Question

What is the pH at 25°C of a solution that results from mixing equal volumes of a 0.05 M solution of acetic acid and a 0.025 M solution of sodium hydroxide

Answer 1

when acetic acid and NaOH mixed then reaction is

CH3COOH + NaOH ..............> CH3COONa + H2O

let x L of of NaOH and x L of CH3COOH is mixed.

so x L of 0.05 M acetic acid = x * 0.05 = 0.05 x mole.

x L of 0.025 M NaOH =x * 0.025 = 0.025 x mole.

moles of salt = 0.025 x mole.

moles of acid = (0.05x - 0.025x) = 0.025x mole.

PKa of acetic acid = 4.74

Resulting solution is buffer solution.

Henderson equation is

PH = PKa + log [salt] / [acid]

PH = 4.74 + log (0.025x / 0.025x)

PH = 4.74 + log (1)

PH = 4.74