CSEC Chemistry • Lesson 4 of 4Separation Techniques & Sucrose Extraction · Myers Science Hub Student Centre
CourseCSEC Chemistry
Practice formatMCQ • Structured • Experimental
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Learning objectives
- Select filtration, crystallisation, distillation, fractional distillation, chromatography or a separating funnel for a stated mixture.
- Explain the property difference used by each method.
- Interpret simple chromatograms and separation diagrams.
- Describe the main stages in extracting sucrose from sugar cane.
Core notes
Choose a separation method from a property difference
| Property difference | Technique | Typical example |
|---|---|---|
| Particle size / insolubility | Filtration | sand from water |
| Solubility / crystal formation | Crystallisation | salt crystals from solution |
| Boiling point | Simple distillation | solvent from a solution |
| Different but relatively close boiling points | Fractional distillation | miscible liquids |
| Immiscible liquid layers | Separating funnel | oil and water |
| Different solute mobility in a solvent | Paper chromatography | dyes in ink |
Chromatography
The solvent rises through the paper and carries soluble substances at different rates. A substance that is more strongly attracted to the mobile phase generally moves farther than one more strongly attracted to the paper.
Caribbean context: sucrose from sugar cane
A simplified sequence is crushing the cane, treating/precipitating impurities, filtration, concentrating the juice by vacuum evaporation/distillation, crystallisation, then centrifugation to separate sugar crystals from the remaining syrup.
Video lesson
Paper 01-style MCQ
1. Which method is most suitable for separating two immiscible liquids of different densities?KC • 1
2. Which property is used mainly in simple distillation?KC • 1
3. In paper chromatography, two dyes travel different distances mainly because they have differentUK • 1
Paper 02-style structured questions
4. A mixture contains sand, sodium chloride and water. Describe how to obtain dry sodium chloride crystals from the mixture.UK • 6
Filter to remove sand (1); collect the filtrate containing sodium chloride solution (1); heat/evaporate some water to concentrate (1); allow the concentrated solution to cool so crystals form (1); filter/remove the crystals (1); dry the crystals between filter papers/in a suitable warm place (1).
5. Explain why fractional distillation is preferred to simple distillation for separating two miscible liquids with relatively close boiling points.UK • 3
A fractionating column provides repeated evaporation and condensation (1), improving separation (1), which is needed because the boiling points are close and vapours would otherwise overlap strongly (1).
Experiment-type question
6. A student is given black ink and asked to determine whether it contains more than one dye. Plan a paper chromatography experiment.XS/PD • 8
Spot a small amount of ink on a pencil baseline above solvent level (1); place paper in suitable solvent without submerging the spot (1); cover container where appropriate (1); allow solvent to rise (1); remove before solvent reaches top and mark solvent front (1); dry and observe separated spots (1); conclude more than one dye if more than one spot forms (1); include a suitable solvent/safety precaution (1).