Chapter 16 Acid-Base and Solubility Equilibria

The shift in equilibrium caused by the addition of a compound having an ion in common with the dissolved substance

The common ion effect as it relates to pH:
We derive Ka from the simplified equation of a weak acid and soluble salt in solution

HA (aq) → H+ (aq) + A-(aq)


← Equilibrium constant expression

← Hydrogen ion concentration

← Negative log of concentration

← Henderson-Hasselbalch equation


Buffer Solutions

A buffer solution is a solution of a weak acid or weak base and the salt of the weak acid/base that has the ability to resist change in pH.

Buffer solutions must contain a relatively large concentration of acid to react with any OH- ions that are added to it and a similar concentration of base to react with any added H+ ions.

sodium acetate dissociates completely in water

hydrogen ions are consumed by the conjugate base

OH ions are neutralized by the acid in the buffer

The two reactions that characterize this buffer system are identical to those for the common ion effect

Buffer system written as:

Buffering Capacity

  • The effectiveness of the buffer solution
  • Depends on the amount of acid and conjugate base from which the buffer is made

Acid-Base Titrations

Strong Acid-Strong Base Titrations
When the strong base is added to the strong acid, the pH of the solution increases slowly at first. Near the equivalence point, the pH begins to rise steeply, and at the equivalence point, the curve rises almost vertically. The addition of a single drop of the base can cause a large increase in hydroxide ion concentration and a large increase in the pH of the solution.


Weak Acid-Strong Base Titrations


The pH at the equivalence point is greater than 7 as a result of the excess hydroxide ions formed.

Strong Acid-Weak Base Titrations