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Q: A certain mass of sodium sulphate(IV) heptahydrate(Na2SO3.7H2O) was treated with 50cm3 of 0.12M iodine solution. The resulting solution was diluted to 200cm3 with 0.1M hydrochloric acid. 50cm3 of the solution was pipetted into conical flask and immediately titrated with 0.101M thiosulphate solution until the solution is pale yellow. Then about 100cm3 deionized water and 2cm3 starch solution were added and the titration was continued until the solution became just colourless. The volume of thiosulphate solution used was found to be 15cm3. Calculate the mass of sodium sulphate(IV)heptahydrate used intially. (Relative atomic masses: H:1, O:16, Na:23, S:32)
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