larutan NaX 0.04 mempunyai pH =8+log 2. Harga Ka HX adalah

pH = 8 +log 2
pOH = 14 - 8 + log 2 = 6 - log 2
OH¯ = 2.10¯6

[OH¯]² = Kw/Ka x [M]
(2.10¯6)² = 10¯¹⁴ / Ka x (4.10¯²)
Ka = 4.10¯16 / 4.10¯¹²
= 1.10¯⁴