Chemistry • Year 11 • Module 1 • Lesson 4
Separation Techniques — Advanced Methods
Lock in the vocabulary for distillation and chromatography, practise Rf calculations, and identify when each technique is appropriate before tackling harder questions.
1. Term–definition match
The definitions below are shuffled. In the right-hand column write the matching term from this list: simple distillation, fractional distillation, chromatography, stationary phase, mobile phase, Rf value, fractionating column, distillate, volatile, miscible. 10 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | Separation of a solvent from a dissolved solid (or a liquid from a non-volatile solute) by boiling and condensing the vapour. | |
| 1.2 | Separation of two or more miscible liquids with similar boiling points using a fractionating column to achieve multiple condensation/vaporisation cycles. | |
| 1.3 | A separation technique based on differential movement of components through a stationary phase carried by a mobile phase. | |
| 1.4 | The fixed material (e.g. filter paper or silica) through which the mobile phase moves during chromatographic separation. | |
| 1.5 | The solvent that moves through the stationary phase, carrying dissolved components with it at different speeds. | |
| 1.6 | The ratio of the distance moved by a component to the distance moved by the solvent front; always between 0 and 1. | |
| 1.7 | The column packed with glass beads or rings that allows multiple vaporisation/condensation cycles in fractional distillation. | |
| 1.8 | The liquid product collected in the receiver after vapour passes through the condenser and cools. | |
| 1.9 | Having a low boiling point and evaporating readily at room temperature. | |
| 1.10 | Describes two liquids that are completely soluble in each other in all proportions (e.g. ethanol and water). |
2. True or false — with correction
Circle T or F for each statement. If the statement is false, write the corrected version on the line below it. 12 marks (1 T/F + 1 correction each)
2.1 Simple distillation can effectively separate a mixture of ethanol (BP 78°C) and water (BP 100°C). T / F
2.2 The Rf value of a compound can exceed 1 if the compound moves faster than the solvent front. T / F
2.3 In chromatography, a component with a high Rf value has a stronger attraction to the mobile phase than to the stationary phase. T / F
2.4 Salt water should be separated by fractional distillation rather than simple distillation because salt has a boiling point close to water. T / F
2.5 A compound’s Rf value is characteristic for a given stationary phase and mobile phase under identical conditions. T / F
2.6 In paper chromatography, the Rf value is calculated by measuring from the solvent front to the centre of the spot. T / F
3. Fill-in-the-blank paragraph
Use the word bank to complete the passage. Each word is used once. 8 marks (1 per blank)
Word bank:
boiling point · condenser · fractional · fractionating column · mobile phase · origin · Rf · stationary phase
Distillation separates liquids based on differences in ___________. Simple distillation involves heating a mixture so the more volatile component vaporises; the vapour then passes into a ___________, where it is cooled and collected as the distillate. When two miscible liquids have similar boiling points, ___________ distillation is required. The ___________ provides multiple vaporisation and condensation cycles along its length, progressively enriching the vapour in the more volatile component. In chromatography, components are separated by their differential attraction to the ___________ and the ___________. The ___________ value is calculated as the distance a component travels from the ___________ divided by the distance the solvent front travels from the same point.
4. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 What is the function of the fractionating column in fractional distillation?
4.2 Why must both distances in an Rf calculation be measured from the origin (baseline) rather than from the bottom of the paper?
4.3 What property difference between components makes distillation work as a separation technique?
4.4 Why can Rf values only be used to identify a compound when the same solvent and stationary phase are used as in the reference standard?
5. Label the distillation apparatus
The diagram below shows a simple distillation setup. Write the correct component name for each label A–F in the table. 6 marks (1 each)
| Label | Component name |
|---|---|
| A | |
| B | |
| C | |
| D | |
| E | |
| F |
Q1 — Term–definition match
1.1 simple distillation • 1.2 fractional distillation • 1.3 chromatography • 1.4 stationary phase • 1.5 mobile phase • 1.6 Rf value • 1.7 fractionating column • 1.8 distillate • 1.9 volatile • 1.10 miscible.
Q2 — True / false with correction
2.1 False. The BP difference between ethanol (78°C) and water (100°C) is only 22°C — too small for simple distillation to achieve adequate separation. Fractional distillation with a fractionating column is required.
2.2 False. Rf values are always between 0 and 1 because no component can travel further than the solvent front. Rf = component distance ÷ solvent front distance; the maximum value is 1 (moves with the solvent front).
2.3 True. A high Rf means the component moved further, indicating stronger attraction to (greater solubility in) the mobile phase relative to the stationary phase.
2.4 False. Salt water should be separated by simple distillation. Salt (sodium chloride) is a non-volatile solid with a boiling point far above that of water (>800°C); it does not compete with water for the vapour phase, so a fractionating column is unnecessary.
2.5 True. Rf values are characteristic per compound only under identical experimental conditions (same solvent, stationary phase, temperature, and plate/paper type).
2.6 False. Both distances — the component distance and the solvent front distance — are measured from the origin (baseline), not from the solvent front. Rf = (distance from origin to spot centre) ÷ (distance from origin to solvent front).
Q3 — Cloze paragraph
In order: boiling point / condenser / fractional / fractionating column / stationary phase / mobile phase / Rf / origin.
Q4.1 — Function of fractionating column
The fractionating column provides many successive vaporisation and condensation cycles along its length. This gradually enriches the vapour in the more volatile (lower-boiling) component, so that the vapour reaching the condenser is predominantly the more volatile substance, allowing adequate separation of liquids with close boiling points.
Q4.2 — Why measure from the origin
Both distances must be measured from the origin because the solvent (and the spot) starts at the origin and travels upward; the origin is the reference point for both distances. Measuring from the bottom of the paper (which includes the part below the baseline that was submerged in solvent) would give incorrect, non-reproducible values.
Q4.3 — Property difference for distillation
Distillation exploits differences in boiling point (volatility) between components. The component with the lower boiling point vaporises preferentially when the mixture is heated; this vapour is then condensed and collected separately from the less volatile residue.
Q4.4 — Why same conditions are required for Rf comparison
Rf values depend on the relative attraction of a compound to the specific stationary phase and mobile phase being used. Different solvents or stationary phases change the relative affinities, altering how far each compound migrates. An Rf measured in one solvent system will differ from one measured in another, making cross-condition comparisons meaningless.
Q5 — Label the distillation apparatus (A–F)
A: Round-bottom flask (contains the mixture being heated). B: Heat source (Bunsen burner / heating mantle). C: Thermometer (measures vapour temperature at the still head). D: Liebig condenser / water-cooled condenser (cools vapour back to liquid). E: Receiver flask (collects the distillate). F: Distillate (condensed liquid product). Accept reasonable synonyms; credit the correct component in any reasonable label order.