1.25g of bleaching powder when treated with acetic acid and excess of KI, liberated iodine which required 37.5mL of 0.2N sodium thiosulphate solution. Calculate the percentage of available chlorine in the sample of bleaching powder.
A
30.0%
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B
21.3%
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C
12.5%
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D
9.7%
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Solution
The correct option is B21.3% CaOCl2(aq)+2CH3COOH(aq)→Ca(CH3COO)2+Cl2(g)+H2O(l) Cl2(g)+2KI(aq)→2KCl(s)+I2(g) I2(aq)+2Na2S2O3(aq)→Na2S4O6(aq)+2NaI(aq)
Equivalents of Na2S2O3= Equivalents of I2= Equivalents of Cl2 ∴Equivalents of Cl2=0.2×37.51000=0.0075 Amount of Cl2=0.0075×712=0.266g % of Cl2=0.2661.25×100%=21.3%