Question

What is the pH of millimolar solution of ammonium hydroxide which is 20% dissociated?

• A. $3.699$
• B. $10.301$
• C. $4.691$
• D. $9.301$

Answer 1

The correct option is D $9.301$

Concentration of $N{H}_{4}OH$ solution $=0.001M$

Degree of dissociation $=20$% $=\frac{20}{100}=0.2$

Concentration of $O{H}^{-}$ i.e., $\left[O{H}^{-}\right]=$ Concentration of solution $\times$ degree of dissociation

$=0.001\times 0.02=2\times {10}^{-5}$

$\because \left[H^{+}\right]\left[O{H}^{-}\right]=1\times {10}^{-14}$

$\therefore \left[H^{+}\right]=\frac{1\times {10}^{-14}}{2\times {10}^{-5}}=5\times {10}^{-10}$

Again, $\because pH=-\log \left[H^{+}\right]$

$\therefore pH=-\log (5\times {10}^{-10})$

$=10-0.3010=9.3010$