separation techniques Flashcards
what is a pure substance
a pure substance is made up of only one single element/compound
methods to separate solid from liquid
- filtration
- evaporation to dryness
- crystallisation
what is filtration
filtration is to separate insoluble solid particles from a liquid
filtration
how is the solid particles collected?
its solid particles are larger than the pores of the filter paper and it is unable to pass through it and hence it is collected as a residue.
examples for filtration
sand and water
chalk and water
clay and water
what is evaporation to dryness
it is a process to obtain soluble solid from heating the solution until all water has been boiled off
limitations of evaporation to dryness
- substances that decomposes upon strong heating is not suitable for this method
- solid obtained may not always be pure as there are impurities left that sticks onto the solid
examples of evaporation to dryness
salt and water
crystallisation
crystallisation is to obtain pure solid from its solution
advantages of crystallisation
substances that decomposes upon strong heating can use crystallisation as it does not require strong heating
examples of crystallisation
sugar and water
process of boiling when crystallising
the solution is boiled until it forms a saturated solution
what happens to crystals when it is cooling
the hot, saturated solution cools and it appears as crystals
how to obtain pure crystals after cooling and boiling
use filtration to obtain residue and wash the solid with cold distilled water and dry it by pressing it between pieces of filter paper
why use cold distilled water for crystals
cold : avoid crystal from dissolving
distilled : remove remaining solution that sticks on the crystal
how to separate liquid from solution?
simple distillation
what is simple distillation
separate pure solvent to form a solution
example of simple distillation
sea water, sugar solution
how does simple distillation work
solution is boiled and the liquid with the lower bp boils first into vapour and reaches the top of the flask, it then enters the condenser and gets condensed by the condenser. it is then collected as a filtrate in the flask.
why must the thermometer be beside the condenser
to measure the bp of the liquid being distillated
what are boiling chips for
ensure smooth boiling
why must the condenser have water coming in from the bottom and leaving at the top>
this is to ensure that the water jacket is completely filled and it is to provide a more efficient cooling system
simple distillation
what happens if the filtrate collected is volatile?
place conical flask on ice so that distillate remains in liquid state
how to separate liquids
fractional distillation
what is fractional distillation
separate a mixture of miscible liquids based on difference in boiling points
examples of fractional distillation
ethanol and water
what is the fractionating column purpose?
ensure that the liquid being distilled is not distilled together with the liquid of higher bp
what is chromatography
separate 2 or more components that dissolve in the same solvent
example of chromatography
separating inks, food dyes
why should the colour spot be above the water
to prevent the colour spot from dissolving into the water and so that it can move up the paper
principle of chromatography
the more soluble, the further and faster the spot goes up the paper
importance of purity
to ensure that food containing chemicals are safe for consumption
how to check impurities of solids and liquids
solids : check mp
liquid : check bp
