Post on 28-Jan-2016
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Titration Graphs
KeMsoft06 2
Strong Acid - Strong Base
Investigating the titration between:
1M HCl and 1M NaOH
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Strong Acid - Strong Base
HCl
10 ml NaOH
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Strong Acid - Strong Base
HCl
10 ml NaOH
pH During a Titration
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 2 4 6 8 10 12 14 16 18 20
Volume of acid added / ml
pH
KeMsoft06 5
Strong Acid - Strong Base
HCl
10 ml NaOH
pH During a Titration
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 2 4 6 8 10 12 14 16 18 20
Volume of acid added / ml
pH
KeMsoft06 6
Strong Acid - Strong Base
HCl
10 ml NaOH
pH During a Titration
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 2 4 6 8 10 12 14 16 18 20
Volume of acid added / ml
pH
KeMsoft06 7
Strong Acid - Strong Base
pH During a Titration
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 5 10 15 20 25
Volume of acid added / ml
pH
Equivalence point at pH7
NaOH + HCl = NaCl + H2O 1M 1M
1NaOH + 1HCl = NaCl + H2O
10ml 10ml
Solutions mixed in the right proportions according to the equation.
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Strong Acid - Strong Base
Running acid into alkali Running alkali into acid
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Strong Acid - Weak Base
Investigating the titration between:
1M HCl and 1M NH3(aq)
KeMsoft06 10
Strong Acid - Weak Base
1M 1M1NH3 + 1HCl = NH4Cl
25ml 25mlpH starts to fall quickly as acid is added
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+
Weak base so initial pH value is less than 14
acid
alkali
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Strong Acid - Weak Base
alkali
acid
Excess of acid present – graph same as when adding strong acid to strong alkali
After equivalence point the soln contains NH3 and NH4Cl – a buffer soln and so resists large increse in pH so graph flattens out.
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Strong Acid - Weak Base
Running acid into alkali Running alkali into acid
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Weak Acid - Strong Base
Investigating the titration between:
1M CH3COOH and 1M NaOH
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Weak Acid - Strong Base
1M 1M1CH3COOH + 1NaOH = CH3COONa
25ml 25ml
pH falls less quickly as buffer soln formed (excess CH3COOH and CH3COO- present)
Soln at equivalence point is slightly alkaline because ethanoate ion is slightly alkaline
CH3COO-+ H2O CH3COOH + OH-
acid
alkali
Excess of alkali present – graph same as when adding strong acid to strong alkali
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Weak Acid - Strong Base
alkali
acid
pH starts to rise quickly as alkali is added
pH rises less quickly as buffer soln formed (excess CH3COOH and CH3COO- present)
Excess of alkali present – graph same as when adding strong alkali to strong acid
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Weak Acid - Strong Base
Running acid into alkali Running alkali into acid
KeMsoft06 17
Weak Acid - Weak Base
Investigating the titration between:
1M CH3COOH and 1M NH3
KeMsoft06 18
Weak Acid - Weak Base
acid
alkali
1CH3COOH + 1NH3 = CH3COO- + 1NH4+
About as weak as each other -
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Weak Acid - Weak Base
acid
alkali
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.
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Weak Acid - Weak Base
KeMsoft06 21
Complicated titration curves
hydrochloric acid
Sodium carbonate
Na2CO3 + HCl NaCl + CO2 + H2O
Assume both solutions are of the same concentration
21
2
Reacting ratio is 1:2
Twice the volume of hydrochloric acid required to reach the equivalence point
Hydrochloric acid and sodium carbonate
Strong Acid - Weak Base
KeMsoft06 22
5050
hydrochloric acid
Sodium carbonate
Na2CO3 + 2HCl 2NaCl + CO2 + H2O
25cm3
50cm3
50
weak base, CO32-
Twice the volume of
hydrochloric acid required to reach the equivalence
point
Complicated titration curves
KeMsoft06 23
hydrochloric acid
Sodium carbonate
Na2CO3 + 2HCl 2NaCl + CO2 + H2O
25cm3
50cm3
Twice the volume of
hydrochloric acid required to reach the equivalence
point
Complicated titration curves
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hydrochloric acid
Sodium carbonate
Na2CO3 + 2HCl 2NaCl + CO2 + H2O
25cm3
50cm3
Twice the volume of
hydrochloric acid required to reach the equivalence
point
Complicated titration curves
A
B
NO CO2 observed whilst adding first 25 ml of acid
CO2 observed whilst adding next 25 ml of acid
25 50
excess acid
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Na2CO3 + 2HCl 2NaCl + CO2 + H2O
Complicated titration curves
A
B
Na2CO3 + HCl NaCl + NaHCO3
NaHCO3 + HCl NaCl + CO2 + H2O
KeMsoft06 26
Na2CO3 + 2HCl 2NaCl + CO2 + H2O
Complicated titration curves
A
B
Na2CO3 + HCl NaCl + NaHCO3
NaHCO3 + HCl NaCl + CO2 + H2O
Na2CO3 + 2HCl 2NaCl + CO2 + H2O
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Complicated titration curves
Sodium hydroxide
ethanedioic acid
(COOH)2 + NaOH (COONa)2 + H2O
Assume both solutions are of the same concentration
21
Reacting ratio is 1:2
Twice the volume of sodium hydroxide required to reach the equivalence point.
Ethanedioic acid and sodium hydroxide
Weak Acid - Strong Base
Two hydrogen ions can be formed per molecule of the acid. It is a… DIPROTIC ACID
KeMsoft06 28
50
sodium hydroxide
ethanedioic acid
25cm3
50cm3
50
fairly strong acid
Twice the volume of
sodium hydroxide required to reach the
equivalence point
Complicated titration curves (COOH)2 + NaOH (COONa)2 + H2O21
50
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Volume of alkali added (cm3)
Complicated titration curves
sodium hydroxide
ethanedioic acid
25cm3
50cm3
Twice the volume of
sodium hydroxide required to reach the
equivalence point
(COOH)2 + 2NaOH (COONa)2 + H2O
reaction is in TWO stages
one of the hydrogens is
easier to remove than
the other
KeMsoft06 30
Choosing an Indicator3.7 9.3
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Strong Acid - Strong Base
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Strong Acid - Weak Base
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Weak Acid - Strong Base
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Weak Acid – Weak Base
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Acid - Carbonate