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The following procedure is proposed to test for the presence of lead(II) and barium ions in water at concentrations of 0.1 mol L⁻¹ - HSC - SSCE Chemistry - Question 27 - 2024 - Paper 1
Question 27
The following procedure is proposed to test for the presence of lead(II) and barium ions in water at concentrations of 0.1 mol L⁻¹. 1. Add excess 0.1 mol L⁻¹ sodium... show full transcript
Worked Solution & Example Answer:The following procedure is proposed to test for the presence of lead(II) and barium ions in water at concentrations of 0.1 mol L⁻¹ - HSC - SSCE Chemistry - Question 27 - 2024 - Paper 1
Step 1
Add excess 0.1 mol L⁻¹ sodium sulfate solution.
Answer
When barium ions (Ba²⁺) are present in the solution, adding sodium sulfate will result in a reaction that forms barium sulfate, which is insoluble and precipitates out. The equation for this reaction is:
ightarrow BaSO_4(s)$$ Therefore, if a precipitate is observed, it indicates the presence of barium ions.Step 2
Step 3
Add excess 0.1 mol L⁻¹ sodium bromide solution to the filtrate.
Answer
If lead(II) ions (Pb²⁺) are present in the filtrate, they will react with the sodium bromide to form lead(II) bromide, another insoluble compound that will precipitate. The relevant chemical equation is:
ightarrow PbBr_2(s)$$ However, if both barium and lead(II) ions are initially present, the formation of barium sulfate in step 1 would precipitate barium before any assessment of lead(II) can occur. Thus, the process fails to detect lead(II) ions if barium is already precipitated.