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David J. Hughes

Why is sodium bicarbonate added in iodometry?

Angi B  Follow

Acidic medium is required for potassium dichromate or permanganate to behave as an oxidizing agent, but in acidic conditions aerial oxidation of iodine also occurs, as a side reaction, to form hypoiodite and iodate ion which are oxidising agents . To manage this condition we add a pinch of sodium bicarbonate in mixture of potassium dichromate , sulphuric acid and potassium iodide.

Further sodium thiosulphate also decomposes to sulphur in acidic condition. Thus a base is required to control the side reactions.

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CaiLei  Follow

Sodium thiosulfate the usual titrant used for iodometric titrations. To keep the thiosulfate solution stable, NaHCO3 , which is a weak base helps to keep the solution slightly alkaline to slow down the decomposition of thiosulfate.

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