mixtures and separation methods

mixtures

elements or compounds not chemically bonded together.

Paper Chromatography - Method

can be used to separate different dyes in an ink based on their different solubilities.
1. use pencil to draw line near bottom of filter paper (pencil is insoluble).
2. add spot of ink to line and place sheet into beaker of solvent. solvent depends on substance tested. ensure solvent placed below pencil line so doesn't dissolve ink.
3. place lid to prevent solvent evaporating. solvent will climb up paper and different dyes on ink will move at different rates so spread out in different places.
4. pure substances will only have one spot in any solvent. insoluble dyes will stay at baseline.
5. when solvent has nearly reached top, take paper out and dry. result is called a chromatogram.

phases in chromatography

paper is stationary phase and solvent is mobile phase.
point that solvent reaches on paper is the solvent front.

filtration

used to separate an insoluble solid from a liquid mixture and in purifying to separate solid impurities.
use filter paper folded in a cone shape on a beaker and slowly pour mixture into cone. the liquid in the beaker is the filtrate and the solids are the residue.

two methods used to separate soluble solids from solutions

evaporation and crystallisation.
pour solution into evaporating dish and slowly heat with bunsen burner.

evaporation method

when heated with bunsen burner, solvent will evaporate and become more concentrated until left with dry crystals.

crystallisation method

when heating with bunsen burner, remove dish from heat once some of solvent has evaporated or crystals start to form. when it cools salt forms crystals and becomes insoluble. filter crystals out and leave in a warm place to dry. could use a drying oven or desiccator.

simple distillation method

used to separate a liquid from a solution. for example water from seawater.
1. solution is heated. part with lowest boiling point evaporates first.
2. vapour is cooled and condenses. is collected in a beaker. rest of solution is left behind in flask.

problems with simple distillation

can only be used if substances have very different boiling points as if temp goes higher than highest bp then they will mix.

fractional distillation

used to separate a mixture of liquids with similar boiling points.
1. put mixture in a flask under a fractionating column. heat it.
2. different liquids will evaporate at different boiling points so liquid with lowest boiling point evaporates first. when temp on thermometer matches it will reach the top of column.
3. other liquids may also start to evaporate but is cooler at top so will condense beforehand.
4. once liquid has been collected raise temperature and repeat.