Properties of Acids







Taste sour
pH < 7
Turn litmus red
Colorless with phenolphthalein
Neutralize bases
React with metals to produce H2 gas
React with carbonates to produce CO2, H2O,
and a salt.
Properties of Bases







Taste bitter
pH > 7
Turn litmus blue
Bright pink with phenolphthalein
Neutralize acids
Dissolve wool
Feel slippery
Acid Base Definitions

Originally recognized by properties like taste,
feel, reactions with indicators
Arrenhius Definition



Acids produce excess Hydrogen ions when
added to water
Bases produce excess Hydroxide ions when
added to water
Issues:
–
–
Very limited definition
Very few substances can actually be classified by
this definition.
Bronsted-Lowry Definition

Acids are proton victims, “donors”
–

Bases are proton thieves, “acceptors”
–

The molecule loses an H+
Steal an H+ from another molecule
More frequently used
Conjugate base


Ion that is formed when an acid donates a
Hydrogen ion (proton)
Examples:
Acid
Conjugate base
H2SO4
HSO41HNO3
NO31HC2H3O2 C2H3O21-
Conjugate base

If original acid is a strong acid, the conjugate
base is so weak that is does not behave as a
base.
–


It behaves as a neutral species
If original acid is a weak acid, the conjugate
base behaves as a weak base
(Important for equilibrium considerations later)
Conjugate acid


Ion that is formed when a base accepts a
Hydrogen ion
Examples:
Base
Conjugate acid
NaOH
H2O
NH3
NH41+
Conjugate acid

If original base is a strong base, the conjugate
acid is so weak that is does not behave as an
acid.
–

It behaves as a neutral species
If original base is a weak base, the conjugate
acid behaves as a weak acid
Amphoteric Substances

A species that can behave as either an acid or
a base

Water is the best example of an amphoteric
substance
Strong Acids



Acid that dissociates completely in water
100% of the sample breaks apart into ions
Six strong acids:
1.
2.
3.
4.
5.
6.
*
HCl
HBr
HI
HNO3
H2SO4
HClO4
HClO3
-
Hydrochloric acid
Hydrobromic acid
Hydroiodic acid
Nitric acid
Sulfuric acid
Perchloric acid
Chloric acid is borderline
Strong Base



Base that dissociates completely in water
100% of the sample breaks apart into ions
Strong bases
–
Hydroxides of the metals in group 1A and 2A
(not Be or Mg)
Weak acid or weak base




Do NOT dissociate completely in water
In water, establishes equilibrium between the
molecular form and ionic form
Any acid or base that is not a strong acid or
base is weak
Example:
Acetic acid
HC2H3O2 + H2O  C2H3O21- + H3O1+
Autoionization of water

The transfer of a hydrogen ion from one water
molecule to another water molecule,
–


results in the formation of a hydroxide ion and a
hydronium ion.
Equation:
2 H2O  H3O1+ + OH1Equal amounts of hydroxide and hydronium
are formed,
–
so water remains neutral.
pH system

The pH of a system is an indication of the
[H3O1+]. While it is based on the
autoionization of water, it works for all acidbase systems.
pH system




Definitions:
pH = -log [H3O1+]
pOH = -log [OH1-]
pKw = -log Kw
Since Kw = 1.0 x 10-14, pKw = -log (1.0 x 10-14) = 14

Kw = [H3O1+] [OH-1] 
pKw = pH + pOH = 14
pH Strong Acids and Bases

[H3O1+] = initial concentration of acid
–
To find the pH of a strong acid, use the initial
concentration of the acid as the concentration of
H3O1+

[OH1-] = initial concentration of base

pH (strong acid) = -log (initial conc.)