Question

Find the pH of 0.10 M methylamine.

Short answer

The pH value for methylamine is 11.80

Step-by-step solution

Step 1: Define the term PH.                      

The negative logarithm of ${\mathbf{H}}^{\mathbf{+}}$ion concentration is used to calculate pH. As a result, the meaning of pH is justified as hydrogen power.

Calculate the ph.

0.10M methylamine

$$\begin{gathered} K_b=\frac{K_w}{K_a}=\frac{{10}^{-14}}{{10}^{-10.632}} \\ =4.3\times {10}^{-4} \end{gathered}$$

$$\begin{gathered} {\mathrm{K}}_{\mathrm{b}}=\frac{\left[{\mathrm{CH}}_3{\mathrm{NH}}_3{}^{+}\mathrm{H}_2\mathrm{O}\right]}{\left[{\mathrm{CH}}_3{\mathrm{NH}}_2\right]} \\ {\mathrm{K}}_{\mathrm{b}}=\frac{{\mathrm{x}}^2}{0.10-\mathrm{x}} \\ 4.3\times {10}^{-4}=\frac{{\mathrm{x}}^2}{0.10-\mathrm{X}} \end{gathered}$$

By using quadratic equation solve The value of x .

$x=6.78\times {10}^{-3}$

From the x value the is calculated as

$$\begin{gathered} \mathrm{pH}=-\log \left[{\mathrm{OH}}^{-}\right] \\ =-\log \left(6.78\times {10}^{-3}\right) \\ =2.17 \\ \mathrm{pH}+\mathrm{pOH}=14 \\ \mathrm{pH}=14-2.17=11.83 \end{gathered}$$

Thus the Ph value for methylamine is 11.8