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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 increase in order at positions X, Y and Z.
Answer
When the liquid mixture is heated to the boiling point of ethanol (78°C), ethanol starts to vaporize first, as it has a lower boiling point compared to water. This leads to a higher concentration of ethanol in the vapours at point X, immediately above the boiling flask.
As the vapour rises through the condenser towards Y and then Z, the concentration of ethanol will vary. At point Y, a certain amount of the vapour will start to condense back into the liquid. This means that at Y, the concentration of ethanol will be higher than at X, since more ethanol has evaporated than water due to its lower boiling point.
At Z, where the vapours exit, the concentration of ethanol would still be greater due to the continuous heating process, thus confirming that the vapour concentrations increase from X to Y to Z.