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 in compound X
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Answer
Compound X shows no colour in the flame test and produces a white precipitate when sodium hydroxide is added. This suggests the presence of Fe²⁺ ions, indicating that compound X is iron(II) sulfate (FeSO₄).
Step 2
Identify the two ions in compound Y
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Answer
The yellow flame indicates the presence of sodium ions (Na⁺). There are no notable reactions with sodium hydroxide or acid solutions, confirming the presence of Na⁺ ions in compound Y.
Step 3
Identify the two ions in compound Z
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Answer
The absence of a flame colour and the formation of a brown precipitate indicate the presence of Fe³⁺ ions, implying that compound Z is iron(III) bromide (FeBr₃).
Step 4
Compare the advantages and disadvantages of Method 1
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Answer
Method 1 includes accurate weighing of barium sulfate, which allows for reliable concentration calculations. However, there are drawbacks such as the possibility that not all barium sulfate may precipitate, potential loss of precipitate, and the process requires more time and energy to filter and dry the precipitate.
Step 5
Compare the advantages and disadvantages of Method 2
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Method 2 is more straightforward and works well for lower concentrations due to the precision of titration. It avoids issues related to filtration and drying, making it faster. However, it requires careful measurement of the hydrochloric acid and assumes complete reaction with the barium hydroxide.
