Separating Mixtures: Distillation and Chromatography
Select and carry out appropriate separation techniques for different types of mixtures: filtration (insoluble solids), distillation (liquids by boiling point), crystallisation (dissolved solids), and chromatography (coloured substances)
What a learner can do afterwards
- Selects the correct separation technique for a given mixture with justification
- Describes the steps of simple distillation and explains why it works
- Interprets a chromatography result (Rf values, number of components)
- Explains why filtration removes sand from water but not salt
1 · Read
A mixture has more than one substance in it. To pull the parts apart, pick the technique that matches how the parts differ. Filtration uses size: it traps a solid that never dissolved. Crystallisation uses solubility: drive the solvent off and the dissolved solid is left behind. Distillation uses boiling point. Chromatography uses how far a substance travels in a solvent.
Imagine sand and salt mixed into water. First you pour it through filter paper. Sand grains are too big to fit through the tiny holes, so they stay on the paper. That is filtration. The salty water passes straight through, because the salt has dissolved into particles far smaller than the holes. To get the salt back, you heat that salty water gently until the water turns to vapor and floats away, leaving solid salt crystals in the dish. This second step is called crystallisation.
Distillation works because different liquids boil at different temperatures. Heat the mixture and the liquid with the lower boiling point turns to vapor first. That vapor travels through a cooled tube called a condenser, turns back into liquid, and drips into a separate container. What is left behind stays in the flask.
Chromatography works on colored substances. A drop of the mixture sits near the bottom of the paper, and a solvent creeps up past it. Each substance travels its own distance, so each one ends up as its own spot. Count the spots and you have counted the substances. Divide the distance a spot traveled by the distance the solvent traveled, and you get that spot's Rf value, always a number between 0 and 1.
Match the technique to the mixture: filtration for solids you can see, crystallisation for a dissolved solid, distillation for liquids with different boiling points, and chromatography for colored substances.
2 · Watch
Take it off screen
Where it sits
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.