Question

$20mL$ of $0.02M$ hypo solution is used for the titration of $10mL$ of copper sulphate solution, in the presence of excess of KI using starch as an indicator. The molarity of $C{u}^{2+}$ is found to be______ $\times 10^{-2}M$ [nearest integer]
Given : $2C{u}^{2+}+4I^{-}\to C{u}_2{I}_2+I_2$
$I_2+2S_2{O}_3{}^{2-}\to 2I^{-}+S_4{O}_6{}^{2-}$

Answer 1

Answer: 4

$n_{\text{eq. }}\text{ of }{I}_2=n_{eq}\text{ of }N{a}_2{S}_2{O}_3=20\times 0.002\times 1$
$2\times n_{mol}\text{ of }{I}_2=0.4$
$n_{mol}\text{ of }{I}_2=0.2mmol$
$n_{mol}\text{ of }C{u}^{+2}=0.2\times 2\times 10^{-3}$
$\left[C{u}^{+2}\right]=\frac{0.4\times 10^{-3}}{10\times 10^{-3}}=0.04=4\times 10^{-2}$