E. Learn eXP

Question 1

Esterification

Answer 1

A carboxylic acid + an alcohol → An ester + water

Question 2

Why is saponification also considered a condensation reaction?

Answer 2

As it involves the reaction of two different molecules to produce a more complex molecule, with the production of a smaller molecule such as water.

Question 3

An ester

Answer 3

A molecule that is formed when the hydrogen of the functional group of a carboxylic acid is replaced by an alkyl radical of an alcohol.

Question 4

Limiting reactant in saponification

Answer 4

Glycerol tristearate

Question 5

Describe the cleansing action of soap.

Answer 5

The oils that our skin produces dissolve in the non-polar carbon chain of the soap and the salts that our skin produces dissolve in the polar functional group.

Question 6

Ester used (saponification)

Answer 6

Lard

Question 7

Why was the apparatus set up for reflux? (saponification)

Answer 7

Ensures time for the complete saponification reaction without losing any volatile material.

Question 8

Why is ethanol used? (saponification)

Answer 8

As a solvent for the lard

Question 9

What was used to filter the soap?

Answer 9

A Buchner funnel

Question 10

What is the principal chemical difference between vegetable and animal fats?

Answer 10

Animal saturated, vegetable unsaturated

Question 11

Why was it desirable to remove the ethanol after reflux? (saponification)

Answer 11

Easier to isolate soap to maximize yield

Question 12

Why was a minimum of hot water used to dissolve the residue from the distillation? What is brine. (saponification)

Answer 12

• To maximise soap precipitating out (yield)

- A (concentrated) salt solution

Question 13

Describe how the soap could be isolated from the mixture of soap and brine. Give one precaution that helps to ensure that the soap is free of sodium hydroxide. (saponification)

Answer 13

• Filter

- Wash with ice-cold water

Question 14

Describe how a pure sample of soap was obtained from the reaction mixture.

Answer 14

• Dissolve residue in a minimum of boiling water,
• Pour onto brine, filter
• Wash with ice-cold water

Question 15

At the end of the experiment what is the location of the second product of the reaction? (saponification)

Answer 15

In the brine / Buchner flask

Question 16

At the end of the experiment what is the location of the excess sodium hydroxide? (saponification)

Answer 16

In the brine / Buchner flask

Question 17

What would you observe, upon shaking, if a little of the soap prepared in this experiment is added to a test tube containing mineral water from a limestone region? (saponification)

Answer 17

No bubbles

Question 18

What substance was removed by distillation in Stage 2? (saponification)

Answer 18

Ethanol

Question 19

Explain the function of the brine in Stage. (saponification)

Answer 19

To precipitate the soap

Question 20

Suggest, with reference to its structure, how a soap like sodium stearate can dissolve both the non-polar oils and the ionic salts in sweat from the skin.

Answer 20

C17H35 is non-polar and dissolves oils

-COO-Na+ attracted to salts in sweat

Question 21

Give the name of the co-product of the reaction and where was it location at the end of the process. (saponification)

Answer 21

Glycerol - in the brine

Question 22

State one way of maximising the yield of the recrystallisation process. (prep of benzoic acid)

Answer 22

Use minimum amount of boiling water

Question 23

Identify two substances that were added to allow separation of the benzoic acid from the other substances after the oxidation was complete? What changes were observed on addition of these chemical and as cooling occurred? (prep of benzoic acid)

Answer 23

• HCL and Na2SO3

- Dark brown decolourises and white crystals form