Calculate the pH of the resultant solution of mixing together two solutions of 2 L of 1.0 M acetic acid, 0.5 L of 1.0 M sodium acetate and then adding 8 g of solid NaOH (MW = 40.0 g/mole).

Answer 1

Find starting # of moles of acid & base
(2L)(1M) = 2 moles HA
(.5L)(1M)= .5 moles A

Add 8 g NaOH
Convert grams to mole
8g (1mol/40g) = .2 moles NaOH

Find resulting # of moles
2 mol - .2 mol = 1.8 mol HA
.5 mol + .2 mol = .7 mol A

Use Henderson–Hasselbalch equation to find pH. pKa of acetic acid is 4.77

pH = pKa + log (A/HA)
pH = 4.77 + log (.7/1.8)
pH = 4.36

Your answer is 4.36!