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Hypochlorite (ClO- ) is the main component of chlorine bleach and is used in the

ID: 1000282 • Letter: H

Question

Hypochlorite (ClO- ) is the main component of chlorine bleach and is used in the paper industry for bleaching paper fibre. Excess hypochlorite is then removed in an exothermic reaction with thiosulfate ions, according to the following unbalanced reaction:

ClO– + S2O3 2– + OH– SO4 2– + Cl– + H2O

Propose a method that you could use experimentally to verify the stoichiometry of the balanced reaction, using common instruments used for students in a laboratory (N.B. Neither ion absorbs light in the visible region of the spectrum.)

Explanation / Answer

You can add silver nitrate in an acidic medium to identify chloride ions. By the amount of silver nitrate you can know the stochiometry of chloride ions produces. Once this value is known, you can calculate the moles of sulphate ions.

The precipitate formed between silver nitrate and chloride ions is white (silver chloride), make sure you know the concentration of silver added to the acidic solution you are about to test.