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This question is about chemical analysis - AQA - GCSE Chemistry - Question 7 - 2015 - Paper 3
Question 7
This question is about chemical analysis. A student has solutions of three compounds, X, Y and Z. The student uses tests to identify the ions in the three compound... show full transcript
Worked Solution & Example Answer:This question is about chemical analysis - AQA - GCSE Chemistry - Question 7 - 2015 - Paper 3
Step 1
Identify the two ions present in compound X
Answer
For compound X, the sodium hydroxide test indicates the presence of iron(II) ions, leading to the formation of a green precipitate. When adding hydrochloric acid and barium chloride, a white precipitate indicates the formation of barium sulfate. Therefore, the two ions present in compound X are Fe²⁺ (iron(II)) and SO₄²⁻ (sulfate).
Step 2
Identify the two ions present in compound Y
Answer
For compound Y, the yellow flame test suggests the presence of sodium ions. The lack of reaction in other tests indicates no significant ions other than sodium in compound Y. Therefore, the two ions present in compound Y are Na⁺ (sodium) and I⁻ (iodide).
Step 3
Identify the two ions present in compound Z
Answer
For compound Z, the tests suggest that there are no significant ions precipitated with sodium hydroxide. However, the cream precipitate formed with nitric acid and silver nitrate indicates the presence of bromide ions. Therefore, the two ions present in compound Z are Fe³⁺ (iron(III)) and Br⁻ (bromide).
Step 4
Compare the advantages and disadvantages of Method 1
Answer
Method 1 involves using sodium sulfate, which can provide accurate weighing results. However, disadvantages include that not all barium sulfate may precipitate, and the sample may take longer to process due to filtration and drying.
Step 5