Question:
Arrange the following solutions in the decreasing order of pOH:
(A) $0.01 \mathrm{M} \mathrm{HCl}$
(B) $0.01 \mathrm{M} \mathrm{NaOH}$
(C) $0.01 \mathrm{M} \mathrm{CH}_{3} \mathrm{COONa}$
(D) $0.01 \mathrm{M} \mathrm{NaCl}$
Correct Option: , 2
Solution:
(A) $0.01 \mathrm{MHCl}$
$\left[\mathrm{H}^{+}\right]=10^{-2}, \mathrm{pH}=-\log 10^{-2}=2$
$\mathrm{pOH}=14-2=12$
(B) $0.01 \mathrm{MNaOH}$
$\left[\mathrm{OH}^{-}\right]=10^{-2}, \mathrm{pOH}=-\log [\mathrm{OH}]=2$
(C) $0.01 \mathrm{M} \mathrm{CH}_{3} \mathrm{COONa}$
$\mathrm{pH}=7+\frac{1}{2}\left[\mathrm{p} K_{\mathrm{a}}+\log 0.01\right]$
(D) $0.01 \mathrm{M} \mathrm{NaCl}, \mathrm{pH}=7, \mathrm{pOH}=7$
Decreasing order of $\mathrm{pOH}$ value is,
$(\mathrm{A})>(\mathrm{D})>(\mathrm{C})>(\mathrm{B})$.