Question

What is the $O{H}^{-}$ concentration of a 0.08 M solution of $C{H}_{3}COONa$?

[$K_a\left(C{H}_{3}COOH\right)=1.8\times {10}^{-5}$]

Answer 1

$C{H}_{3}COONa$ is formed from $C{H}_{3}COOH$ and $NaOH$ , i.e., weak acid and strong base. Salt hydrolysis of $C{H}_{3}COONa$ gives:

$⟹pH=7+\frac{1}{2}p{K}_a+\frac{1}{2}\log C⟹pH=7+\frac{1}{2}(5-\log \left(1.8\right))+\frac{1}{2}\log \left(0.08\right)⟹pOH=14-(7+\frac{1}{2}(5-\log \left(1.8\right))+\frac{1}{2}\log \left(0.08\right))=5-\log \left(0.669\right)⟹\left[O{H}^{-}\right]=0.669\times {10}^{-5}M$