Question

Compare water’s buffering capacity to that of the weak acid or base and explain why water’s buffering capacity is so much lower than the weak acid or base.

Answer 1

Handerson Hasselbach equation for a buffer solution,

pH = pKa + log ([conjugate base]/[acid])

In case of water, H₂O and OH- are equal in concentration and always exists in equilibrium. So, for water pH=pKa.

Therefore, if we add any acid or base to it will change its pH rapidly. So, its buffer capacity is less

On the contrary, for buffer, concentration of weak acid and its conjugate base are mixed in different proportion or concentration. Let’s assume if small amount of base is added to the solution then this added base will react with the acid untill all the acids are completed. Until then, it will resist the pH change. Same thing happens when acid is added. This is the reason for higher buffer capacity of buffer than water