Question

Calculate the pH of a solution prepared by dissolving 0.147 moles of acetic acid and 0.405 moles of sodium acetate in water sufficient to yield of solution. The Ka of acetic acid is 1.76*10-5

Answer 1

pH = 5.19

Step-by-step explanation:

Mixture of acetic acid with sodium acetate produce a buffer (Buffer is defined as the mixture of a weak acid with its conjugate base and vice versa). The pH of the buffer can be determined using Henderson-Hasselbalch equation:

pH = pKa + log₁₀ [A⁻] / [HA]

Where pKa is -log Ka = 4.75; [A⁻] is the concentration of conjugate base (Acetate ion) and [HA] is molar concentration of the weak acid.

-You can use moles of the compounds rather than its concentrations, that is:

[HA] = 0.147 moles

[A⁻] = 0.405 moles

Replacing in H-H equation:

pH = 4.75 + log₁₀ [0.405] / [0.147]

pH = 5.19