E. Learn eXP Flashcards
Esterification
A carboxylic acid + an alcohol → An ester + water
Why is saponification also considered a condensation reaction?
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.
An ester
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.
Limiting reactant in saponification
Glycerol tristearate
Describe the cleansing action of soap.
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.
Ester used (saponification)
Lard
Why was the apparatus set up for reflux? (saponification)
Ensures time for the complete saponification reaction without losing any volatile material.
Why is ethanol used? (saponification)
As a solvent for the lard
What was used to filter the soap?
A Buchner funnel
What is the principal chemical difference between vegetable and animal fats?
Animal saturated, vegetable unsaturated
Why was it desirable to remove the ethanol after reflux? (saponification)
Easier to isolate soap to maximize yield
Why was a minimum of hot water used to dissolve the residue from the distillation? What is brine. (saponification)
- To maximise soap precipitating out (yield)
- A (concentrated) salt solution
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)
- Filter
- Wash with ice-cold water
Describe how a pure sample of soap was obtained from the reaction mixture.
- Dissolve residue in a minimum of boiling water,
- Pour onto brine, filter
- Wash with ice-cold water
At the end of the experiment what is the location of the second product of the reaction? (saponification)
In the brine / Buchner flask
At the end of the experiment what is the location of the excess sodium hydroxide? (saponification)
In the brine / Buchner flask
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)
No bubbles
What substance was removed by distillation in Stage 2? (saponification)
Ethanol
Explain the function of the brine in Stage. (saponification)
To precipitate the soap
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.
C17H35 is non-polar and dissolves oils
-COO-Na+ attracted to salts in sweat
Give the name of the co-product of the reaction and where was it location at the end of the process. (saponification)
Glycerol - in the brine
State one way of maximising the yield of the recrystallisation process. (prep of benzoic acid)
Use minimum amount of boiling water
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)
- HCL and Na2SO3
- Dark brown decolourises and white crystals form
