If `K_(sp)` of `Mg(OH)_(2)` is `1.2 xx 10^(-11)` . Then the highest pH of the 0.1 M solution of `Mg^(2+)` ion from which `Mg(OH)_(2)` is not precipitated is

Options

A. 4.96
B. 6.96
C. 7.54
D. 9.04

Answer

D

Explanation

`K_(sp)` of `Mg(OH)_(2)` is given by
`K_(sp)=[Mg^(2+)][OH^(-)]^(2)`
or `[OH^(-)]=K_(sp)//[Mg^(2+)]`
`=(1.2 xx 10^(-11))/(1xx10^(-1))=1.2 xx 10^(-10)`
`:. [OH^(-)]=1.1 xx 10^(-5)M`
`pOH =-log (1.1 xx 10^(-5))` or `5 - log (1.1)`
`=4.958`
`pH =14-4.958=9.04`