Page 69 - Modul Asam Basa Kelas XI

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 0,01 M ditambah 200 mL air!
Jawab:

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

Sebelum dilakukan pengenceran

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

[OH ] = 2 x 10 M
-2
-

-
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 0,01 M = 400 mL x M2

2 M = 400 x M2
M2 = 0,005 M

-
[OH ] = x. Mb
-3
-
[OH ] = 2 x 5 x 10 M
-2
-
[OH ] = 1 x 10 M
+
pOH = - log [H ]
-2
pOH = - log 10 M
pOH = 2
pH = 14 – 2 = 12

E-MODUL KIMIA ASAM BASA 57