Page 69 - Modul Asam Basa

Contoh Soal

-1
+
[H ] = 1 x 10 M
+
pH = - log [H ]
pH = - log 10 M
-1

pH = 1

2. Tentukan pH larutan sebelum dan sesudah diencerkan dari 200 mL

larutan Mg(OH)2 0,1 M ditambah 200 mL air!

Jawab:
-
2+
Reaksi ionisasi: Mg(OH)2 (aq) → Mg (aq) + 2OH (aq)

Sebelum dilakukan pengenceran
[OH ] = x. Mb
-

-
-1
[OH ] = 2 x 0,1 x 10 M
- -2
[OH ] = 2 x 10 M
pOH = - log [OH ]
-

-2
pOH = - log 2 x 10 M

pOH = 2 – log 2
pH = 14 – (2 – log 2) = 12 + log 2

Setelah dilakukan pengenceran
V₁ × M₁ = V₂ × M₂

200 mL x 0,1 M = 400 mL x M2

20 M = 400 x M2
M2 = 0,05 M

-
[OH ] = x. Mb
- -2
[OH ] = 2 x 5 x 10 M
[OH ] = 1 x 10 M
-1
-

+
pOH = - log [H ]
-1
pOH = - log 10 M
pOH = 1

pH = 14 – 1 = 13

E-MODUL KIMIA ASAM BASA 57