1. Weak Acids Ch 16
Video

2. Weak Acids Equilibrium lies far to the left (or reactant side)
They HARDLY dissociate!
Ex. HC2H3O2
Small Ka = weak acid
The weaker the acid, the stronger the conjugate base.

3. Dissociation of Weak Acids
Weak acids are assumed to dissociate only slightly (less than 5%) in solution.
Large Ka or small Ka?
Reactant favored or product favored?

4. Dissociation Constants: Weak Acids
Formula
Conjugate Base Ka
 Iodic 
 HIO3 
 IO3- 
 1.7 x 10-1 
 Oxalic 
 H2C2O4 
 HC2O4- 
 5.9 x 10-2 
 Sulfurous 
 H2SO3 
 HSO3- 
 1.5 x 10-2 
 Phosphoric 
 H3PO4 
 H2PO4- 
 7.5 x 10-3 
 Citric 
 H3C6H5O7 
 H2C6H5O7- 
 7.1 x 10-4 
 Nitrous 
 HNO2 
 NO2- 
 4.6 x 10-4 
 Hydrofluoric 
HF 
 F- 
 3.5 x 10-4 
 Formic 
 HCOOH 
 HCOO- 
 1.8 x 10-4 
 Benzoic 
 C6H5COOH 
 C6H5COO- 
 6.5 x 10-5 
 Acetic 
 CH3COOH 
 CH3COO- 
 1.8 x 10-5 
 Carbonic 
 H2CO3 
 HCO3- 
 4.3 x 10-7 
 Hypochlorous 
 HClO 
 ClO- 
 3.0 x 10-8 
 Hydrocyanic 
 HCN 
 CN- 
 4.9 x 10-10 
Reactant favored!

5. Diprotic acids
An acid that has 2 acidic protons
Ex. sulfuric acid

6. In a strong diprotic acid- large Ka for 1st proton
Small Ka for 2nd proton

7. Polyprotic
More than one proton dissociates
Ex. H2SO4
Ex. H3PO4

8. Practice
Use data below to rank the following acids from weakest to strongest
Name of acid
Ka value
Hydrogen sulfate ion
1.2 x 10-2
Acetic acid
1.8 x 10-8
Phenol
1.6 x 10-10
Hydrofluoric acid
7.2 x 10-4

9. Water H20(l) +H20(l) H30+(aq) +OH- (aq) In neutral solution:
Amphoteric: can behave as either an acid or a base
Autoionization of water:
H20(l) +H20(l) H30+(aq) +OH- (aq)
In pure water: [H+]=[OH-] =1.00 x 10-7
Kw = equilibrium of autoionization of water
So Kw=
In neutral solution:
In an acidic solution:
In a basic solution:

10. Example
Calculate [H+] in the following solution and state whether the solution is neutral, acidic, or basic.
1.0 x 10-6 M OH-