Question

Find the pH when V_a = 14.63 mL.

Short answer

The pH is 4.73

Step-by-step solution

Information given

The following information was obtained from the example to solve this problem

Titration of pyridine using HCl

Amount of pyridine=25.00 mL of 0.08364M pyridine

Concentration of HCl=0.1067 M

Equivalence point occurs at 19.60 mL

pK_a =5.20

K_b = 1.59×10^-9

K_a=(K_w/K_b)=6.31×10^-6

Reaction

The titration reaction is as follows

In the mixture of pyridine and pyridinium ion, a part of pyridine will be neutralized.

Calculation

The fraction of pyridine titrated is (14.63/19.60)=0.746

Therefore, the remaining fraction will be

1-0.746=0.254

The pH will be

$\begin{array}{rcl}pH& =& p{K}_a+\log \left(\frac{B}{B{H}^{+}}\right)\\ & =& 5.20+\log \left(\frac{0.254}{0.746}\right)\\ & =& 4.73\end{array}$

Therefore, the pH is 4.73