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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 primary chemical difference between vegetable and animal fats lies in their saturation status. Animal fats are generally saturated, meaning they consist of single bonds in their fatty acid chains. In contrast, vegetable fats contain a higher amount of unsaturated bonds, which are characterized by double bonds. This distinction results in differing physical properties, such as melting point.
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 ethanal added?
Answer
Prior to the reflux, an anti-bumping agent should be added to the reaction flask to ensure smooth boiling and prevent bumping. The addition of ethanal provides a solvent for the lard, allowing for better interaction and facilitating the hydrolysis process.
Step 3
Why was it desirable to remove the ethanol after the reflux?
Answer
It was desirable to remove the ethanol after reflux to isolate the soap effectively. Ethanol can carry away some components, potentially impairing the purity of the soap. Moreover, its presence could interfere with subsequent steps and lead to a decrease in yield.
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 from the distillation to maximize the yield of soap that precipitates out when added to the brine. 'Brine' refers to a concentrated solution of salt (sodium chloride) in water, which aids in the precipitation of soap by reducing solubility.
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 filtering out the solid soap from the aqueous mixture of sodium hydroxide. After filtration, it is crucial to wash the isolated soap with ice-cold water to remove any residual sodium hydroxide. Using a pH indicator can help ensure that the soap is free of sodium hydroxide by confirming the neutralization of the soap.