Notesale: Turn your study into money

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States of matter
Depend on forces between particles
Solid
Strong forces of attraction – hold them in fixed position: regular lattice
arrangement
Have definite shape/volume
Not much energy
Can only vibrate about fixed position – slightly expand when heated
Liquid
Some force of attraction – free to move past eachother
Flow to fill bottom of container
Definite volume (not shape)
More energy than solid
Constantly moving – faster when hotter (slightly expand when heated)
Gas
No force of attraction – free to move (travel in straight lines)
No definite shape/volume
Move to fill container
Exert pressure on walls
Most energy
Constantly moving in random motion – expand / increase pressure when heated
Melt
Solid heated – particles gain energy – vibrate more – weakens forces – expands
Reaches melting point: particles have enough energy to break free from positions
Evaporate
Liquid heated – particles gain energy – move faster – weakens bonds
Reaches boiling point: particles have enough energy to break their bonds
Condense
As gas cools: particles no longer have enough energy to overcome forces of
attraction – bonds form between particles
Reaches boiling point: enough bonds have formed to become liquid
Freeze
As liquid cools: particles have less energy – move around less – not enough energy
to overcome attraction between particles – more bonds form between them
Reaches melting point: so many bonds have formed – particles held in place
Sublimate: solid to gas

Methods of separating and purifying substances
Pure:

made entirely of one element/compound
sharp melting point
Impure substance/mixture: melts over range of temperatures

Simple distillation: separate liquid from solutions – different boiling points
Distillation flask – thermometer & bung
Condenser (cold water running through)
Fractional distillation: separate mixture of liquids with similar boiling points
Distillation flask – fractioning column (cooler at top) – condenser
Collect liquids 1 at a time then change temperature
Filtration: Insoluble solid from liquid
Filter paper + funnel – holds solid residue
Crystallisation: Soluble solid from solution
Evaporating dish & heat until point of crystallisation – then cool
Paper-chromatography: soluble substance mixture
Mobile phase: where molecules can move – solvent

Stationary phase: where molecules can’t move – filter
paper
Components separate while mobile phase moves over stationary phase
Components of mixture dissolve in water and move up paper – depending on solubility in solvent
Base line in pencil – insoluble: won’t move (ink would)
Filter paper dipped into solvent: so mixtures don’t spread directly into solvent
Watch glass over top: stop solvent evaporating away
Solvent front in pencil: where solvent reaches
Pure: 1 spot – won’t separate
Rf value: ratio of distance travelled by substance
– between base line and solvent front
solvent
controlled by amount of time molecules spend in each phase
depends on:
their solubility in solvent
attraction to stationary phase
identify substances by comparing to known substances
Core Practical: Investigate ink compositions with simple distillation & paper chromatography
Water treatment
From Waste/ground-water
Water treatment plants
Filtration
Screening using grids: filters large objects
Sand/gravel bed filter: filter larger insoluble particles
Sedimentation
Iron/aluminium sulphate added to water – makes fine particles clump and settle at bottom
Chlorination
Chlorine gas bubbled through – kills harmful bacteria + other microbes
Distilling sea water
Used in dry countries
Expensive – needs lots of energy
Pure water needed for chemical analysis
Water must be deionised – removed ions that are present in tap water (calcium/iron/copper)
Could interfere with reactions – false result



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