Magnesium is not precipitated from a solution of its salt by `NH_(4)OH` in the presence of `NH_(4)CI.` Explain.

Explanation

`Mg^(2+)` ions present in its salt solution are to be precipitated as `Mg(OH)_(2)` on adding `NH_(4)OH.` But the presence of `NH_(4)CI` will suppress the ionisation of `NH_(4)OH` due to common ion effect. As a result ionic product of `Mg^(2+)` and `OH^(-)` ions will remian less than the `K_(sp)` value of `Mg(OH)_(2)`. It will not be, therefore, precipitated.
`NH_(4)OH overset((aq))(hArr) NH_(4)^(+) (aq) + OH^(+) (aq)`
`NH_(4)CI overset((aq))(to) NH_(4)^(+) (aq) +CI^(-) (aq)`