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A liquid mixture of 50% ethanol and 50% water was distilled in the apparatus shown above - VCE - SSCE Chemistry - Question 19 - 2009 - Paper 1
Question 19
A liquid mixture of 50% ethanol and 50% water was distilled in the apparatus shown above. The boiling point of ethanol is 78°C and that of water is 100°C. As the mi... show full transcript
Worked Solution & Example Answer:A liquid mixture of 50% ethanol and 50% water was distilled in the apparatus shown above - VCE - SSCE Chemistry - Question 19 - 2009 - Paper 1
Step 1
The percentages of ethanol in the vapours at X, Y and Z.
Answer
At the boiling point of 78°C, ethanol will vaporize preferentially compared to water since it has a lower boiling point. During distillation, the vapour composition will change as the temperature reaches equilibrium.
- At point X (just above the boiling pot), the vapour will be rich in ethanol due to its lower boiling point; hence, it may be slightly above 50%.
- At point Y, the temperature is maintained at 78°C, and the vapour composition will continue to favor ethanol, but less so than at X due to dilution from water vapour.
- At point Z (the condenser exit), the ethanol concentration will be lower than at Y, but still higher than 47% since ethanol has started to condense to liquid but is not exclusively water.
Therefore, the only correct statement here is C: The percentages of ethanol in the vapours at Y and Z are equal but greater than 47%.