Larutan 0,74 g ca(OH)2 (Mr = 74) dalam 2L air memiliki pH sekitar...?

Diketahui:
m = 0.74 g
v = 2 L
Mr Ca(OH)2 = 74

Ditanyakan:
pH = ....?

Dijawab:
n = m/Mr
n = 0.74/74
n = 0.01 mol

M = n/v
M = 0.01/2
M = 0.005 M atau 5 x 10^-3 M

Rx. ionisasi Ca(OH)2
Ca(OH)2 ---> Ca2^+ + 2OH^-

[OH-] = M x valensi basa
[OH-] = 5 x 10^-3 × 2
[OH-] = 10 x 10^-3

pOH = -log [OH-]
pOH = -log 10 x 10^-3
pOH = 3 - log 10

pH = Kw - pOH
pH = 14 - pOH
pH = 14 - (3-log 10)
pH = 11 + log 10

Jadi, pH larutan tsb adalah 11 + log 10.