WEAK ACIDS and WEAK BASES are weak electrolytes that do not completely ionize in solution, but instead form an equilibrium. 

Weak Acid-Base Equilibria

Example #1: What is the original molarity of a solution of weak acid with a Ka of 4.7 x 10-3 and pH of 4.12 at 25 oC?

Example #2: You are seeking to identify an unknown monoprotic acid by determining its Ka value. A 6.05 x 10-2 M solution of this unknown monoprotic acid has a pH of 2.122. Determine the Ka of this unknown acid?

a) 4.47 x 10-4
b) 9.42 x 10-4
c) 2.85 x 10-2
d) 1.08 x 10-3
e) 3.58 x 10-1

Example #3: A weak acid has a pKa of 5.35. What is the hydronium ion concentration in a 0.10 M solution of this weak acid?

a) 5.4 x 10-4 M

b) 6.3 x 10-6 M

c) 3.5 x 10-5 M

d) 2.3 x 10-6 M

e) 4.5 x 10-6 M

f) 6.7 x 10-4 M

Practice: The pH of an aqueous 0.10 M nitrite ion is 8.17. What is the base dissociation constant of the base?