A petroleum chemist must separate a 1.0 L solution that contains 25 % by volume of each of four liquids listed in the table. The solution behaves ideally.
Liquid
Normal boiling point (°C)
Pentane
36.1
Hexane
68.7
Heptane
98.4
Octane
125.6
The chemist will perform an initial distillation at 1.00 atm and monitor the temperature of the vapor above the boiling flask.
(a) During a simple distillation, which two liquids are expected to appear predominantly in the first 250 mL of distillate? Support your answer by relating boiling-point differences to relative vapor pressures.
(b) Explain why fractional, rather than simple, distillation would be required to obtain a sample of octane that is at least 95 % pure from the original mixture.
(c) Estimate the temperature range over which the distillation thermometer is likely to remain nearly constant while pentane is being collected. Provide a brief justification for your estimate.