1.4 Separation techniques Flashcards
Explain the following: solute,
solvent, solution, miscible, immiscible, soluble, insoluble.
A solute is a substance that is dissolved in a solvent. Together, they form a
solution.
Miscible refers to the substances (particularly liquids) that mix together, e.g. water and alcohol. Water and oil are immiscible, i.e. they do not mix.
Soluble refers to the substance that can be dissolved in a solvent, e.g. salt in
water. An insoluble substance won’t dissolve in a particular solvent.
What is a mixture? Does it have the
same chemical properties as its
constituent materials?
A mixture consists of two or more elements or compounds not chemically
combined together; it does have the same chemical properties
What are the methods through
which mixtures can be separated
(5)? Do these involve
chemical reactions?
Filtration, crystallisation, simple distillation, fractional distillation and
chromatography; they do not involve chemical reactions
Describe and explain simple
distillation.
Simple distillation is used to separate liquid from a solution – the liquid
boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid
Describe and explain
crystallisation/evaporation.
Evaporation is a technique for separation of a solid dissolved in a solvent from a
solvent (e.g. salt from H2O).
The solution is heated until all the solvent evaporates; the solids stays in the vessel.
Crystallisation is similar, but we only remove some of the solvent by evaporation to
form a saturated solution (the one where no more solid can be dissolved). Then,
we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration.
Describe and explain
fractional distillation
Fractional distillation is a technique for separation of a mixture of liquids.
It works when liquids have different boiling points. The apparatus is similar to the one of simple distillation apparatus, with the
additional fractionating column placed on top of the heated flask.
The fractionating column contains glass beads. It helps to separate the compounds.
In industry, mixtures are repeatedly condensed and vapourised. The column is hot at
the bottom and cold at the top. The liquids will condense at different heights of the column.
Describe and explain
filtration
Filtration is used to separate an insoluble solid is suspended in a liquid.
The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper.
The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel.
Describe and explain
chromatography
Chromatography is used to separate a mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with the solvent. The solvent level will slowly start to rise, thus separating the spot (mixture) into a few spots (components).
What is a separating funnel?
A separatory funnel is an apparatus for separating immiscible liquids.
Two immiscible liquids of different densities will form two distinct layers in the separatory funnel. We can run off the bottom layer (the liquid with greater density) to a
separate vessel.
