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)S to FeS+Na_(2)SO_(4)`
Let V mL of a molar solution are mixed so that no precipitation of FeS is noticed. Let molarity of `FeSO_4 and Na_2S` be a M.
Thus, `[Fe^(2+)] [S^(2-)]=K_(SP)=6.3 xx 10^(-18)`
`[(a xx V)/(2V)] [(a xx V)/(2V)]=6.3 xx 10^(-18)`
`therefore a=5.02 xx 10^(-9)M`