Question

Prepare a solution that is 0.1 M acetic acid and 0.1 M sodium acetate by measuring out 5.0 mL of the 1.0 M acetic acid solution and 5.0 mL of the 1.0 M sodium acetate solution in a 100 mL graduated cylinder, diluting the 10.0 mL to a final volume of 50.0 mL with deionized water, and then stirring. Pour this solution into a clean, dry 100 mL breaker. By knowing that the Ka for acetic acid is 1.8 x -5 10 , calculate the theoretical pH of the solution.

Answer 1

Answer:

4.74

Explanation:

It is possible to find pH of a buffer (The mixture of a weak acid: Acetic acid, with its conjugate base: Sodium acetate) using Henderson-Hasselbalch equation:

pH = pKa + log₁₀ [A⁻] / [HA]

Where pKa is -log Ka of the weak acid,  [A⁻] concentration of the conjugate base and [HA] concentration of the weak acid

pKa of acetic acid is -log 1.8x10⁻⁵ = 4.74

The concentration of both, acetic acid and sodium acetate is 0.1M. Replacing in H-H equation:

pH = pKa + log₁₀ [A⁻] / [HA]

pH = 4.74 + log₁₀ [0.1] / [0.1]

pH = 4.74 + log₁₀ 1

pH = 4.74

Theoretical pH is 4.74