The dissociation constant of weak acid is 1 10-4. In order to prepare a buffer solution with a pH = 5, the [Salt]/[Acid] ratio should be
- 4 : 5
- 10 : 1
- 5 : 4
- 1 : 10
Answer
(2) 10 : 1
Solution
pKa = - (1 10-4) = 4
Henderson–Hasselbalch equation: pH = pKa + [Salt][Acid]
⇒ 5 = 4 + [Salt][Acid]
⇒ [Salt][Acid] = 10
∴ Ratio = 10 : 1
Answer: (2)