Finding The pH Of A Weak Acid

Question 1

What is the Ka equation for a weak acid?

Answer 1

Ka = [H+][A-] / [HA]

Question 2

How do you calculate Ka from pKa (and vice versa)?

Answer 2

pKa = - log (Ka)
Ka = log ^-pKa

Question 3

What are the two approximations for calculating pH of a weak acid solution from Ka?

Answer 3

1. [H+] = [A-]
2. [HA] (at eq.) = [A-] (at eq.)