Which of the following happens when NH 4 OH is added gradually to the solution containing 1 M A 2+ and 1 M B 3+ ions ? Given : K sp [ A ( OH ) 2 ]=9 × 10 -10 and K sp [ B ( OH ) 3 ]=27 × 10 -18 at 298 K .

B ( OH ) 3 will precipitate before A ( OH ) 2

A ( OH ) 2 and B ( OH ) 3 will precipitate together

A ( OH ) 2 will precipitate before B ( OH ) 3

Both A ( OH ) 2 and B ( OH ) 3 do not show precipitation with NH 4 OH

Chemistry · Ionic Equilibrium

JEE Main 2025 — 23 January, Morning Shift — Question 42

Which of the following happens when $\mathrm{NH}_{4} \mathrm{OH}$ is added gradually to the solution containing

$1 \mathrm{M} \mathrm{A}^{2+}$ and $1 \mathrm{M} \mathrm{B}^{3+}$ ions ?

Given : $\mathrm{K}_{\text {sp }}\left[\mathrm{A}(\mathrm{OH})_{2}\right]=9 \times 10^{-10}$ and

\mathrm{K}_{\mathrm{sp}}\left[\mathrm{~B}(\mathrm{OH})_{3}\right]=27 \times 10^{-18} \text { at } 298 \mathrm{~K} .

Option A:
$\mathrm{B}(\mathrm{OH})_{3}$ will precipitate before $\mathrm{A}(\mathrm{OH})_{2}$
Correct
Option B:
$\mathrm{A}(\mathrm{OH})_{2}$ and $\mathrm{B}(\mathrm{OH})_{3}$ will precipitate together
Option C:
$\mathrm{A}(\mathrm{OH})_{2}$ will precipitate before $\mathrm{B}(\mathrm{OH})_{3}$
Option D:
Both $\mathrm{A}(\mathrm{OH})_{2}$ and $\mathrm{B}(\mathrm{OH})_{3}$ do not show precipitation with $\mathrm{NH}_{4} \mathrm{OH}$

Condition for precipitation $\mathrm{Q}_{\mathrm{ip}}>\mathrm{K}_{\mathrm{sp}}$

For $\left[\mathrm{A}(\mathrm{OH})_{2}\right]$ $\left[\mathrm{A}^{2+}\right]\left[\mathrm{OH}^{-}\right]^{2}>9 \times 10^{-10}$

$\left[\mathrm{A}^{+2}\right]=1 \mathrm{M}$

$\Rightarrow\left[\mathrm{OH}^{-}\right]>3 \times 10^{-5} \mathrm{M}$ For $\left[\mathrm{B}(\mathrm{OH})_{3}\right]$

$\left[\mathrm{B}^{3+}\right]\left[\mathrm{OH}^{-}\right]^{3}>27 \times 10^{-18}$

$\left[\mathrm{B}^{3+}\right]=1 \mathrm{M}$

$\Rightarrow\left[\mathrm{OH}^{-}\right]>3 \times 10^{-6} \mathrm{M}$

$\mathrm{So}, \mathrm{B}(\mathrm{OH})_{3}$ will precipitate before $\mathrm{A}(\mathrm{OH})_{2}$

Answer key and solution verified before publishing.

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Exam: JEE Main 2025
Paper: 23 January, Morning Shift
Subject: Chemistry
Chapter: Ionic Equilibrium
Topic: Sparingly Soluble Salts, Solubility Product & Precipitation Conditions