Sebanyak 8gram cuplikan mengandung Ca(OH)2 di larutkan di dalam 250 ml air. jika ph larutan tersebut 12+log 2. Hitung kadar Ca(OH)2 , Ar. Ca =40 ; O =16 ; H =1

Diketahui :
m sampel = 8 g
v = 250 mL = 0,25 L
pH = 12 + log 2

Ditanya :
%Ca(OH)₂ ?

Jawab:
pOH = pKw - pH
pOH = 14 - (12 + log 2)
pOH = 14 - 12 - log 2
pOH = 2 - log 2

[OH⁻] = 2 × 10⁻² M

Ca(OH)₂ → Ca²⁺ + 2 OH⁻
[Ca(OH)₂] = 1/2 × [OH⁻]
[Ca(OH)₂] = 1/2 × 2 × 10⁻² M
[Ca(OH)₂] = 10⁻² M

n Ca(OH)₂ = 10⁻² M × 0,25 L
n Ca(OH)₂ = 2,5 × 10⁻³ mol

Mr Ca(OH)₂ = 40 + ( 2 × 16) + (2 × 1) = 74 g/mol

m Ca(OH)₂ = n Ca(OH)₂ × Mr Ca(OH)₂
m Ca(OH)₂ = 2,5 × 10⁻³ mol × 74 g/mol
m Ca(OH)₂ = 0,185 g

% Ca(OH)₂ = [tex] \frac{m Ca(OH)2}{m sampel} [/tex] × 100%
% Ca(OH)₂ = [tex] \frac{0,185 g}{8 g} [/tex] × 100%
% Ca(OH)₂ = 2,3125%