Chemistry Separation Techniques Flashcards
What is an element?
A substance made up of only one type of atom
What is a mixture?
Substance made up of 2 or more types of atoms not chemically joined together
What is a compound?
Substance made up of 2 or more types of atoms chemically joined
together
How can we tell if something is pure?
Pure substances melt and boil at specific and sharp temperatures e.g. pure water has a
boiling point of 100 °C and a melting point of 0 °C. Mixtures have a range of melting and
boiling points as they consist of different substances that tend to lower the melting point
and broaden the melting point range. Melting and boiling points data can therefore be
used to distinguish pure substances from mixtures
What is filtration used for
Used to separate an insoluble solid from a mixture of the solid and a liquid / solution
Eg. Sand and salt
What is distillation used for?
To separate a liquid and soluble solid from a solution or a pure liquid from a mixture of liquids
Eg. water from a solution of salt
and water
What is crystallisation used for?
It is used to separate a soluble solid from a liquid.
Eg. Salt from a solution of salt and water
What is chromatography used for?
To separate soluble substances that have different solubilities in a solvent
How does distillation work?
A Liebig condenser is used or a delivery tube with ice.
The solution is heated to evaporate the liquid.
The gas travels down the condenser, where it is cooled, so it condenses back into a liquid.
The liquid is collected in the beaker and the soluble solid remains in the flask.
How does filtration work?
Filtration is used to separate an insoluble solid from a mixture of the solid and a liquid /
solution
piece of filter paper is placed in a filter funnel above a conical flask
mixture of insoluble solid and liquid is poured into the filter funnel
filter paper only allows the liquid and dissolved solid through. The solution that passes
through the filter paper is known as the filtrate
insoluble solid particles are too large to pass through the filter paper. This is known as the
residue
How does crystallisation work?
Crystallisation is used to separate a soluble solid from a liquid
The solution is heated to partially evaporate the liquid to form a saturated solution
Heated to the
point of crystallisation
the saturated solution is then allowed to cool slowly so as to allow crystals to form
crystals are filtered
crystals are dried (in an oven) to remove any excess water
How does chromatography work?
Chromatography is used to identify a substance and/or separate soluble substances that
have different solubilities in a solvent
a pencil line is drawn near the bottom of chromatography paper
the line is drawn in pencil as it is insoluble
place the control sample / samples to be tested on the pencil line
paper is then placed in solvent (usually water)
The samples must be above the solvent otherwise they will just dissolve in the solvent.
the solvent travels up the chromatography paper by capillary action
soluble substances will travel with the solvent with those that are more soluble being able
to travel further up the chromatography paper. This is called a chromatogram
If two or more substances are the same, they will produce the same chromatogram
What is the calculation for RF values?
Rf value = Distance moved by substance / distance moved by solvent
