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CAIE A Level Chemistry 9701 · Electrochemistry

Electrochemistry: compare question

Compare5 marksStandard

Acidified potassium dichromate(VI) reacts with sodium sulfite. The ionic equation for the reaction is shown.

CrX2OX7X2−(aq)+3 SOX3X2−(aq)+8 HX+(aq)→2 CrX3+(aq)+3 SOX4X2−(aq)+4 HX2O(l)\ce{Cr2O7^{2-}(aq) + 3SO3^{2-}(aq) + 8H+(aq) -> 2Cr^{3+}(aq) + 3SO4^{2-}(aq) + 4H2O(l)}

(a) Using Roman numerals to show oxidation numbers, compare the change in oxidation number of chromium with the change in oxidation number of sulfur in this reaction.

(b) Explain, in terms of electron transfer, what happens to the dichromate ion and to the sulfite ion in this reaction.

(c) State which reactant is the oxidising agent and which is the reducing agent.

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