Question

A buffer solution is prepared from equal volumes of 0.200 M acetic acid and 0.600 M sodium acetate. Use 1.80 × 10⁻⁵ as Ka for acetic acid. Calculate the pH of the buffer.

Answer 1

To determine the pH of the buffer solution created from equal volumes of 0.200 M acetic acid and 0.600 M sodium acetate, use the Henderson-Hasselbalch equation. The pH calculated using the given acid dissociation constant (Ka) is approximately 5.22, which means the buffer is weakly acidic.

Step-by-step explanation:

To calculate the pH of a buffer solution prepared from equal volumes of 0.200 M acetic acid and 0.600 M sodium acetate, we can use the Henderson-Hasselbalch equation:

pH = pKa + log ([A-]/[HA])

Where [A-] is the concentration of the acetate ion and [HA] is the concentration of acetic acid. Since we have equal volumes of the acetic acid and acetate, we can simply use their initial concentrations in the equation. With the acetic acid's dissociation constant (Ka) of 1.80 × 10⁻⁵, the pKa can be calculated as follows:

pKa = -log(Ka) = -log(1.80 × 10⁻⁵) ≈ 4.74

Using our concentrations:

pH = pKa + log ([0.600]/[0.200])
pH = 4.74 + log (3)
pH ≈ 4.74 + 0.477 ≈ 5.217

Therefore, the pH of the buffer solution is approximately 5.22, indicating the solution is weakly acidic.