Titration Graphs

1
Titration Graphs
2
Strong Acid - Strong Base

• Investigating the titration between

1M HCl and 1M NaOH
3
Strong Acid - Strong Base
HCl
10 ml NaOH
4
Strong Acid - Strong Base
HCl
10 ml NaOH
5
Strong Acid - Strong Base
HCl
10 ml NaOH
6
Strong Acid - Strong Base
HCl
10 ml NaOH
7
Strong Acid - Strong Base
NaOH HCl NaCl H2O
1NaOH 1HCl NaCl H2O
1M 1M
10ml
10ml
Solutions mixed in the right proportions
according to the equation.
8
Strong Acid - Strong Base
Running acid into alkali
Running alkali into acid
9
Strong Acid - Weak Base

• Investigating the titration between

1M HCl and 1M NH3(aq)
10
Strong Acid - Weak Base
1NH3 1HCl NH4Cl
1M 1M
25ml
25ml
pH falls less quickly as buffer soln formed
(excess NH3 and NH4Cl present)
Soln at equivalence point is slightly acidic
because ammonium ion is slightly acidic
NH4 H2O ? NH3 H3O
11
Strong Acid - Weak Base
After equivalence point the soln contains NH3 and
NH4Cl a buffer soln and so resists large
increse in pH so graph flattens out.
alkali
acid
12
Strong Acid - Weak Base
Running acid into alkali
Running alkali into acid
13
Weak Acid - Strong Base

• Investigating the titration between

1M CH3COOH and 1M NaOH
14
Weak Acid - Strong Base
1CH3COOH 1NaOH CH3COONa
1M 1M
25ml
25ml
Soln at equivalence point is slightly alkaline
because ethanoate ion is slightly alkaline
pH falls less quickly as buffer soln formed
(excess CH3COOH and CH3COO- present)
CH3COO- H2O ? CH3COOH OH-
15
Weak Acid - Strong Base
Excess of alkali present graph same as when
adding strong alkali to strong acid
pH rises less quickly as buffer soln formed
(excess CH3COOH and CH3COO- present)
16
Weak Acid - Strong Base
Running acid into alkali
Running alkali into acid
17
Weak Acid - Weak Base

• Investigating the titration between

1M CH3COOH and 1M NH3
18
Weak Acid - Weak Base
1CH3COOH 1NH3 CH3COO- 1NH4
About as weak as each other -
19
Weak Acid - Weak Base
No steep section small addition of acid causes
a large change in pH, so
Very difficult to do a titration between a weak
acid and a weak base.
20
Weak Acid - Weak Base
21
Complicated titration curves
Hydrochloric acid and sodium carbonate
Strong Acid - Weak Base
hydrochloric acid
Na2CO3 HCl ? NaCl CO2 H2O
2
1
2
Assume both solutions are of the same
concentration
Reacting ratio is 12
Twice the volume of hydrochloric acid required to
reach the equivalence point
Sodium carbonate
22
Complicated titration curves
Na2CO3 2HCl ? 2NaCl CO2 H2O
weak base, CO32-
hydrochloric acid
Twice the volume of hydrochloric acid required to
reach the equivalence point
50cm3
Sodium carbonate
50
25cm3
23
Complicated titration curves
Na2CO3 2HCl ? 2NaCl CO2 H2O
hydrochloric acid
Twice the volume of hydrochloric acid required to
reach the equivalence point
50cm3
Sodium carbonate
25cm3
24
Complicated titration curves
Na2CO3 2HCl ? 2NaCl CO2 H2O
NO CO2 observed whilst adding first 25 ml of acid
hydrochloric acid
A
CO2 observed whilst adding next 25 ml of acid
Twice the volume of hydrochloric acid required to
reach the equivalence point
B
50cm3
excess acid
Sodium carbonate
25
50
25cm3
25
Complicated titration curves
Na2CO3 2HCl ? 2NaCl CO2 H2O
Na2CO3 HCl ? NaCl NaHCO3
A
NaHCO3 HCl ? NaCl CO2 H2O
B
26
Complicated titration curves
Na2CO3 2HCl ? 2NaCl CO2 H2O
Na2CO3 HCl ? NaCl NaHCO3
NaHCO3 HCl ? NaCl CO2 H2O
Na2CO3 2HCl ? 2NaCl CO2 H2O
A
B
27
Complicated titration curves
Ethanedioic acid and sodium hydroxide
Weak Acid - Strong Base
Sodium hydroxide
Assume both solutions are of the same
concentration
Reacting ratio is 12
(COOH)2 NaOH ? (COONa)2 H2O
2
1
Twice the volume of sodium hydroxide required to
reach the equivalence point.
Two hydrogen ions can be formed per molecule of
the acid. It is a
ethanedioic acid
DIPROTIC ACID
28
Complicated titration curves
(COOH)2 NaOH ? (COONa)2 H2O
2
1
sodium hydroxide
Twice the volume of sodium hydroxide required to
reach the equivalence point
50cm3
fairly strong acid
ethanedioic acid
50
25cm3
29
Complicated titration curves
(COOH)2 2NaOH ? (COONa)2 H2O
reaction is in TWO stages
one of the hydrogens is easier to remove than the
other
30
Choosing an Indicator
3.7
9.3
31
Strong Acid - Strong Base
32
Strong Acid - Weak Base
33
Weak Acid - Strong Base
34
Weak Acid Weak Base
35
Acid - Carbonate