separation techniques Flashcards
how do you decide what separation method to use
depending on whether the solid is dissolved, and how its solubility changes with temperature.
what is the name of the insoluble solid
residue
what is the name of the soluble liquid
flitrate
why does crystallisation work
because soluble solids tend to be less soluble at lower temperatures.
name the steps of crystallisation in order
- heat the solution to evaporate some water so that it is more concentrated
- eventually the solution will become saturated. when it cools, crystals will start to form
- check that it’s ready by placing a drop on a microscope slide, crystals will form quickly on the cool glass.
- leave the solution to cool, crystals will start to form in it as the temperature falls.
- remove crystals by filtration. rinse with distilled water and dry with filter paper.
why doesn’t crystallisation always work
because some substances, the solubility changes very little as the temperature falls.
define solvent
the dissolving medium (liquid)
define solute
the substance being dissolved in (solid)
how does ‘evaporating all the solvent’ work
- keep heating solution to evaporate the solvent
- when there is only a little solvent left, the solute will start to appear. heat carefully until dry.
how do you separate a mixture of two solids
choose a solvent that will dissolve into only one of them
name the steps of ‘separating a mixture of two solids’ in order
- add a solvent to the mixture that would dissolve one of the solutes and stir. The solute dissolves.
- filter the mixture. the second solute is trapped in the filter paper, but the first solute solution passes through.
- rinse the second solute with water, and dry it in an oven.
- evaporate the solvent from the first solute solution, to give a dry solute.
if a solvent is flammable, how do you evaporate it
using a water bath
define filtrate
the liquid that passed through a filter paper
define simple distillation
a way to obtain the solvent from a solution.
name the steps of simple distillation in order
- heat the solution in the flask. as it boils, water vapour rises into the condenser, leaving salt behind.
- the condenser is cold, so the vapour condenses to water in it.
- the water drips into the beaker. (it is called distilled water. It is almost pure)
where do people commonly use simple distillation, and for what reason
the middle east, many obtain drinking water through simple distillation by distilling seawater in giant distillation plants.
define residue
the trapped solid in a filter paper
define fractional distillation
used to separate a mixture of liquids from each other.
what factor does fractional distillation rely on
the different boiling points
name the steps of frational distillation in order
- heat the mixture in the flask. at a certain temperature, the first solute begins to boil. some of the second solute evaporates too. so a mixture of the two solutes vapours rises up the column.
- the vapours condense on the glass beads in the column, making the beads hot.
- when the beads reach the boiling point of the first solute, the solute’s vapour no longer condenses on them. only the second solute’s vapour does. so the first solute drips back into the flask. the second solute vapour goes into the condenser.
- there it condenses. pure liquid of solute one drips into the beaker. eventually, the thermometer reading rises above the boiling point of solute one – a sign that all the ethanol has gone. so you can stop heating.
what industry commonly uses fractional distillation and what do they use it for
the petroleum industry, to refine crude oil into petrol and other groups of compounds.
how does paper chromatography work
dyes in the ink have different solubilities in water. so they travel across the paper at different rates. (The most soluble one travels fastest.)
what is a chromatogram
the result of paper chromatography
how does the solubility of a solute affect the chromatography results
the more soluble a substance is in the solvent, the further it will travel up the chromatography paper.
what is the formula for the Rf value
distance moved by amino acid/distance moved by solvent
what are the different uses for paper chromatography
- identify a substance
- separate mixtures of substances
- purify a substance, by separating it from its impurities.
define ‘locating agent’
a solution used to locate the position of a colourless solution
why does the Rf table method work
method works because the Rf value of a compound is always the same for a given solvent, under the same conditions.
define ‘saturation’
the condition in which one substance takes up as much space as possible within another substance and it can take no more molecules
