Question

What is the minimum concentration of `SO_(4)^(2-)` required to precipitate `BaSO_(4)` in a solution containing `1.0 xx 10^(-4)` mol `Ba^(2+)` (`K_(sp)` for `BaSO_(4)` is `4 xx 10^(-10)`)
A. `4 xx 10^(-10)M`
B. `2 xx 10^(-7)M`
C. `4 xx 10^(-6)M`
D. `2 xx 10^(-3) M`

Answer 1

Correct Answer - C
`BaSO_(4) hArr Ba^(2+) + SO_(4)^(2-)`
`K_(sp) = S^(2) rArr S = sqrt(K_(sp)) , K_(sp) = [Ba^(2+)] xx [SO_(4)^(2-)]`
`4 xx 10^(-10) = [1 xx 10^(-4)] xx [SO_(4)^(2-)]`
`[SO_(4)^(2-)] = (4 xx 10^(-10))/(1 xx 10^(4)) = 4 xx 10^(-6)`.