What is the maximum concentration of equimolar solutions of ferrous sulphate and sodium sulphide so that when mixed in equal volumes, there is no precipitation of iron sulphide? (For iron sulphide, `K_(sp)=6.3xx10^(-18))`.

Explanation

`FeSO_(4)+Na_(2)Srarr FeS+Na_(2)SO_(4)`
Let V mL of a molar solution are mixed so that no precipitation of FeS is noticied. Let molarity of `FeSO_(4)` and `Na_(2)S` be a M.
Thus, `[Fe^(2+)][S^(2-)]=K_(SP)=6.3xx10^(-18)`
`[(axxV)/(2V)][(axxV)/(2V)]= 6.3xx10^(-18)`,
`a=5.02xx10^(-9)M`