Berapakah massa CH3COONa yang harus ditambahkan ke dalam 1 liter larutan CH3COOH 0,1 M agar diperoleh PH larutan = 5. (Mr CH3COONa = 82, Ka CH3COOH = 10^-5)

CH3COONa + 1 L CH3COOH 0,1 M
Mr CH3COONa = 82
Ka CH3COOH = 10^-5
pH = 5

massa CH3COONa ... ?

pH = 5
- log [H^+] = 5
[H+] = 10^-5

n CH3COOH = M × V
n CH3COOH = 0,1 × 1
n CH3COOH = 0,1 mol

[H^+] = Ka × n Asam lemah/n B. konjugasi
10^-5 = 10^-5 × 0,1 / n CH3COONa
1 = 0,1 / n CH3COONa
n CH3COONa = 0,1 mol

n CH3COONa = massa/Mr
................... 0,1 = massa/82
.......... 82 × 0,1 = massa
................. 8,2 = massa
............ massa = 8,2 gram

Jadi, massa CH3COONa yang harus ditambahkan adalah 8,2 gram.