A buffer contains 0.10 mol of acetic acid and 0.13 mol of sodium acetate in 1.00 L. (b) What is the pH of the buffer after the addition of 0.02 mol of KOH?

Verified step by step guidance

1. Identify the components of the buffer system: acetic acid (CH₃COOH) and sodium acetate (CH₃COONa).
2. Recognize that the addition of KOH, a strong base, will react with the acetic acid in the buffer.
3. Write the chemical equation for the reaction: CH₃COOH + OH⁻ → CH₃COO⁻ + H₂O.
4. Calculate the moles of acetic acid and acetate after the reaction with KOH. Subtract the moles of KOH from the moles of acetic acid and add the moles of KOH to the moles of acetate.
5. Use the Henderson-Hasselbalch equation to find the new pH: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{CH}_3\text{COO}^-]}{[\text{CH}_3\text{COOH}]} \right) \), where \( \text{pK}_a \) is the negative logarithm of the acid dissociation constant of acetic acid.

Key Concepts

Buffer Solutions

A buffer solution is a system that resists changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base, which work together to neutralize added acids or bases. In this case, acetic acid (weak acid) and sodium acetate (conjugate base) form a buffer that can maintain pH stability.

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 after the addition of KOH.

Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to form water and a salt, effectively reducing the concentration of both species. In this scenario, the addition of KOH (a strong base) will react with acetic acid, decreasing its concentration while increasing the concentration of acetate ions. Understanding this reaction is crucial for calculating the new pH of the buffer.