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

Buffers maintain a relatively constant pH because they consist of a weak acid and its conjugate base, which can neutralize added acids or bases. Adding acid to water causes a significant pH change, while the same is not true for buffer solutions. Examples include acetic acid and sodium acetate buffers, which show minimal pH changes upon acid or base addition.

Step-by-step explanation:

Understanding Buffers in Chemistry

When a few drops of a strong acid are added to water, the pH level dramatically decreases due to the increase in hydrogen ion concentration. This reaction changes the water's acidity substantially. For instance, the addition of 1.0 mL of 0.10 M hydrochloric acid to 1.0 L of pure water can change the pH from a neutral 7.0 to an acidic 4.0, a considerable shift. However, adding the same quantity of acid to a buffer solution does not cause a significant pH change.

A buffer is a special solution composed of a weak acid and its conjugate base or a weak base and its conjugate acid. The ability of a buffer to maintain a stable pH lies in its components' capacity to neutralize added acids or bases. An example of this is a solution containing acetic acid and sodium acetate in equal molar concentrations. Adding 10.0 mL of 1.0 M HCl to this buffer results in a pH change from 4.74 to only 4.73, showcasing the buffer's capacity to resist pH change despite the addition of a strong acid. This resistance is due to the reaction of H+ ions from the acid with the salt component of the buffer, preventing a significant increase in free H+ ion concentration in the solution.

In contrast, an unbuffered solution, such as distilled water, would experience major changes in pH upon the addition of the same amount of acid or base. The design of buffers is based on their concentration and the proper balancing of the weak acid and its conjugate base, which allows them to 'soak up' added H+ or OH- ions with minimal change to the overall pH level.

Answer 2

Buffers are resistant to high pH changes.

Step-by-step 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.