An environmental field laboratory is located at a mountain site where the ambient pressure averages 0.80 atm. A technician plans to separate an equimolar mixture of three liquids by simple distillation under the local pressure. Empirical data for each substance are provided.
Liquid
Normal boiling point at 1.00 atm (°C)
Boiling-point change per 0.10 atm decrease in pressure (°C)
Acetone
56.5
−3.0
Water
100.0
−1.0
Ethylene glycol
197.5
−0.5
Assume the rate of change listed remains constant over the pressure range involved.
(a) Calculate the approximate boiling point of each liquid at 0.80 atm. Show your work, including units.
(b) Predict the order in which the three liquids will be collected during the distillation at 0.80 atm. Justify your answer quantitatively with the values from part (a).
(c) Compare the predicted order at 0.80 atm with the order expected at 1.00 atm, and explain any difference or lack thereof in terms of the relative sensitivity of each liquid’s boiling point to pressure changes.