Question

Which one of the following solutions will have the highest pH value?

• A. $0.01M$ $NaOH$
• B. $0.02M$ ${CH}_{3}COONa$
• C. $0.01M$ $NaH{CO}_3$
• D. $0.01M$ $H_2{SO}_4$

Answer 1

The correct option is A $0.01M$ $NaOH$

(A) $0.01M$ $NaOH$

$\therefore pH=14-pOH=14-(-\log {10}^{-2})=12$

(B) $0.02M$ $C{H}_{3}COONa$

This is a salt of weak acid and strong base.

$pH=7+1/2p{K}_a+1/2\log C$

$=7+1/2\times 4.74+1/2\log ({10}^{-2}\times 2)=8.5$

(C) $0.01M$ $NaHC{O}_3$

$pH=\frac{1}{2}p{K}_1+\frac{1}{2}p{K}_2=\frac{1}{2}(-\log 4\times {10}^{-7}-\log 6\times {10}^{-11})$

$=8.3$

(D) $0.01M$ $H_{2}S{O}_4$ $H_{2}S{O}_4\rightleftharpoons 2H^{+}+S{O}_4^{2-}$

$\therefore \left[H^{+}\right]=2\times 0.01=0.02M$

$\therefore pH=-\log \left(0.02\right)=1.69$

Therefore, $0.01M$ $NaOH$ solution has highest $pH$ .