Question

What minimum concentration of $SO_{4}^{2 -}$ is required to precipitate $BaSO_{4}$ from the solution containing $1.0\times 10^{- 4 \, }moles of \, Ba^{2 +}$ ? (Given $K_{s p}$ for $BaSO_{4}$ is $4\times 10^{- 10}$ )

• A. $2\times 10^{- 3}M$
• B. $2\times 10^{- 7}M$
• C. $4\times 10^{- 6}M$
• D. $4\times 10^{- 10}M$

Answer 1

Answer: (C)

$BaSO_{4}$ ⇌ $Ba^{2 +}+SO_{4}^{2 -}$

$K_{s p}=\left[\right.Ba^{2 +}\left]\right.\times \left[\right.SO_{4}^{2 -}\left]\right.$

$K_{s p}=S^{2}\Rightarrow S=\sqrt{K_{s p}}$ ;

$4\times 10^{- 10}=\left[\right.1\times 10^{- 4}\left]\right.\times \left[\right.SO_{4}^{2 -}\left]\right.$

$\left[\right.SO_{4}^{2 -}\left]\right.=\frac{4 \times 1 0^{- 10}}{1 \times 1 0^{- 4}}=4\times 10^{- 6}$ .