Question

What is the minimum concentration of $B{a}^{+2}$ ions required in order to initiate the precipitation of $BaS{O}_4$ from a solution containing $0.002mol{L}^{-1}$ of $S{O}_4^{-2}$ ions?
(Given $K_{sp}$ for $BaS{O}_4=1.4\times {10}^{-10}$ )

• A. $1.7\times {10}^{-7}M$
• B. $2.7\times {10}^{-7}M$
• C. $7.0\times {10}^{-8}M$
• D. $7.0\times {10}^{-10}M$

Answer 1

The correct option is C $7.0\times {10}^{-8}M$

If ionic product of $\left[B{a}^{+2}\right]\left[S{O}_4^{-2}\right]$ is greater than $K_{sp}$ for $BaS{O}_4,$ then the precipitation occur.
$\left[B{a}^{+2}\right]\left[S{O}_4^{-2}\right]>1.4\times {10}^{-10}$
In a saturated solution
$\left[B{a}^{+2}\right]\times (2\times {10}^{-3})=1.4\times {10}^{-10}$
$\left[B{a}^{+2}\right]=0.7\times {10}^{-7}mol{L}^{-1}$
Thus, minimum concentration of $B{a}^{+2}$ ions required for the precipitation of $BaS{O}_4$ is $0.7\times {10}^{-7}M$.