1. Acids & Bases
SCH3u/4C
Ms. Richardson

2. Acids & Bases
Acids and bases were originally defined by their properties:
Acids
Bases
Liquid or solid
Corrosive
Sour taste
Conducts electricity
Reacts with most metals to produce H2 gas
Reacts with carbonates to produce CO2
Liquid or base
Bitter taste
Reacts with acids
Doesn’t react with metal
Soapy/slippery feeling

3. The Arrhenius Theory
Scientists began to realize that defining acids and bases based on their chemical behavior was more accurate.
Svante Arrhenius ( ) defined acids as substances that produce hydrogen ions (H+) in solution.
HCl(aq)  H+(aq) + Cl-(aq)
H2SO4(aq)  2H+(aq) + SO42-(aq)
He defined bases as substances that produce hydroxide ions (OH-) in solution.
NaOH(aq)  Na+(aq) + OH-(aq)
Ca(OH)2 (aq)  Ca2+(aq) + 2OH-(aq)

4. Acid Base Indicators
Acid-base indicators are chemicals that can be used to identify acids and bases by detecting the presence of H+ ions.
Indicators
Acid Colour
Base Colour
Blue Litmus Paper
Red
Blue
Red Litmus Paper
Bromothyl Blue
Yellow
Phenolphthalein
Colourless
Pink
Methyl Orange

5. Limitations to the Arrhenius Theory
The hydrogen ion is extremely reactive.
As soon as the acid dissociates in water, H+ reacts with the water to form the hydronium ion (H3O+).
H+ + H2O  H3O+
Hydrogen and hydronium ions are often used interchangeably as their chemical behavior is the same

6. Limitations to the Arrhenius Theory
The dissociation of the base ammonia (NH3) does not result in the production of hydroxide ions.
We can show the hydroxide ion produced by showing the reaction with water:
NH3 + HOH  NH4+ + OH-

7. Strong Acids and Strong Bases
Acids and bases that dissociate completely are considered to be strong acids/bases.
Examples: H2SO4, HCl
HCl + H2O  H3O+ + Cl-
1.0 mol/L mol/L
When an acid or base only partially dissociates, it is referred to as a weak acid/base.
Example: Acetic acid dissociates at 5%
CH3COOH + H2O  H3O+ + CH3COO-
1.0 mol/L mol/L