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C2.2 Separating and purifying substances - Coggle Diagram
C2.2 Separating and purifying substances
Separating insoluble solids from liquids
Separaations can be based on
differences in
Density
Solubility
Sublimation
Magnetic properties
Mixture of iron and copper
Separating immiscible liquids
Mixtures of two immiscible liquids can be separated into different layers. The lower, denser layer is then tapped off at the bottom
Mixture of oil and water
Separating mixtures of solids
Decanting
Once the solid has settled to the bottom, the liquid can be carefully poured off
Filtration
Refine to obtain in one process
Residue
The insoluble material is collected on filter paper
Filtrate
The liquid phase is collected
Centrifugation
The mixture is spun at high speed in a centrifuge. The solid to be deposited at the bottom of the centrifuge tube. The liquid can be carefully decanted off
Mixture of sand and water
Separations based on
differences in solubility
The dissolve one of the solid substances present but not the others
The mixture is then filtered
The insoluble substances as a residue on the filter paper which can be dried
The soluble substance is in the liquid filtrate. Dry crystals can be obtained by evaporation and crystallisation
Separating solutions
Separating a liquid from a solution
Distillation
Distillate
The liquid is more volatile than the dissolved solid and can easily be evaporated off in a distillation flask
Separating a solid from solution in a liquid
Can be carried out by
Evaporation
Evaporation gives only a powder. Evaporation is stopped when the solution has been concentrated enough
Crystallisation
Crystallisation can result in crystals. The concentrated solution is allowed to cool slowly. The crystals formed can be filtered off and dried
Separating the liquids from a mixture of two
or more miscible liquids
Fractional distillation
FD is used to separate any solution containing liquids with different boiling points
The liquid in the mixture with the loweest boiling point (the most volatile) distils over first.
The final liquid to distil over is the one with the highest boiling point (the least volatile)
Separating two or more dissolved solids in solution
can be carried out by chromatography to analyse the substances present in a solution
The substances separate according to their solubility in the solvent. As the solvent moves up the paper, the substances are carried with it and begin to separate
The substance that is most soluble moves fastest up the paper. An insoluble substance would remain at the origin
The purity and identity of substances
Paper chromatography is one test that can be used to check for the purity of a substance
The most generally used tests for purity are measurements of melting point or boiling point
A closer look at solutions
Soluble
A substance dissolves in a solvent
Insoluble
A substance does not dissolve
Concentrated
A solution contains a high proportion of solute
Dilute
A solution contains a small proportion of solute
Concentration
The concentration of a solution is the mass of solute dissolved in a particular volume of solvent, usually 1 mL
Saturated solution
A point is reached when no more will dissolve at that temp
Solubility
The concentraton of solute in a saturated solution is the solubility of the solute at that temp
The solubility of gases in liquids
Unlike most solids, gases become less soluble in water as the temp rises
The solubility of gases increases with pressure
Carbon dioxide is more soluble than either nitrogen or oxygen because it reacts with water to produce carbonic acid