Distillation and fractional distillation
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Distillation and fractional distillation — Free MYP4 Chemistry Practice Questions

1QuestionFractionating column and temperature gradientConcept Practice
2 marks~3 minCriterion A
A fractionating column separates crude oil using a temperature gradient: 350∘C350^\circ\text{C} at the base and 40∘C40^\circ\text{C} at the top. A mixture of hydrocarbon vapours enters at the bottom and rises through the column.
a
Explain how the temperature gradient drives vaporization and condensation as hydrocarbons rise through the column. [1]
b
Explain why different hydrocarbons condense at different levels within the column. [1]
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Solutions

2QuestionBoiling point differences in separationAssessment Practice
5 marks~8 minCriterion C
A student performs fractional distillation on a crude oil sample and collects three fractions, recording their boiling point ranges:

Fraction A: 70–85 °C70\text{–}85\ °C
Fraction B: 120–140 °C120\text{–}140\ °C
Fraction C: 340–400 °C340\text{–}400\ °C

Reference boiling points of pure alkanes:
Octane (C8H18C_8H_{18}): 125.6 °C125.6\ °C
Hexadecane (C16H34C_{16}H_{34}): 287 °C287\ °C

The student hypothesises that Fraction B is pure octane.
a
State the boiling point of pure octane and explain what a fixed, single boiling point indicates about the purity of a substance. [1]
b
Using the data provided, deduce whether Fraction B could contain hexadecane. Justify your answer with reference to the boiling point values. [2]
c
Evaluate the student's hypothesis that Fraction B is pure octane, using the boiling point range of Fraction B as evidence. [2]
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Solutions

3QuestionSimple distillation (separating solvent from solution)Concept Practice
3 marks~5 minCriterion B
A chemist needs to recover a solvent from a salt solution using simple distillation. The boiling points of three candidate solvents at standard atmospheric pressure are given below.

LiquidBoiling point (°C)
Water100
Ethanol78
Propanone56
a
State the trend in boiling points shown in the data. [1]
b
Identify which liquid would be most easily separated from a salt solution by simple distillation. [1]
c
Explain why a lower boiling point makes a liquid easier to separate from a salt solution using simple distillation. [1]

Solutions

4QuestionBoiling point differences in separationAssessment Practice
6 marks~9 minCriterion D
A biofuel plant uses fractional distillation to separate ethanol (boiling point 78 ∘C78\,^{\circ}\text{C}) from a fermentation broth containing water (boiling point 100 ∘C100\,^{\circ}\text{C}) and other organic compounds. The distillation column is heated continuously by burning natural gas.
a
Explain how the difference in boiling points between ethanol and water enables their separation by fractional distillation. [2]
b
Analyse how the energy requirement of the distillation column influences the overall carbon footprint of the biofuel plant. [2]
c
Evaluate whether fractional distillation powered by natural gas can be considered a genuinely sustainable method for biofuel production. [2]
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Solutions

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