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Soap is produced by the hydrolysis of vegetable and animal fats - Leaving Cert Chemistry - Question 2 - 2002
Question 2
Soap is produced by the hydrolysis of vegetable and animal fats. (a) What is the principal chemical difference between vegetable and animal fats? (5) A sample of s... show full transcript
Worked Solution & Example Answer:Soap is produced by the hydrolysis of vegetable and animal fats - Leaving Cert Chemistry - Question 2 - 2002
Step 1
What is the principal chemical difference between vegetable and animal fats?
Answer
The principal chemical difference between vegetable and animal fats lies in their saturation. Animal fats are generally saturated, consisting of all single bonds in their fatty acid chains, while vegetable fats usually contain unsaturated bonds (double bonds). This results in different physical properties and degrees of saturation.
Step 2
Apart from the lard, sodium hydroxide and ethanol, what else should be added to the reaction flask prior to the reflux? Why was the acid added?
Answer
An anti-bumping agent should be added to the reaction flask prior to the reflux. This is important because it helps to ensure smooth boiling during the reaction process, preventing the formation of large bubbles which can cause sudden and vigorous boiling. The addition of acid, such as hydrochloric acid, is crucial as it aids in the complete hydrolysis of the fat and neutralizes excess sodium hydroxide.
Step 3
Why was it desirable to remove the ethanol after the reflux?
Answer
It is desirable to remove the ethanol after reflux because it is a volatile component that does not contribute to the final soap product. The presence of ethanol can interfere with the isolation of the soap and might affect its purity. Removing ethanol also helps to concentrate the soap solution for better extraction.
Step 4
Why was a minimum of hot water used to dissolve the residue from the distillation? What is brine?
Answer
A minimum of hot water was used to dissolve the residue to ensure that the soap precipitates fully and does not remain dissolved. The use of hot water minimizes the solubility of the soap in the water, promoting the maximum yield of soap. Brine is a concentrated solution of sodium chloride (salt) in water, which helps to precipitate the soap out of the solution.
Step 5
Describe how the soap could be isolated from the mixture of soap and sodium hydroxide. Give one precaution that helps to ensure that the soap is free of sodium hydroxide.
Answer
The soap can be isolated by first filtering the mixture to separate the solid soap from the liquid sodium hydroxide solution. After filtration, the soap can be washed with cold water to remove any remaining sodium hydroxide. One precaution to ensure that the soap is free of sodium hydroxide is to use an indicator, such as phenolphthalein, to test the pH of the soap. If the soap is basic, additional washing is necessary.