Question

If a buffer has an initial pH of 6.34 and the acid has a Ka of 3.46 × 10-4, what is the ratio of conjugate base to weak acid in the buffer system?

Answer 1

Answer: The ratio of conjugate base to weak acid in the buffer system is 758 : 1

Explanation:

The dissociation constant for  acid = $K_a=3.46\times 10^{-4}$

pH = 6.34

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:

$pK_a=-\log (3.46\times 10^{-4})$

$pK_a=3.46$

Now we have to calculate the ratio of conjugate base to weak acid in the buffer system

Using Henderson Hesselbach equation :

$pH=pK_a+\log \frac{[\text {conjugate base}]}{[Acid]}$

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

$6.34=3.46+\log \frac{[\text {conjugate base}]}{[Acid]}$

$\frac{[\text {conjugate base}]}{[Acid]}=758$

Therefore, the ratio of conjugate base to weak acid in the buffer system is 758: 1