States of Matter and seperating mixtures Flashcards
Turning a gas to a solid is called
Deposition
Turning a solid to a gas is called
Sublimation
Explain the changes in arrangement, movement and energy of particles during these interconversions (solid to liquid, liquid to gas etc)
Melting: When a solid is heated, the energy makes the particles vibrate fast enough so that the forces of attraction between the particles break.
Freezing: When a liquid is cooled, the particles move slow enough so that the forces of attraction between them will hold them into a solid.
Boiling: When a liquid is heated strongly, the energy makes the particles move fast enough so that all forces of attraction are broken.
Condensing: When a gas is cooled, the particles move slow enough so that the forces of attraction between them will hold them as a liquid.
Whats the difference between a pure substance and a mixture
A pure substance has a fixed melting and boiling point, while a mixture, containing two or more substances, melts and boils over a range of temperatures.
A pure substance contains one type of element/compound while a mixture contains 2 or more substances which are physically combined but not chemical bonded
Explain simple distillation
Simple distillation:
o Simple distillation is used to separate a solvent from a solution. It is useful for producing water from salt solution.
▪ Simple distillation works because the dissolved solute has a much higher boiling point than the solvent
▪ When the solution is heated, solvent vapour evaporates from the solution. The gas moves away and is cooled and condensed.
▪ The remaining solution becomes more concentrated in solute as the amount of solvent in it decreases.
Explain fractional distillation
Fractional distillation:
o Used to separate a pure liquid from a mixture of liquids
▪ Works when the liquids have different boiling points
▪ Commonly used to separate ethanol from water
▪ (Taking the example of ethanol…) ethanol has a lower bp than water so it evaporates first. The ethanol vapour is then cooled and condensed inside the condenser to form a pure liquid.
▪ Sequence of events in distillation is as follows: heating -> evaporating -> cooling -> condensing
Explain filtration
Filtration:
o If you have produced e.g. a precipitate (which is an insoluble salt), you would want to separate the salt/precipitate from the salt solution.
▪ You would do this by filtering the solution, leaving behind the precipitate on the filter paper
Explain crystallisation
Crystallisation:
o If you were to have produced a soluble salt and you wanted to separate this salt from the solution that it was dissolved in
▪ You would first warm the solution in an open container, allowing
the solvent to evaporate, leaving a saturated solution
▪ Allow this solution to cool
▪ The solid will come out of the solution and crystals will start to
grow, these can then be collected and allowed to dry
Explain paper chromatography
Paper chromatography:
▪ Used to separate mixtures and give information to help identify substances
▪ Involves a stationary phase and a mobile phase
▪ Separation depends on the distribution of substances between the phases
The higher a substance has moved up, the more soluble it is
How do we calculate the Rf value
Rf value = distance moved by substance / distance moved by solvent
Solvent front (chromatography)
Distance moved by solvent
Solvent
Liquid which a solute dissolves in to form a solution
Baseline (chromatography)
Starting position of sample
Why does each sample need to be far (chromatography)
so they dont mix
Why is the baseline drawn in pencil (chromatography)
otherwise pen would mix in with the inks
Describe paper chromatography as the separation of mixtures of ______ _______ by running a ______ (mobile phase) through the mixture on the ________ (the ______ contains the stationary phase), which causes the…
soluble substances
solvent
paper
paper
substances to move at different rates over the paper
Interpret a paper chromatogram: to distinguish between pure and impure substances, to identify substances by comparison with known substances
● pure substances: should only have one spot on a chromatogram
● impure substances/mixtures: will show up with more than one spot on a chromatogram
● to identify by comparing with known substances: carry out paper chromatography with both the known substance and substance you’re testing on the same paper. If both spots are at the same height up the paper at the end then you know the substance you’re testing is the same as the known substance.
