Acids and Bases
Acids: vinegar, lemons, gastric juice
Bases: ammonia, baking soda, drano
Salts: table salt
Acids
Properties
Acids: 1. sour
2. change color of dyes
3. dissolve metals to form hydrogen
4. react with carbonates to form CO2
5. neutralize bases
water soluble acids form hydrogen ions
Bases
Properties
Bases: 1. bitter
2. change color of dyes
3. soapy feel
4. neutralize acids
In water, soluble bases can form
22OH or CO3 or O ions
These ions react with H+ ions
NH3 another common base
Acids/Base Theories
Sir Humphry Davy (1811)
All acids
contain
hydrogen
HCl
H2SO4
HNO3
Safety Lamp
Acids/Base Theories
Savante Arrhenius (1884)
Acid:
any substance
that produces
hydrogen ions
in water
Base:
any substance
that produces
hydroxide ions
in water
Acids/Base Theories
Savante Arrhenius (1884)
Acid:
any substance
that produces
hydrogen ions
in water
Base:
any substance
that produces
hydroxide ions
in water
HCl (aq)
6 H+ + Cl-
NaOH (aq)
6 Na+ + OH-
Definition limited to aqueous solutions
Acids/Base Theories
Bronsted -Lowry Definition (1923)
Acid:
proton donor
Base:
proton acceptor
Explains why ammonia is a base
Acids/Base Theories
Bronsted -Lowry Definition (1923)
Acid:
proton donor
NH3
Base:
proton acceptor
+
4
+ H2O 6 NH
+
-
OH
Strong Acids/Bases
Ionize completely
HCl
6
+
H
-
+ Cl
Strong Acids/Bases
Ionize completely
NaOH (aq) 6
Na+ (aq) +
OH- (aq)
Weak Acids/Bases
Incomplete ionization
+
2
HC2H3O2 º H + C2H3O
NH3
+
4
+ H2O º NH
+
-
OH
Note: water acts as an acid
Water can also act as a base
Autoionization of water
Water is amphiprotic
Can act either as acid or base
Weak Acids/Bases
Incomplete ionization
+
2
HC2H3O2 º H + C2H3O
+
HC2H3O2 + H2O º H3O + C2H3O2
+
H3O called hydronium ion
+
+
H 2O + H 6 H 3O
Conjugate Acids/Bases
Acids and bases that are
+
related by loss or gain of H
Common Acids/Bases
Acids
Bases
citrus fruits
aspirin
Coca Cola
vinegar
vitamin
baking soda
detergents
ammonia cleaners
Tums & Rolaids
soap
Common Acids/Bases
Acids
Formula
Molarity
nitric
hydrochloric
sulfuric
acetic
HNO3
HCl
H2SO4
HC2H3O2
16
12
18
18
Bases
Formula
Molarity
ammonia
sodium hydroxide
NH3
NaOH
18
solid
Common Acids
HCl
All are corrosive
cleans metals, brick, cement
H2SO4 car batteries, fertilizers,
industrial chemicals,
nitroglycerin
HNO3 fertilizers, dyes, plastics,
explosives
H2SO4
Assassination of President McKinley
Common Bases
NaOH
Ca(OH)
Ca(OH)2
drain cleaner,
soap manufacture
lime, mortar, plaster, cement
NH3
cleaner
Mg(OH)2 milk of magnesia
Drugs: cocaine, morphine, nicotine
Autoionization of water
Water is amphiprotic
+
-
H2O + H2O º H3O + OH
+
-
Kw = [H3O ][OH ]
-14
= 1.0 x 10
at 25E
EC
[H2O] is constant, included in Kw
Autoionization of water
+
-
H and OH always present
in aqueous solutions
Only for a neutral solution are
their concentrations equal
pH scale
+
-7
Neutral [H ] = 10 M
Acidic
Basic
-
= [OH ]
+
-7
-
+
-7
-
[H ] > 10 M > [OH ]
[H ] < 10 M < [OH ]
pH scale
Scale to measure acid and
base concentrations over
large concentration range
pH Scale
+
pH = - log [H ]
Logarithmic scale
+
+
[H ] = no. moles H per liter
of solution molarity
-
pOH = - log [OH ]
pH + pOH = 14
pH scale
scale: 0 - 14
Stronger acid
Stronger base
pH Scale
Measures
acidity
scale:
0 - 14
acid
base
pH calculations
Find pH of 0.015 M HCl
HCl
6
+
H
+
+
0.015 M HCI 60.015 M H
+
-
Cl
-
+ 0.015 M Cl
pH = - log[H ] = - log [0.015]
= 1.8
pH calculations
Find pH of 0.30 M Ca(OH)2
2+
Ca(OH)2
6 Ca
+
2 OH
6
0.3 M
+
-
2 x 0.3 M
= 0.6 M OH
-14
[H ][OH ] = 10
[H+] = 10-14 ÷ [OH- ] = 10-14 ÷ 0.6
-14
= 1.7 x 10 M
-14
pH = -log (1.7 x 10 ) = 13.8
pH calculations
+
Find [H ] for HCI solution
having pH = 9.0
+
9.0 = - log [H ]
+
find antilog
-9
[H ] = 1.0 x 10 M
-
+
-
-14
If [OH ] needed use [H ][OH ] = 10
Acid dissociation constant, K a
Ionization of weak acids is equilibrium
+
(aq)
HA (aq) + H2O (l) º H3O
+
Ka =
-
+ A
(aq)
−
[ H 3 O ][ A ]
[ HA]
Weak acid strength related to Ka
Note: water omitted from expression
Base dissociation constant, K b
Ionization of weak bases is equilibrium
+
B (aq) + H2O (l) º B
−
-
+ OH (aq)
(aq)
+
[OH ][ BH ]
Kb =
[ B]
Weak base strength related to Kb
Note: water omitted from expression
Ka and Kb values
Always < 1
Size of Ka indicates acid strength
Size of Kb indicates base strength
Most acids and bases are weak
For a conjugate acid-base pair:
-14
Ka x Kb = 10
Polyprotic acids
4
+
H2SO4 º H + HSO
HSO
4
HSO
+
24
º H + SO
SO
More difficult to remove
+
each subsequent H
pH of weak acid solutions
Find the pH of a 0.05 M acetic
acid solution
-5
Ka for HC2H3O2 = 1.8 x 10
+
2
HC2H3O2 º H + C2H3O
pH of weak acid solutions
Find the pH of a 0.05 M acetic
acid solution
-5
Ka for HC2H3O2 = 1.8 x 10
+
2
HC2H3O2 º H + C2H3O
+
Ka =
−
[ H ]eq [C2 H 3 O2 ]eq
[ HC2 H 3 O2 ]eq
pH of weak acid solutions
2
+
HC2H3O2 º H + C2H3O
[initial]
Change
[equ]
0.050 M
-x
0.050-x
0
+x
x
Solve for x
0
+x
x
pH of weak acid solutions
x× x
−5
= 18
. × 10
0.050 − x
pH of weak acid solutions
x× x
−5
= 18
. × 10
0.050 − x
Use quadratic equation to solve x
-4
X = 9.24 x 10
=
+
[H ]eq
-4
pH = - log(9.24 x 10 )
= 3.03
Salts
Product of acid + base reaction
HCl + NaOH 6 NaCl + H2O
when an acid reacts with a
base a salt and water form
when the base is a carbonate
also form CO2 gas
Some Reactions
Mg + 2 HCl 6 MgCl2 + H2
HCl + NaOH 6 NaCl + H2O
Both are neutralization reactions
2 HCl + Na2CO3 6 2 NaCl + CO2 + H2O
Titrations
Methods based on volume
Need: buret, pipet, balance,
balance, indicator
2 HCl + Na2CO3 6 2 NaCl + CO2 + H2O
2 moles acid = 1 mole base
2 MAVA = 1 MB VB
2 MAVA = 1 massB
form. Wt.B
Indicators
Weak organic acids
+
H-Indic » Indic + H
color 1
color 2
Change color at end-point
Coincides with equivalence point
pH of ions
+
4
3+
Acid: NH
4
Al
HSO
-
-
Base: CH3 COO
2-
CN S
3+
Fe
-
2-
F O
23
CO
Neutral: group 1,2 metal ions
4
ClO
-
Cl
-
-
23
Br I NO
24
SO
pH of ions
Predict the following:
ammonium chloride
calcium nitrate
lithium sulfide
ammonium acetate
pH of ions
Find the pH of a 0.10 M KCH3COO solution
Write ionization equation
+
KCH3COO 6 K
+
CH3COO
CH3COO - +
H2O 6 CH3COOH
Find [OH -]
6 [H
[H+] 6 pH
-
+
OH -
Neutralization
Strong acid + strong base 6 neutral
Strong acid + weak base 6 weak acid
Weak acid + strong base 6 weak base
Weak acid + weak base 6 ?
Lewis acid-base theory
Acids: acept pair of electrons
+
+
Positive ions: H Ag BF3
Bases: donate pair of electrons
Negative ions: F OH NH3