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0.28 g of a commercial sample of K(2)Cr(...

0.28 g of a commercial sample of `K_(2)Cr_(2)O_(7)` was dissolved in water. Excess of KI was added to it along with dilute `H_(2)SO_(4)`. Iodine liberated was then titrated against sodium thiosulphate solution containing 24.82 g of `Na_(2)S_(2)O_(3). 5H_(2)O` per litre. The thiosulphate solution required was 50 mL. Find the percentage purity of the sample of `K_(2)Cr_(2)O_(7)`.

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The correct Answer is:
`87.5 %`
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0.5 gmixture of K_(2)Cr_(2)O_(7) and KMnO_(4) was treated with excess of KI in acidic medium. Iodine liberated required 150 cm^(3) of 0.10 N solution of thiosulphate solution for titration. Find trhe percentage of K_(2)Cr_(2)O_(7) in the mixture :

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