Titration Graphs

KeMsoft06 2

Strong Acid - Strong Base

Investigating the titration between:

1M HCl and 1M NaOH

KeMsoft06 3

Strong Acid - Strong Base

HCl

10 ml NaOH

KeMsoft06 4

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.

KeMsoft06 8

Strong Acid - Strong Base

Running acid into alkali Running alkali into acid

KeMsoft06 9

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

KeMsoft06 11

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.

KeMsoft06 12

Strong Acid - Weak Base

Running acid into alkali Running alkali into acid

KeMsoft06 13

Weak Acid - Strong Base

Investigating the titration between:

1M CH3COOH and 1M NaOH

KeMsoft06 14

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

KeMsoft06 15

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

KeMsoft06 16

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 -

KeMsoft06 19

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.

KeMsoft06 20

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

KeMsoft06 24

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

KeMsoft06 25

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

KeMsoft06 27

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

KeMsoft06 29

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

KeMsoft06 31

Strong Acid - Strong Base

KeMsoft06 32

Strong Acid - Weak Base

KeMsoft06 33

Weak Acid - Strong Base

KeMsoft06 34

Weak Acid – Weak Base

KeMsoft06 35

Acid - Carbonate