What molar concentration of ammonia will provide a hydroxyl ion concentration of `1.5xx10^(-3)`? `(K_(b)=1.8xx10^(-5))`

Options

A. `0.125 M`
B. `0.12 M`
C. `0.13 M`
D. `0.14 M`

Answer

C

Explanation

The reaction is `NH_(3)+H_(2)OhArrNH_(4)^(+)+OH^(-)`
`K_(b)=1.8xx10^(-5)=([NH_(4)^(+)][OH^(-)])/([NH_(3)])`
`=((1.5xx10^(-3))(1.5xx10^(-3)))/([NH_(3)])=1.8xx10^(-5)`
Equilibrium conc. Of ammonia `[NH_(3)]=0.125 M`
And, total `[NH_(3)]=1.5xx10^(-3)+0.125=0.13 M`