3.55g sample of bleaching powder suspended in $H_{2}O$ was  treated with $dil.H_{2}S{O}_4$ and $KI$ solution. Iodine thus liberated requires 80mL of 0.2 M hypo for titration. Calculate the % of available  chlorine in bleaching powder..

Bleaching powder + Acid + $Kl\to Kl3+$ starch (hypo) $\to$ end point (Blue $\to$ colourless)
 $\%{\text{\hspace{0.17em}\hspace{0.17em}of\hspace{0.17em}Cl}}_2=\frac{3.55\times \text{Molarity\hspace{0.17em}of hypo solution}\times mL\text{\hspace{0.17em}of hypo solution used intitration}}{W\left(\ln gm\right)}$
Moles of iodine = moles of chlorine  $=\frac{80\times 0.2}{2}\times {10}^{-3}=8\times {10}^{-3}$
Hence, required percentage $=\frac{8\times 71\times {10}^{-3}}{3.55}\times 100=16\%$