Separation of mixtures
4 marks · Normal| Substance | Boiling point (°C) |
|---|---|
| Propane | -42 |
| Methanol | 65 |
| Ethanol | 78 |
| Water | 100 |
State which substance would be collected first if the mixture is separated by fractional distillation.
Explain why.
Two of the substances have boiling points within 13°C of each other. Identify them.
Suggest which technique should be used to separate the solid impurities from this mixture before distillation.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Propane · must show Propane
(b) Propane has the lowest boiling point, so it vaporises first. · must show lowest boiling point
(c) Methanol and ethanol · must show Methanol and ethanol
(d) Filtration · must show filtration
Also accept: Accept separation technique as 'filtration', 'gravity filtration', etc.
Common mistakes: Confusing which substance boils first; Choosing incorrect pair for (c)
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct: Propane
E1 (b) · 1 mark · Correct: lowest boiling point, so vaporises and collected first
B2 (c) · 1 mark · Identifies methanol (65°C) and ethanol (78°C) as within 13°C
B3 (d) · 1 mark · States filtration
Worked solution
a) Propane would be collected first.
b) It has the lowest boiling point (-42°C), so vaporises first in fractional distillation.
c) Methanol (65°C) and ethanol (78°C) are within 13°C of each other.
d) Filtration should be used to remove solid impurities.