Question

What will happen if the pH of the solution of $0.001$M $Mg(N{O}_3{)}_2$ solution is adjusted to $pH=9$?

[Given that : $K_{sp}$ of $Mg(OH{)}_2=8.9\times {10}^{-12}$)].

• A. ppt will take place
• B. ppt will not take place
• C. solution will be saturated
• D. none of the above

Answer 1

The correct option is B ppt will not take place

At $pH=9,pOH=14-pH=5$ and $\left[O{H}^{-}\right]={10}^{-5}M$

In a $0.001M$ solution of $Mg(N{O}_3{)}_2$,

$\left[M{g}^{+2}\right]=0.0010M$

The ionic product for $Mg(OH{)}_2=[Mg]\times [O{H}^{-}{]}^2=0.0010\times ({10}^{-5}{)}^2=1\times {10}^{-13}{M}^3$

which is smaller than the $Ksp$ of $8.9\times {10}^{-12}{M}^3$

So, we don't see a ppt at this pH.