Filtration and crystallisation
Learn more on filtration, evaporation and crystallisation in this podcast.
Listen to the full series on 大象传媒 Sounds.
Filtration
Method used to separate an insoluble solid from a liquid using a physical barrier such as paper. is used to separate an Unable to dissolve in a particular solvent. For example, sand is insoluble in water. solid from a liquid. It is useful for separating sand from a mixture of sand and water, or In chemistry, a substance is in excess if there is more than enough of it to react with another reactant. A substance that reacts together with another substance to form products during a chemical reaction. from a reaction mixture.
Filtration works because the filter paper has tiny holes or pores in it. These are large enough to let small A collection of two or more atoms held together by chemical bonds. and A substance is said to be dissolved when it breaks up and mixes completely with a solvent to produce a solution. Electrically charged particle, formed when an atom or molecule gains or loses electrons. through, but not the much larger particles of undissolved solid.
Image caption, Separating insoluble solids
1. One beaker contains a mixture of solid and liquid, the other contains a funnel with filter paper
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Crystallisation
The process of producing crystals from a solution by evaporating the solvent. is used to produce solid A solid containing particles (atoms, molecules or ions) joined together to form a regular arrangement or repeating pattern. from a Mixture formed by a solute and a solvent.. When the solution is warmed, some of The liquid in which the solute dissolves to form a solution. The process in which a liquid changes state and turns into a gas. leaving crystals behind. For example, crystallisation is used to obtain copper sulfate crystals from copper sulfate solution.
Image caption, 1. A solution is placed in an evaporating basin and heated with a Bunsen burner.
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To obtain large, regularly shaped crystals from crystallisation:
- put the solution in an evaporating basin
- warm the solution by placing the evaporating basin over a boiling water bath
- stop heating when crystals begin to form around the edge of the basin
After the remaining solution has cooled down, pour the excess liquid away (or filter it). Dry the crystals using a warm oven or by patting them with filter paper.