Question

Which buffer would be better able to hold a steady pH on the addition of strong acid, buffer 1 or buffer 2? Explain. Buffer 1: a solution containing 0.10 M NH4Cl and 1 M NH3. Buffer 2: a solution containing 1 M NH4Cl and 0.10 M NH3

Answer 1

Buffer 1.

Step-by-step explanation:

Ammonia is a weak base. It acts like a Bronsted-Lowry Base when it reacts with hydrogen ions.

`\rm NH_3\; (aq) + H^(+)\; (aq) \to {NH_4}^(+)\; (aq)`.

`\rm NH_3` gains one hydrogen ion to produce the ammonium ion
`\rm {NH_4}^(+)`. In other words,
`\rm {NH_4}^(+)` is the conjugate acid of the weak base
`\rm NH_3`.

Both buffer 1 and 2 include

• the weak base ammonia
  `\rm NH_3`, and
• the conjugate acid of the weak base
  `\rm {NH_4}^(+)`.

The ammonia
`\rm NH_3` in the solution will react with hydrogen ions as they are added to the solution:

`\rm NH_3\; (aq) + H^(+)\; (aq) \to {NH_4}^(+)\; (aq)`.

There are more
`\rm NH_3` in the buffer 1 than in buffer 2. It will take more strong acid to react with the majority of
`\rm NH_3` in the solution. Conversely, the pH of buffer 1 will be more steady than that in buffer 2 when the same amount of acid has been added.