A-LevelChemistryAtoms, molecules and stoichiometryFeb/Mar 2025Paper 3 Q216 Marks
2 Many oxidising agents are able to oxidise acidified potassium iodide to iodine in acidic conditions. The amount of iodine produced can be determined by titrating it with aqueous sodium thiosulfate. I2(aq) + 2Na2S2O3(aq) → 2NaI(aq) + Na2S4O6(aq) You will determine the change in oxidation state of an oxidising agent when it reacts with iodide ions. FA 2 is aqueous sodium thiosulfate, containing 22.00 g Na2S2O3•5H2O (Mr = 248.2) in 1.00dm³. FA 3 is a 0.0175moldm⁻³ solution of an oxidising agent. FA 4 is 0.50 moldm⁻³ potassium iodide, KI. FA 5 is 1.00 moldm⁻³ sulfuric acid, H2SO4. FA 6 is starch solution.
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