Question

One litre of a buffer solution has $0.13833$ mole of acetic acid and $0.1951$ mole of sodium acetate. Calculate $pH$ (nearest integer) of solution. Neglect volume change.

$K_a=1.8\times {10}^{-5}$. (log1.8 = 0.255)

Answer 1

First, calculate the pKa value.

$pKa=-logKa=-log1.8\times {10}^{-5}=4.75$

Now calculate the pH of the solution:

$pH=pKa+log\frac{sodiumacetate}{aceticacid}=4.75+log\left(\frac{0.1951}{0.13833}\right)$

$=4.75+0.1440=4.8940\approx 5$