Question

A solution is prepared at that is initially in methylamine , a weak base with , and in methylammonium chloride . Calculate the pH of the solution. Round your answer to decimal places.

Answer 1

The question is incomplete, here is a complete question.

A solution is prepared at 25 °C that is initially 0.18 M in methylamine (CH₃NH₂), a weak base with $K_b=4.4\times 10^{-4}$, and 0.35 M in methylammonium bromide (CH₃NH₃Br). Calculate the pH of the solution. Round your answer to 2 decimal places.

Answer : The pH of the solution is, 10.36

Explanation :

First we have to calculate the value of $pK_b$.

$pK_b=-\log K_b$

$pK_b=-\log (4.4\times 10^{-4})$

$pK_b=3.35$

Now we have to calculate the value of pOH.

Using Henderson Hesselbach equation :

$pOH=pK_b+\log \frac{[Salt]}{[Base]}$

$pOH=pK_b+\log \frac{[CH_3NH_3Br]}{[CH_3NH_2]}$

Now put all the given values in this equation, we get :

$pOH=3.35+\log \frac{0.35}{0.18}$

$pOH=3.64$

Now we have to calculate the pH.

$pH+pOH=14\\\\pH=14-pOH\\\\pH=14-3.64=10.36$

Therefore, the pH of the solution is, 10.36