Q30 / 180 · COMEDK 2018 · Chemistry

Solubility product of a salt $A B$ is $1 \times 10^{-8} \mathrm{M}^{2}$ in a solution in which the concentration of $A^{+}$ions is $10^{-3} \mathrm{M}$. The salt will precipitate when the concentration of $B^{-}$ions is kept

  • A
    between $10^{-8} \mathrm{M}$ to $10^{-7} \mathrm{M}$
  • B
    between $10^{-7} \mathrm{M}$ to $10^{-6} \mathrm{M}$
  • Correct answer
    C
    $>10^{-5} \mathrm{M}$
  • D
    $ < 10^{-8} \mathrm{M}$

Solution

$$ \begin{aligned} K_{\mathrm{sp}} &=10^{-8} \mathrm{M}^{2} \\ K_{\mathrm{sp}} &=\left[A^{+}\right]\left[B^{-}\right] \\ 10^{-8} &=\left(10^{-3}\right)\left[B^{-}\right] \\ {\left[B^{-}\right] } &=10^{-5} \mathrm{M} \end{aligned} $$ $\therefore$ Salt will precipitate, when concentration of $\left[B^{-}\right]>10^{-5} \mathrm{M}$.

Hence, the correct answer is option: 'C'.

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