Question

calculate pH of a ammonium chloride solution at a concentration of 0.1. Pkb of ammonia is 4.75​

Answer 1

Ammonium chloride is a salt of ammonium hydroxide (weak base) and hydrochloric acid (strong acid). Hence the solution is acidic in nature.

Given that the concentration of $\sf{NH_4Cl}$ is 0.1.

$\longrightarrow\sf{c=0.1}$

And given that $\sf{p^{k_b}}$ value of $\sf{NH_3}$ is 4.75.

$\longrightarrow\sf{p^{k_b}=4.75}$

The $\sf{p^H}$ value of the solution is given by,

$\longrightarrow\sf{p^H=7-\dfrac{1}{2}\left(\log c+p^{k_b}\right)}$

Then,

$\longrightarrow\sf{p^H=7-\dfrac{1}{2}\left(\log (0.1)+4.75\right)}$

$\longrightarrow\sf{p^H=7-\dfrac{1}{2}\left(-1+4.75\right)}$

$\longrightarrow\sf{p^H=7-\dfrac{1}{2}\times3.75}$

$\longrightarrow\sf{p^H=7-1.875}$

$\longrightarrow\sf{\underline{\underline{p^H=5.125}}}$

Hence $\sf{p^H}$ value of the $\sf{NH_4Cl}$ solution is $\bf{5.125.}$