Question

Calculate the pH of mixing 24 mL of 1M acetic acid with 76 mL of 1M sodium acetate. For the purpose of this calculation, assume the Ka of acetic acid is 1.8 X 10-5. You must include units to obtain full credit. You must show all your work to obtain any credit.

Answer 1

pH = 5.24

Step-by-step explanation:

Mixture of acetic acid with acetate ion is a buffer (Mixture of a weak acid with its conjugate base). The pH of a buffer can be determined using Henderson-Hasselbalch equation:

pH = pKa + log₁₀ [A⁻] / [HA]

Where pKa is -log Ka = 4.74; [A⁻] is the concentration of conjugate base (Acetate ion) and [HA] is molar concentration of the weak acid.

Concentration of the acetic acid in the 100mL≡0.1L (76mL + 24mL) solution is:

[HA] = 0.024L ₓ (1mol / L) / 0.1L = 0.24M

[A⁻] = 0.076L ₓ (1mol / L) / 0.1L = 0.76M

Replacing in H-H equation:

pH = 4.74 + log₁₀ [0.76M] / [0.24M]

pH = 5.24