Question

10 g of bleaching powder on reaction with KI required 100 mL of 1 N hypo. Thus, % of pure bleaching powder is :

• A. 100 %
• B. 80 %
• C. 63.5 %
• D. 35.5 %

Answer 1

The correct option is C 63.5 %

Balanced reaction:
$CaOC{l}_2+2KI+H_{2}S{O}_4\to I_2+CaC{l}_2+H_{2}O+K_{2}S{O}_4$
1 2 1
$I_2+2S_2{O}_3^{2-}\to S_4{O}_6^{2-}+2I^{-}$
1 2
No. of moles of hypo solution is 0.1 mole, so moles of bleaching powder in reaction is $0.05$ mole $=0.05\times 127=6.35$gm.
So % purity of solution is 63.5%.