During a qualitative test to identify halide ions, a student adds concentrated sulfuric acid to a solid sample of potassium iodide. They observe the evolution of a gas with a rotten egg smell (H2S\text{H}_2\text{S}H2S) alongside purple vapours of iodine.
Which statement correctly explains the redox process involving sulfur during this reaction?
Sulfur in H2SO4\text{H}_2\text{SO}_4H2SO4 (oxidation state +4+4+4) is reduced to an oxidation state of −2-2−2 in H2S\text{H}_2\text{S}H2S by gaining 666 electrons.
Sulfur in H2SO4\text{H}_2\text{SO}_4H2SO4 (oxidation state +6+6+6) is oxidised to an oxidation state of −2-2−2 in H2S\text{H}_2\text{S}H2S by losing 888 electrons.
Sulfur in H2SO4\text{H}_2\text{SO}_4H2SO4 (oxidation state +6+6+6) is reduced to an oxidation state of −2-2−2 in H2S\text{H}_2\text{S}H2S by gaining 888 electrons.
Sulfur in H2SO4\text{H}_2\text{SO}_4H2SO4 (oxidation state +6+6+6) is reduced to an oxidation state of 000 in H2S\text{H}_2\text{S}H2S by gaining 666 electrons.
Practise Edexcel GCSE Chemistry Qualitative analysis: tests for ions with exam-style questions for Foundation and Higher tier. 127 questions, matched to the Edexcel GCSE Chemistry (1CH0) specification and written in Paper 1 and Paper 2 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.
