Acids and Bases

1
Acids and Bases
2
General properties

• ACIDS
• Taste sour
• Turn litmus
• React with active metals Fe, Zn
• React with bases

• BASES
• Taste bitter
• Turn litmus
• Feel soapy or slippery (react with fats to make
  soap)
• React with acids

3
Definitions

• Acids produce H
• Bases - produce OH-
• Acids donate H
• Bases accept H
• Acids accept e- pair
• Bases donate e- pair

Arrehenius
only in water
Bronsted-Lowry
any solvent
Lewis
used in organic chemistry, wider range of
substances
4
Examples
Arrhenius
NaOH
HCl
Bronsted-Lowry
NH3
HCl
NH3
BF3
Lewis
The hydrogen ion in aqueous solution
H H2O ? H3O (hydronium ion)
5
The Bronsted-Lowry Concept
Conjugate pairs
CH3COOH CH3COO-
HCl Cl-
NH4 NH3
HNO3 NO3-
How does a conjugate pair differ?
H transfer
6
Neutralization
In general Acid Base ? Salt Water
double displacement reactions.
HCl NaOH ? NaCl HO H
HCl Mg(OH)2 ?
H2SO4 NaHCO3 ?
7
Concentration and Strength

• Concentration
• Molarity (M)
• Moles of solute per liter of solution
• Strength
• Degree of dissociation
• How much the ions split when it dissolves

8
Lets examine the behavior of an acid, HA, in
aqueous solution.
HA
What happens to the HA molecules in solution?
9
100 dissociation of HA
HA
H
Strong Acid
A-
Would the solution be conductive?
10
Partial dissociation of HA
HA
H
Weak Acid
A-
Would the solution be conductive?
11
HA ? H A-
HA
H
Weak Acid
A-
At any one time, only a fraction of the molecules
are dissociated.
12
Strong and Weak Acids/Bases
Strong acids/bases 100 dissociation into
ions HCl NaOH HNO3 KOH H2SO4
Weak acids/bases partial dissociation,
both ions and molecules CH3COOH NH3
13
acid rain (NOx, SOx) pH of 4.2 - 4.4 in
Washington DC area
pH
0-14 scale for the chemists
2
3
4
5
6
7
8
9
10
11
12
neutral _at_ 25oC (H) (OH-) distilled water
acidic (H) gt (OH-)
basic or alkaline (H) lt (OH-)
natural waters pH 6.5 - 8.5
normal rain (CO2) pH 5.3 5.7
fish populations drop off pH lt 6 and to zero pH lt
5
14
pH

• Measures H concentration
• pH of 1 1 x 10-1 M H
• pH of 7 1 x 10-7 M H
• pH of 14 1 x 10-14 M H

15
pH indicators

• Change color based on pH of the solution
• Litmus Paper
• Phenolphthalein
• pH range 1-8.2 colorless
• pH range 8.3-10 pink color

16
When life goes either way amphoteric
(amphiprotic) substances
Acting like a base
Acting like an acid
HCO3-
H2CO3
CO3-2
accepts H
donates H
17
Show how water can be amphoteric.
H2O