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, (ii) the distillation stage of the preparation?
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Answer
For the reflux stage, apparatus B was used, while for the distillation stage, apparatus A was utilized.
Step 2
Draw a rough sketch of either arrangement of apparatus in your answer-book and clearly indicate which part of the condenser should be connected to the cold water up.
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Answer
The drawing should show a clear sketch of the chosen apparatus arrangement, indicating that the lower intake point of the condenser is connected to the cold water supply.
Step 3
Why was ethanol added to the fat and the sodium hydroxide? What else could have been used?
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Answer
Ethanol was added as a solvent to aid in the dissolution of the fat and sodium hydroxide. Other solvents, such as methanol, could also have been used for this purpose.
Step 4
Why was only a small amount of boiling water used to dissolve the residue remaining in the distillation flask?
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Answer
Only a small amount of boiling water was used to minimize the loss of soap and increase the yield of the final product.
Step 5
When the soap was collected by filtration it was washed with a little ice-cold water. Why is it important to wash the soap?
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Washing the soap is important to remove any residual sodium hydroxide that may be present, ensuring the soap is safe for use.
Step 6
What amount of the soap produced in this experiment was added to test tubes containing different sweeteners and the mixtures were shaken. What would you expect to observe if the water was used?
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If the water was used in the experiment, one would expect to observe no lather or scum formation, indicating that the soap does not react with distilled water.
Step 7
from a hard water region
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Answer
If the soap were tested with hard water, it would likely form a scum or precipitate, as the calcium and magnesium ions in hard water react with the soap to form insoluble salts.
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