Question

Adding a few drops of a strong acid to water will lower the pH appreciably. However, adding the same number of drops to a buffer does not appreciably alter the pH.

Answer 1

Answer:

Buffers are resistant to high pH changes.

Explanation:

This perfectly explains the reason why we use buffers. Buffers are substances which consist of a weak acid and its conjugate base. Buffers are resistant to significant pH changes upon addition of strong acids or bases. To illustrate this, let's say we have a buffer consisting of 0.1 mol of HF, a weak acid, and 0.1 mol of NaF (fluoride is a conjugate base of HF).

• Let's say we add some strong acid, in a general form, this acid would be represented as $H_3O^+$. In this case, conjugate base will react and neutralize it to produce some amount of HF: $H_3O^+ (aq) + F^- (aq)\rightarrow HF (aq) + H_2O (l)$.
• Similarly, if we add some strong base $OH^-$, the acidic component will react with it to produce some amount of conjugate base: $HF (aq) + OH^- (aq)\rightarrow F^- (aq) + H_2O (l)$. The ratio of HF to NaF in this case is held around the same value for addition of small amounts of strong acids/bases, so pH is kept almost constant, while in neutral water, pH would drastically increase or decrease.