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Find the concentration of ion which is first precipitated at the point when the third ion starts precipitating, if $AgNO_3$ is added gradually to the solution that contains $0 .1\ M\ Cl^-, 0 .1\ M\ Br^-$ and $0. 1\ M\ I^-$
Given that
Salt || $K_{sp}$
$AgCl$ || $2 \times {10^{ - 10}}$
$AgBr$ || $5 \times {10^{ - 13}}$
$Ag$ || $9 \times {10^{ - 17}}$
$2.5 \times {10^{ - 3}}$
$4.5 \times {10^{ - 8}}$
$1.8 \times {10^{ - 4}}$
$5 \times {10^{ - 6}}$
Solution
$AgI$ will precipitate first, followed by $AgBr$ and $AgCl$. So, for precipitation of $Cl^-$
$\left[ {{\text{A}}{{\text{g}}^ + }} \right] \geqslant \frac{{2 \times {{10}^{ – 10}}}}{{0.1}}$
$ \simeq $ $2 \times 10^{-9}$
$\therefore [I^-] \leq \frac{9 \times 10^{-17}}{2 \times 10^{-9}} \simeq 4.5 \times 10^{-8}$
