Shapes of Titration Curves

Concepts and Exercises

Rafa Muñoa

Lizardi Institutua

Zarautz

Different shapes of curves and their meanings

Shapes of curves

Titration curves can be considered as combinations of 1-2-3-4 half-curves with 5-6-7-8 half curves.

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1-2-3-4 half-curves represent states before equivalence points and, thus, give information about the system to be neutralized (erlenmeyer flask).

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5-6-7-8 half-curves represent states after equivalence points and, thus, give information about the solution that titrates (buret).

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Rafa Muñoa

Lizardi Institutua

Zarautz

Different shapes of curves and their meanings

Case #1

ERLENMEYER FLASK: Initially the pH is close to 14, which indicates that we have a strong base to be titrated.

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BURET: After equivalence point, the pH decreases until it reaches a pH close to 0-1, which tells us that the solution in the buret is a strong acid.

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EQUIVALENCE POINT: At equivalence point, there is only a salt that comes from a strong acid and a strong base and undergo no hydrolysis. Thus, pH=7.

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8

equivalence point: pH=7

Rafa Muñoa

Lizardi Institutua

Zarautz

Different shapes of curves and their meanings

Case #2

ERLENMEYER FLASK: Initially the pH is basic but not close to 14, which indicates that we have a weak base to be titrated.

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BURET: After equivalence point, the pH decreases until it reaches a pH that is not close to 0-1, which tells us that the solution in the buret is a weak acid.

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EQUIVALENCE POINT: At equivalence point, the pH will be close to 7.

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5

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7

1

8

equivalence point: pH=7

2

Rafa Muñoa

Lizardi Institutua

Zarautz

Different shapes of curves and their meanings

Case #3

ERLENMEYER FLASK: Initially the pH is acid and pH is close to 0-1, which indicates that we have a strong acid to be titrated.

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BURET: After equivalence point, the pH increases and it reaches a pH that is not close to 14, which tells us that the solution in the buret is a weak base.

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EQUIVALENCE POINT: At equivalence point, the pH will be lower than 7 because the cation from the salt will undergo a hydrolysis process (H₃O⁺).

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5

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7

1

8

equivalence point: pH<7

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4

Rafa Muñoa

Lizardi Institutua

Zarautz

Different shapes of curves and their meanings

Case #4

ERLENMEYER FLASK: Initially the pH is acid and pH is not close to 0-1, which indicates that we have a weak acid to be titrated.

​

BURET: After equivalence point, the pH increases and it reaches a pH that is close to 14, which tells us that the solution in the buret is a strong base.

​

EQUIVALENCE POINT: At equivalence point, the pH will be higher than 7 because the anion from the salt will undergo a hydrolysis process (OH^-).

5

6

7

1

8

equivalence point: pH>7

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4

3

Rafa Muñoa

Lizardi Institutua

Zarautz

Exercise #1:

Titration of HCl with NaOH

In this titration:

• Draw the corresponding curve
• Indicate and justify the equivalence point
• Suggest the property ideal indicator should have

Rafa Muñoa

Lizardi Institutua

Zarautz

Exercise #2:

Titration of acetic acid with NaOH

In this titration:

• Draw the corresponding curve
• Indicate and justify the equivalence point
• Suggest the property ideal indicator should have

Rafa Muñoa

Lizardi Institutua

Zarautz

Exercise #3:

Titration of ammonia with HCl

In this titration:

• Draw the corresponding curve
• Indicate and justify the equivalence point
• Suggest the property ideal indicator should have

Rafa Muñoa

Lizardi Institutua

Zarautz

Rafa Muñoa

Lizardi Institutua

Zarautz

Rafa Muñoa

Lizardi Institutua

Zarautz

Rafa Muñoa

Lizardi Institutua

Zarautz