Question

Dissociation constants of $CH_{3}COOH$ and $NH_{4}OH$ in aqueous solution are are almost same $\left(\right.10^{- 5}\left.\right)$ . If pH of a $CH_{3}COOH$ solution is 3, what will be the pH of $NH_{4}OH$ ?

• A. 3.0
• B. 4.0
• C. 10.0
• D. 11.0

Answer 1

Answer: (D)

pH of $CH_{3}COOH$
Sol $=3$
So $\left[\right.H_{3}O^{+}\left]\right.=\sqrt{c \times K_{a}}=10^{- 3}$
or $10^{- 3}=\sqrt{c \times 1 0^{- 5}}$
or $c=10^{- 1}$ M
$K_{b}=K_{a}=10^{- 5}$
pH of $10^{- 3}$ M
Solution of $NH_{4}OH$
$\left[\right.OH^{-}\left]\right.=\sqrt{c \times K_{b}}$
$=\sqrt{1 0^{- 1} \times 1 0^{- 5}}=10^{- 3}$
pOH $=3$
or $pH=14-3=11$