What is the minimum concentration of `Ba^(+2)` ions required in order to initiate the precipitation of `BaSO_(4)` from a solution containing 0.002 mole `L^(-1)` of ` So_(4)^(-2)` ions?
(Given `K_(sp)` for ` BaSO_(4)=1.4xx10^(-10))`

Explanation

If ionic product of `[Ba^(+2)][SO_(4)^(-2)]` is greater then `K_(sp)` for `Baso_(4),` then the precipitation occur. In a saturated solution
`[Ba^(+_2)]xx(2xx10^(-3))=1.4xx10^(-10)`
`[Ba^(+2)]=0.7xx10^(-7)mol L^(-1)`
Thus, minimum concentration of `Ba^(+2)` ions required for the precipitation of `BaSO_(4)` is `0.7xx10^(-7)` M.