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

Answer:

Buffer 1.

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.