## Section 6: Misc Facts About Acids-Bases

#### Equilibrium Expression

The equilibrium expression is exactly the same thing as the equilibrium constant earlier in this unit, except it is called the acid dissociation constant and has the variable (Ka when it is for an acid and Kb when it is for a base.)

So for the reaction:

HA (aq) + H2OL <=====> H3O+(aq) + A-(aq)

the acid dissociation constant is:

Ka = [H3O+] [A-] / [HA] Ka = [H +] [A-] / [HA]

(Note1: Liquids don't get put into the expression) Note 2: H3O+ is the same thing as H+

#### Strength of Acids

It is important to know the next few facts. First, acids are strong when they dissociate a lot in water (most of the acid breaks up.) Secondly, acids are weak when then don't dissociate in water (only small amounts of the acid actually break up.) Third, the stronger the acid the weaker the conjugate base. Fourth, the weaker the conjugate acid the stronger the conjugate base.

#### Monoprotic, Diprotic, Triprotic

A monprotic acid is an acid that only gives up one H+ ion. For instance, HCl is a monoprotic acid. A diprotic acid is an acid that gives off the H+ ions. For example, H2SO4 breaks up, first into H+ and HSO4 then breaks up into H+ and SO4-2. (Note: It takes two steps to break up H2SO4.) A triprotic acid is an acid that gives up 3 H+ ions. For example, H3PO4, first breaks up into H+ and H2PO4- then breaks up into H+ an HPO4-2 the breaks up into H+ and PO4-3. (Note: It takes three steps to break up H3PO4.)