jika 300 ml CH3COOH 0,1 M dicampur dengan 200 ml NaOH 0,1 M (Ka = 2 x 10^-5). Maka pH larutkan yang dihasilkan adalah... A. 2 B. 3 C. 6 D. 4 E. 5

Materi : Larutan Buffer

[CH3COOH] = 0,1 M
V CH3COOH = 300 mL
[NaOH] = 0,1 M
V NaOH = 200 mL

n CH3COOH awal = M × V = 0,1 M × 300 mL = 30 mmol

n NaOH = M × V = 0,1 M × 200 mL = 20 mmol

......... CH3COOH + NaOH ===> CH3COONa + H2O ....
M ....... 30 mmol ...... 20 mmol ........ — ............... — .......
R ........- 20 mmol ...... - 20 mmol .... + 20 mmol .... + 20 mmol
S ......... 10 mmol ........ — ........... ...... 20 mmol ........ 20 mmol

n CH3COOH sisa = 10 mmol
n CH3COONa yg terbentuk = 20 mmol
Ka = 2 × 10^-5

[H+] = Ka × n CH3COOH sisa / n CH3COONa
[H+] = 2 × 10^-5 × 10 mmol / 20 mmol
[H+] = 10^-5

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

Jawaban : E . 5