What is the pH of a buffer solution when the concentrations of both buffer components (the weak acid and its conjugate base) are equal? What happens to the pH when the buffer contains more of the weak acid than the conjugate base? More of the conjugate base than the weak acid?

Considering the Henderson - Hasselbalch equation for the calculation of the pH of the buffer solution as:

pH=pKa+log[base]/[acid]

When the the concentrations of both buffer components (the weak acid and its conjugate base) are equal:

[base] = [acid]

So, pH=pKa+log1 = pKa

pH is equal to pKa of weak acid of buffer system.

When buffer contains more of weak acid than conjugate base:

[base] < [acid]

log [base]/[acid] = Negative,

So,

When more of acid component is present, the pH is more acidic. (It decreases)

When buffer contains more of conjugate base than weak acid:

[base] > [acid]

log [base]/[acid] = Positive,

So,

When more of acid component is present, the pH is more acidic. (It increases)