Question

40 mL of 0.2 M \( \mathrm{CH_3COOH} \) is titrated with 0.2 M NaOH solution. How many mL of NaOH should be added to form a buffer solution with maximum buffer capacity?

• A. 20 mL
• B. 40 mL
• C. 10 mL
• D. 5 mL

Hint:

The maximum buffer capacity occurs when the concentration of a weak acid and its conjugate base are equal.

Answer 1

The Correct Option is A

Step 1: Understanding buffer formation and maximum buffer capacity.

A buffer solution with maximum buffer capacity is formed when the concentration of weak acid (\( \text{CH}_3\text{COOH} \)) and its conjugate base (\( \text{CH}_3\text{COO}^- \)) are equal. This occurs at the half-equivalence point of the titration.

Step 2: Calculating the required NaOH volume.
Given volume of \( \text{CH}_3\text{COOH} \) = \( 40 \) mL
Given molarity of \( \text{CH}_3\text{COOH} \) = \( 0.2 \) M
Moles of \( \text{CH}_3\text{COOH} \) = \[ 40 \times 0.2 \div 1000 = 0.008 \, \text{moles} \] The half-equivalence point occurs when half of the acid has been neutralized.
Thus, required moles of NaOH = \( \frac{0.008}{2} = 0.004 \) moles.
Since the molarity of NaOH is 0.2 M, the required volume is: \[ V = \frac{0.004}{0.2} \times 1000 = 20 \, \text{mL}. \]

Thus, the volume of NaOH required to form a buffer solution with maximum buffer capacity is 20 mL.