Question

What is the pH of a 0.1 M phosphate buffer (pKa = 6.86) that contains equal amounts of acid and conjugate base?

Answer 1

Answer : The pH of a 0.1 M phosphate buffer is, 6.86

Explanation : Given,

$pK_a=6.86$

Concentration of acid = 0.1 M

Concentration of conjugate base (salt) = 0.1 M

Now we have to calculate the pH of buffer.

Using Henderson Hesselbach equation :

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

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

$pH=6.86+\log (\frac{0.1}{0.1})$

$pH=6.86$

Therefore, the pH of a 0.1 M phosphate buffer is, 6.86