Q.
The pH of which salt solution is independent of its concentration
$\left(\right.1\left.\right)$ $\left(\right.CH_{3}COO\left.\right)C_{5}H_{5}NH$
$\left(\right.2\left.\right)$ $NaH_{2}PO_{4}$
$\left(\right.3\left.\right)$ $Na_{2}HPO_{4}$
$\left(\right.4\left.\right)$ $NH_{4}CN$
NTA AbhyasNTA Abhyas 2022
Solution:
pH of amphoteric salts and weak acid weak base salt is independent of its concentration as they act like buffer.
The $pH$ Of the salts formed by weak acids and weak bases does not depend on the concentration of the salt.
$pH=7+\frac{1}{2}\left(\right.pKa-pKb\left.\right)$
$\left(\left(CH\right)_{3} COO\right)C_{6}H_{5}NH$ and $NH_{4}CN$ are salts of a weak acid and weak base.
The salt $\left(\left(CH\right)_{3} COO\right)C_{6}H_{5}NH$ is formed from weak acid acetic acid and weak base aniline.
The salt $NH_{4}CN$ is formed from $weakbaseNH_{4}OHandweakacidHCN$
The salts $NaH_{2}PO_{4}andNa_{2}HPO_{4}$ are formed from a weak acid $H_{3}PO_{4}$ and stong base $NaOH$ .
Both are amphoteric salts. Their $pH$ is the average of respective $pK_{a}$ values.
ex: $pH=\frac{pKa 1 + pKa 2}{2}$
Hence, their $pH$ is also independent of the concentration of the salts.
The $pH$ Of the salts formed by weak acids and weak bases does not depend on the concentration of the salt.
$pH=7+\frac{1}{2}\left(\right.pKa-pKb\left.\right)$
$\left(\left(CH\right)_{3} COO\right)C_{6}H_{5}NH$ and $NH_{4}CN$ are salts of a weak acid and weak base.
The salt $\left(\left(CH\right)_{3} COO\right)C_{6}H_{5}NH$ is formed from weak acid acetic acid and weak base aniline.
The salt $NH_{4}CN$ is formed from $weakbaseNH_{4}OHandweakacidHCN$
The salts $NaH_{2}PO_{4}andNa_{2}HPO_{4}$ are formed from a weak acid $H_{3}PO_{4}$ and stong base $NaOH$ .
Both are amphoteric salts. Their $pH$ is the average of respective $pK_{a}$ values.
ex: $pH=\frac{pKa 1 + pKa 2}{2}$
Hence, their $pH$ is also independent of the concentration of the salts.