Question

calculate the pH of a solution prepared by dissolving 2.05 g of sodium acetate, CH₃COONa, in 78.0 mL of 0.25 M acetic acid, CH₃COOH(aq). Assume the volume change upon dissolving the sodium acetate is negligible. k_a of CH₃COOH is 1.75 x 10^-5

Answer 1

$Moles~ of~ CH3COONa= ~\cfrac{2.05}{82.0} = ~0.025 ~mol$

$Volume~ V = 78.0 ~mL = 0.078~ L$

 $[CH_3COONa]=~ \cfrac{0.025}{0.078} = ~0.32~M$

$[CH_3COOH] = 0.25~ M$

$pH =~ -log(K_a) +~ log\bigg(\cfrac{[CH_3COONa]}{[CH_3COOH]}\bigg)$

$pH =~ -log(1.75 *~10^{-5}) + ~log\bigg(\cfrac{0.32}{0.25}\bigg) \\$

$pH= 4.757 + 0.079 = 4.836$

Answer: pH = 4,836