Question

For preparing a buffer solution of ph 6 by mixing sodium acetate and acetic acid the ratio of concentrations of salt and acid should be

Answer 1

Answer:

10:1

Explanation:

pH= pKa + log ([salt]/[acid])

pH= pKa+ log ([salt]/[acid])

$6 = - log({10}^{ - 5} ) + log \times \frac{(salt)}{(acid)}$

6=5+log ([salt]/[acid])

log ([salt]/[acid]) = 1

[salt]/[acid] = 10

Answer 2

Answer:

The ratio of concentrations of salt and acid should be 18.20:1.

Explanation:

To calculate the pH of acidic buffer, we use the equation given by Henderson Hasselbalch:

$pH=pK_a+\log(\frac{[salt]}{[acid]})$

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

Given : pH = 6

The dissociation constant of acid = $K_a=1.8\times 10^{-5}$

$pK_a=-\log[K_a]=-\log [1.8\times 10^{-5}]=4.74$

$6=4.74+\log(\frac{[CH_3COONa]}{[CH_3COOH]})$

$\frac{[CH_3COONa]}{[CH_3COOH]}=10^{6-4.74}$

$\frac{[CH_3COONa]}{[CH_3COOH]}=\frac{18.20}{1}$

The ratio of concentrations of salt and acid should be 18.20:1.