Question

State and explain the relative change in the pH and in the buffer-component concentration ratio, [NaA]/[HA], for each of the following additions:

(a) Add 0.1M NaOH to the buffer

(b) Add 0.1M HCl to the buffer

(c) Dissolve pure NaA in the buffer

(d) Dissolve pure HA in the buffer.

Short answer

1. The buffer component ratio will increase, and the pH will be raised by adding 0.1 M NaOH.
2. The buffer component ratio will decrease, and the pH of the buffer will be lowered by adding 0.1 M HCl.
3. The pH as well as the buffer component will rise.
4. The pH will drop due to the buffer component.

Step-by-step solution

Ionic Equilibrium

Ionic equilibrium refers to the equilibrium that exists in the solution of weak electrolytes between unionized molecules and ions.

(a) Add 0.1 M NaOH to the buffer

As, NaOH is a strong base, the additional${\mathrm{OH}}^{-}$ will react with HA to form NaA.

As a result, the NaA to HA ratio will rise.

When ${\mathrm{OH}}^{-}$interacts with HA, the HA is consumed, and the acid content in the solution is reduced.

Therefore, the buffer component ratio will rise on adding 0.1 M NaOH and it raises the pH.

(b) Add 0.1 M HCl to the buffer

As, HCl is a powerful acid, it will react with NaA to generate HA when ${\mathrm{H}}^{+}$ is introduced.

The ratio of NaA to HA will drop as a result.

When ${\mathrm{H}}^{+}$ combines with NaA, the base${\mathrm{A}}^{-}$ is consumed, lowering the solution's base concentration.

Therefore, the buffer component ratio will fall and adding 0.1 M HCl lowers the pH of the buffer.

(c) Dissolving pure NaA in buffer

When NaA is added to the buffer, the concentration of${\mathrm{A}}^{-}$ rises, resulting in a higher ratio of NaA to HA.

Also, because${\mathrm{A}}^{-}$ is a base, the buffer's total base concentration will rise, raising the pH of the solution.

Therefore, the buffer component as well as the pH will rise.

(d) Dissolving pure HA in buffer

When HA is added to the buffer, the concentration of HA rises, lowering the ratio of NaA to HA.

Also, because HA is an acid, the buffer's total acid content will rise, lowering the pH of the solution.

Therefore, both the buffer component and the pH will fall.