A group of students prepared a sample of soap in a school laboratory - Leaving Cert Chemistry - Question 1 - 2007
Question 1
A group of students prepared a sample of soap in a school laboratory. A mixture of about 4 g of fat, 2 g of sodium hydroxide and 25 cm³ of ethanol was refluxed for a... show full transcript
Worked Solution & Example Answer:A group of students prepared a sample of soap in a school laboratory - Leaving Cert Chemistry - Question 1 - 2007
Step 1
Which of the arrangements of apparatus (A or B) was used for: (i) the reflux
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Answer
The arrangement of apparatus B was used for the reflux. This is because B allows for the condensation of vapors back into the reaction flask, effectively preventing loss of the reactants and ensuring that the reaction proceeds efficiently.
Step 2
Which of the arrangements of apparatus (A or B) was used for: (ii) the distillation stage of the preparation?
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Answer
The arrangement of apparatus A was used for the distillation stage. This setup is designed to efficiently separate components based on their boiling points.
Step 3
Draw: A rough sketch of either arrangement and append to your answer-book and clearly indicate which part of the condenser should be connected to the cold water tap.
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A sketch should be made showing either apparatus A or B with a clear indication of the water intake point connected to the lower intake of the condenser. Ensure that the drawing appropriately labels each part.
Step 4
Why was ethanol added to the fat and the sodium hydroxide?
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Ethanol acts as a solvent in this reaction. It helps to dissolve the reactants, allowing for better mixing and interaction between the fat and sodium hydroxide, which is essential for the saponification process.
Step 5
Why was a small amount of boiling water used to dissolve the soap remaining in the distillation flask?
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Using boiling water helps to maximize the yield by dissolving the soap more effectively and minimizing loss. Warm water allows for better solubility of the soap, ensuring more product is recovered.
Step 6
When the soap was collected by filtration it was washed with water.
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The washing process ensures the removal of any impurities or residual chemicals, particularly sodium hydroxide, which may still be present in the soap.
Step 7
What: (i) would happen to the soap?
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The soap would lather effectively in water.
Step 8
What: (ii) what would you expect to observe if the water used was (1) from a hard water region?
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If the water used was from a hard water region, it would likely form no lather, and instead, a scum or ppt (precipitate) may be observed due to the presence of calcium or magnesium ions that react unfavorably with the soap.
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