AQA · Chemistry · 8462
GCSE Chemistry (AQA): Filtration & Crystalisation
Topic 1 — Atomic Structure & the Periodic Table. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Separation Techniques - Filtration | Evaporation | Crystallisation"; each card deep-links to the moment in the video it came from. Lesson 1.06 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_1.06.
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Why do more crystals form as a hot solution is left to cool?
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Solids are less soluble at lower temperatures, so the dissolved solid comes out of solution.
In salt water, water acts as the ?.
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solvent
In a solution, what is the solute?
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The substance that dissolves in the solvent — e.g. salt in salt water.
What is thermal decomposition?
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The breaking down of a substance into different substances when it is heated.
How does filter paper separate a mixture?
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Its tiny holes let liquid pass through but are too small for solid particles, which stay on the paper.
Why can filtration not separate a soluble solid from its solution?
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The dissolved solid passes through the filter paper with the solvent because it is no longer solid particles held back by the holes.
Why is evaporation unsuitable for some soluble solids?
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Strong heating can cause thermal decomposition, breaking the solid down into something else instead of isolating it.
What is a mixture in chemistry?
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Two or more different substances in the same place that are not chemically joined.
Which apparatus holds the solution during evaporation?
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An evaporating dish or a crucible, usually on a tripod above a Bunsen burner.
What is the final step of crystallisation after filtering off the crystals?
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Drying them — leaving them somewhere warm or using a drying oven.
Which separation technique is used for solids that decompose on heating?
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Crystallisation, because it uses gentler heating (e.g. a water bath) and cooling.
Which technique separates an insoluble solid from a liquid?
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Filtration.
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