Separation methods and chromatography
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 1 worked example, 4 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Pull it apart
- The words
- More words
- Filtration
- Crystallisation
Read the transcript of the teaching part
Last time
Before we start: last time, in Tests for ions and gases; identifying a compound, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Pull it apart
Sea water, black ink, crude oil, muddy tea. Nearly everything we use starts as a mixture. Chemists have a toolbox of methods for pulling mixtures apart, and the skill is to pick the right one by looking at how the parts differ.
The words
A solute is the substance that dissolves. The solvent is the liquid it dissolves in. Together they make a solution. A saturated solution holds as much solute as it can at that temperature. A substance that dissolves is soluble. One that does not dissolve is insoluble.
More words
In filtration, the solid left on the filter paper is the residue. The liquid that passes through is the filtrate. Two liquids that mix completely are miscible. Two that form separate layers are immiscible.
Filtration
Use filtration to separate an insoluble solid from a liquid, such as sand from water. The solid is trapped by the filter paper, and the liquid passes through. Wash the residue with a little distilled water, and dry it.
Crystallisation
Heat the solution to evaporate some water, until it is saturated. A drop on a glass rod forms crystals when it cools. Leave the hot solution to cool slowly. Crystals form. Filter them off, wash, and dry. Do not boil it dry. That makes a powder, and may decompose the crystals.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Choosing a separation method · Paper chromatography method · Solution and separation terms · Paper chromatography · Separation and purification.
The whole chapter: Experimental Techniques and Chemical Analysis, Experimental Techniques and Chemical Analysis.
Chapter 12: Experimental techniques
- Separation methods and chromatography 6 min
- Tests for ions and gases; identifying a compound 6 min
Also for IGCSE Chemistry 0620
Which topics come up most in IGCSE Chemistry 0620 past papers, counted from every paper since 2004.