Define buffer' and 'buffer capacity'. Calculate the pH of buffer which is 0.2 M with respect to CH,COOH and 0.1 M with respect to CH, COONa. Given that, k = 1.75 x 10 for acetic acid.

Answer 1

Definitions:

1. Buffer: A buffer is a solution that resists changes in pH when small amounts of an acid or base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

2. Buffer Capacity: Buffer capacity refers to the ability of a buffer solution to resist changes in pH upon the addition of acids or bases. It is usually quantified as the amount of strong acid or base that can be added to a buffer system before a significant change in pH occurs.

Given Data for the Calculation:

• Concentration of acetic acid (CH₃COOH) = 0.2 M
• Concentration of sodium acetate (CH₃COONa) = 0.1 M
• Acid dissociation constant for acetic acid (K_a) = 1.75 x 10⁻¹⁰

Step 1: Calculate pKa

To calculate the pH of the buffer solution using the Henderson-Hasselbalch equation, we first need to calculate \(pK_a\):

\[ pK_a = -\log(K_a) \]

Substituting the given \(K_a\):

\[ pK_a = -\log(1.75 \times 10^{-5}) \approx 4.75 \]

Step 2: Use the Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is given by:

\[ pH = pK_a + \log\left(\frac{[\text{A}^-]}{[\text{HA}]}\right) \]

where:

• \([\text{A}^-]\) is the concentration of the conjugate base (sodium acetate, CH₃COONa).
• \([\text{HA}]\) is the concentration of the weak acid (acetic acid, CH₃COOH).

Step 3: Substitute Values

Substituting the given concentrations into the equation:

\[ pH = pK_a + \log\left(\frac{[0.1]}{[0.2]}\right) \] \[ pH = 4.75 + \log(0.5) \] \[ \log(0.5) \approx -0.301 \]

Substituting back into the pH equation:

\[ pH = 4.75 - 0.301 \approx 4.449 \]

Final Result:

The pH of the buffer solution is approximately 4.45.