Question

Question 2 Calculate the pH of a solution that has an acetic acid concentration of 0.05 M and a sodium acetate concentration of 0.075 M. (a) By making use of the Henderson - Hasselbach equation. (b) Without making any assumptions. (4) (6) 1101

Answer 1

Answer : The pH of the solution is, 4.9

Explanation : Given,

Dissociation constant for acetic acid = $K_a=1.8\times 10^{-5}$

Concentration of acetic acid = 0.05 M

Concentration of sodium acetate = 0.075 M

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

The expression used for the calculation of $pK_a$ is,

$pK_a=-\log (K_a)$

Now put the value of $K_a$ in this expression, we get:

$pK_a=-\log (1.8\times 10^{-5})$

$pK_a=5-\log (1.8)$

$pK_a=4.7$

Now we have to calculate the pH of buffer.

Using Henderson Hesselbach equation :

$pH=pK_a+\log \frac{[Salt]}{[Acid]}$

$pH=pK_a+\log \frac{[CH_3COONa]}{[CH_3COOH]}$

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

$pH=4.7+\log (\frac{0.075}{0.05})$

$pH=4.9$

Therefore, the pH of the solution is 4.9.