Question

The molarity of a buffer soultion made up from a weak acid and its conjugate base would be equal to:

• A. Molar concentration of weak acid only.
• B. Molar concentration of the conjugate base of the weak acid.
• C. Sum of the molar concentration of both the weak acid and its conjugate base.
• D. Net value obtained after deducting the molar concentration of conjugate base from the concentration of weak acid.

Hint:

The molarity of a buffer solution represents the total reservoir of active weak acid and conjugate base species available to buffer incoming hydronium or hydroxide ions.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
A buffer solution resists changes in pH when small amounts of an acid or a base are added. It consists of a mixture of a weak acid and its conjugate base.

Step 2: Detailed Explanation:
The total buffer concentration, often referred to as the analytical concentration or molarity of the buffer, is defined as the sum of the concentration of the weak acid species (\(\text{HA}\)) and its conjugate base species (\(\text{A}^-\)).
Mathematically: \[ C_{\text{buffer}} = [\text{HA}] + [\text{A}^-] \] When we speak of a "0.1 M acetate buffer", it means that the sum of the molar concentration of acetic acid and the molar concentration of acetate ions in the solution is 0.1 M, regardless of the individual ratios of the two species.

Step 3: Final Answer:
Therefore, the total molarity of the buffer is equal to the sum of the molar concentrations of both the weak acid and its conjugate base, as stated in option (C).