Calculate the pH of 0.375 L of a 0.18 M acetic acid–0.29 M sodium acetate buffer before and after the addition of (a) 0.0060 mol of KOH. Assume that the volume remains constant.

Verified step by step guidance

1. Identify the components of the buffer system: acetic acid (CH₃COOH) and sodium acetate (CH₃COONa).
2. Use the Henderson-Hasselbalch equation to calculate the initial pH of the buffer: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \( \text{pK}_a \) of acetic acid is approximately 4.76.
3. Calculate the moles of acetic acid and acetate ion in the buffer: \( \text{moles of CH}_3\text{COOH} = 0.375 \times 0.18 \) and \( \text{moles of CH}_3\text{COONa} = 0.375 \times 0.29 \).
4. Determine the effect of adding 0.0060 mol of KOH: KOH will react with acetic acid to form water and acetate ion, changing the moles of each component.
5. Recalculate the pH after the addition of KOH using the Henderson-Hasselbalch equation with the new concentrations of acetic acid and acetate ion.

Key Concepts

Buffer Solutions

Buffer solutions are mixtures that resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base, or a weak base and its conjugate acid. In this case, acetic acid (a weak acid) and sodium acetate (its conjugate base) form a buffer system that helps maintain a stable pH.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It is expressed as pH = pKa + log([A-]/[HA]), where pKa is the negative logarithm of the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid. This equation is essential for determining the pH before and after the addition of KOH.

Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to form water and a salt, resulting in a change in pH. In this scenario, the addition of KOH (a strong base) to the acetic acid buffer will neutralize some of the acetic acid, affecting the concentrations of the acid and its conjugate base. Understanding this reaction is crucial for calculating the new pH after the addition of KOH.