Question

The pKa of a certain weak acid is 5.0. Calculate the ratio of proton acceptor to proton donor at pH 7.0.
A) 1000:1
B) 20:1
C) 100:1
D) 40:1

Answer 1

Answer:

C) 100:1

Explanation:

To solve this question we must use H-H equation:

pH = pKa + log [A-] / [HA]

Where pH = 7.0, pKa = 5.0, A- is proton aceptor and HA proton donor.

Replacing:

7 = 5 + log [A-] / [HA]

2 = log [A-] / [HA]

100 = [A-] / [HA]

That means the ratio of proton aceptor:proton donor is:

C) 100:1