Titration Graphs. KeMsoft062 Strong Acid - Strong Base Investigating the titration between: 1M HCl...

Titration Graphs

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Strong Acid - Strong Base

Investigating the titration between:

1M HCl and 1M NaOH

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HCl

10 ml NaOH

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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

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HCl

10 ml NaOH


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


pH

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HCl

10 ml NaOH


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


pH

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0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

0 5 10 15 20 25


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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Running acid into alkali Running alkali into acid

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Strong Acid - Weak Base


1M HCl and 1M NH3(aq)

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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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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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Weak Acid - Strong Base


1M CH3COOH and 1M NaOH

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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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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 - Weak Base


1M CH3COOH and 1M NH3

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acid

alkali

1CH3COOH + 1NH3 = CH3COO- + 1NH4+

About as weak as each other -

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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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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


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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


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hydrochloric acid

Sodium carbonate


25cm3

50cm3

Twice the volume of


point


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hydrochloric acid

Sodium carbonate


25cm3

50cm3

Twice the volume of


point


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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A

B

Na2CO3 + HCl NaCl + NaHCO3

NaHCO3 + HCl NaCl + CO2 + H2O

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A

B

Na2CO3 + HCl NaCl + NaHCO3

NaHCO3 + HCl NaCl + CO2 + H2O


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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


Two hydrogen ions can be formed per molecule of the acid. It is a… DIPROTIC ACID

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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)


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

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Choosing an Indicator3.7 9.3

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Weak Acid – Weak Base

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Acid - Carbonate

Titration Graphs. KeMsoft062 Strong Acid - Strong Base Investigating the titration between: 1M HCl...

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Transcript of Titration Graphs. KeMsoft062 Strong Acid - Strong Base Investigating the titration between: 1M HCl...