Is it possible to: a) oxidize iodide ions to free iodine by the action of bertolet salt in an acidic medium; b) Cl ions into free chlorine; c) by the action of potassium dichromate in an acidic medium, oxidize the arsenite ion into the arsenate ion? Why, when oxalic acid (or oxalate) is titrated, do the first drops of a permanganate solution discolour slowly, while in the future this discolouration occurs almost instantly? What can be done so that the first drops of KMnO4 also instantly discolor?

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