating potassium iodide). If no precipitate forms, then proceed to the next test.
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Test for sulfate ions: To the solution, add dilute hydrochloric acid followed by barium chloride solution. If a white precipitate forms, sulfate ions are present (indicating potassium or sodium sulfate). If there's no precipitate, then the compound is confirmed as sodium iodide or potassium iodide, depending on previous tests.