To 500 mL of 0.20 M acetic acid, solid NaOH (molar mass 40 g/mol) is added (no volume change) to obtain pH = $p K_{a} + 0.477$ ( $lo g 3 = 0.477$ ). Find the mass of NaOH in grams, to one decimal place.

Numerical answer type, answer in g, tolerance 0.1.

Answer: 3 g

Acid initially 0.10 mol. Let x mol NaOH be added: salt = x, acid = 0.10 - x.

lo g (x / (0.10 - x)) = 0.477

x / (0.10 - x) = 3

, x = 0.075 mol. Mass =

0.075 \times 40 = 3.0