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Separating and purifying substances
Separating and purifying substances
The separation method depends on:
the type of mixture
which substance in the mixture we are most interested in
Separating insoluble solids from liquids
DECANTING: once the solid has settled to the bottom, the liquid can be carefully poured off.
FILTRATION: separating solid from liquid collecting a residue on a filter paper. Both phases are obtained in one process, the liquid collected is called filtrate.
CENTRIFUGATION: where a mixture is spun at high speed in a centrifuge, this causes the solid to be deposited at the bottom of the centrifuge tube.
Separating immiscible liquids
mixture placed in a separating funnel and allowed to stand, it will separate in different layers
the lower denser will be at the bottom
Separating mixtures of solids
physical properties needs to be found (density, magnetic properties or sublimation)
usually is used on the base of difference in solubility
Separations based on differences in solubility
CRISTALLISATION:
first ground to a powder
a liquid solvent is added
the solvent must dissolve only one of the solid substances
mixture is warmed and then stirred
warmed mixture is then filtered
dry crystals can be obtained
Separating solutions
no physical separation of the phases in the original mixture
depends on solubility and boiling point
DISTILLATION: The different boiling point makes possible the separation by evaporation of the most volatile solution that will pass through the condenser getting in a flask and collected as the distillate.
FRACTIONAL DISTILLATION: used to separate any solution containing liquids with different boiling points. The liquid in the mixture with the lowest boiling point (most volatile) distils over first. The final liquid to distil over is the one with the highest boiling point (least volatile).
It is used as a fractionating column for collecting the most volatile (lowest boiling point) as vapour one in order to provide a large surface area for condensation.
SEPARATING TWO OR MORE SOLIDS IN A LIQUID → CHROMATOGRAPHY
tells us whether a solution has become contaminated
a drop of concentration is placed on a line near the edge of the paper
paper is dipped in the solvent
the level of the solvent rises taking different components at different rates
many different solvent can be used
the substance separate according to their solubility in the solvent
the run is stop when the solvent front reaches the top of the paper
ratio of distances = distance moved by the substance / distance moved by the solvent front
The purity and identity of substances
Paper chromatography can be used to check the purity of a substance. If the sample is pure, it should give only one spot when run in several different solvents.
THE SOLUBILITY OF SOLIDS IN LIQUIDS
If a substance dissolves in a solvent is said to be soluble while if it doesn't it is insoluble.
a concentrated solution contains high proportion of solute while a dilute contains a small proportion of solute
CONCENTRATION: the mass of the solute dissolved in a particular volume of solvent
If we keep adding solid, we will reach a point where the solution will become saturated.
the concentration of solute in a saturated solution is the solubility of the solute at that temperature
THE SOLUBILITY OF GASES IN LIQUIDS
solubility of gases from the air in water is quite small
the solubility of gases increases with pressure
carbon dioxide is more soluble than oxygen or nitrogen
substances are not only mixing but also reacting
video-output-0E087FF8-24CF-4A62-9473-B9689921AE07.movExperiment on centrifugation we have done in the lab
Video Cromatografia.mp4Experiment on chromatography we have done in the lab
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