Question

When you add base to a buffer, how do you calculate the new pH?

Answer 1

The new pH of a buffer solution after adding a base can be calculated using the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

where pH is the new pH of the buffer solution, pKa is the acid dissociation constant of the weak acid in the buffer, [A-] is the concentration of the conjugate base in the buffer, and [HA] is the concentration of the weak acid in the buffer.

To calculate the new concentration of the conjugate base [A-], you can use the following equation:

[A-] = [HA] * (pH - pKa)

where [HA] is the initial concentration of the weak acid in the buffer, pH is the new pH of the buffer solution, and pKa is the acid dissociation constant of the weak acid in the buffer.

Once you have calculated the new concentration of the conjugate base [A-], you can substitute it and the initial concentration of the weak acid [HA] into the Henderson-Hasselbalch equation to calculate the new pH.