The solubility product $\left(\mathrm{K}_{\mathrm{sp}}ight)$ of $\mathrm{Fe}(\mathrm{OH})_{3}$ aqueous…

The solubility product $\left(\mathrm{K}_{\mathrm{sp}}ight)$ of $\mathrm{Fe}(\mathrm{OH})_{3}$ aqueous solution is $3.8 \times 10^{-38}$ at $298 \mathrm{~K}$. The solubility of $\mathrm{Fe}^{3+}$ ions will increase when
  1. Saturated solution is exposed to atmosphere
  2. $\mathrm{pH}$ is 7
  3. $\mathrm{pH}$ is decreased
  4. $\mathrm{pH}$ is increased

Solution

$\mathrm{Fe}(\mathrm{OH})_{3} ightleftharpoons \mathrm{Fe}^{3+}+3 \mathrm{OH}^{-}$
$\left[\mathrm{Fe}^{3+}ight]\left[\mathrm{OH}^{-}ight]^{3}=\mathrm{K}_{\mathrm{sp}}$. To increase $\left[\mathrm{Fe}^{3+}ight]$ $\left[\mathrm{OH}^{-}ight]$should decrease or $\left[\mathrm{H}^{+}ight]$will increase i.e., $\mathrm{pH}$ should decrease.

Asked in: JEE-TOPICTESTS-CHEMISTRY

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