Question

A buffer is made by mixing 100 mL of 0.25 M acetic acid (CH3COOH) and 150 mL of 0.10 M sodium acetate (CH3COONa). Calculate the pH of the solution after 0.5g of solid NaOH is added to the solution (Given Ka (CH3COOH) =1.8 x 10-5)

Answer 1

millimols HAc (CH3COOH) = mL x M = 25
mmols NaAc(CH3COONa) = 15
mmols NaOH = mg/molar mass = 12.5
----------------------------

.......HAc + OH^- ==> Ac^- + H2O
I......25....0.......15........
add.........12.5...................
C...-12.5..-12.5.....12.5.........
E.....12.5...0.......27.5

Substitute the E line into the Henderson-Hasselbalch equation and calculate pH.

Answer 2

19.5