What will happen to the pH of (M/10) NH4CN solution on dilution?

Question

What will happen to the pH of (M/10) NH4CN solution on dilution? (A) Increases. (B) Decreases. (C) Remains same. (D) Initially it increases, then decreases.

Tardigrade Admin · Accepted Answer

NH 4 CN is a salt of weak acid and weak base. To calculate its pH, we have, pH =(1/2)( pK w + pK a - pK b ) We can see that pH is independent of concentration. Hence, further dilution would not affect it and thus remains same.

Q. What will happen to the $p H$ of $\frac{M}{10}$ $N H_{4} CN$ solution on dilution?

Increases.

Decreases.

Remains same.

Initially it increases, then decreases.

$N H_{4} CN$ is a salt of weak acid and weak base.
To calculate its $p H$ , we have,
$p H = \frac{1}{2} (p K_{w} + p K_{a} - p K_{b})$
We can see that $p H$ is independent of concentration. Hence, further dilution would not affect it and thus remains same.

Q. What will happen to the pH of 10M​ NH4​CN solution on dilution?