Topic 2 - States of matter and mixtures Flashcards
Particle Model of Solids
- strong forces of attraction between particles
- close together
- regular arrangement
- vibrate on the spot
Particle Model of Liquids
- weak forces of attraction between particles
-close together
-irregular arrangement
-free to move past each other
Particle Model of Gases
- very weak forces of attraction between particles
- far apart
- irregular arrangement
- free to move past each other in random motions
Solid - Liquid
-melting
- when a solid is heated, its particles gain energy and vibrate more
- weakens the forces that hold the solid together
- at the melting point , the particles have enough energy to break free from their positions
Liquid - Gas
-boiling
- when a liquid is heated, its particles gain energy and move faster
- weakens the attractive forces that hold the liquid together
- at the boiling point , the particles have enough energy to overcome any remaining attractive forces
Gas - Liquid
- condensing
- as the gas cools, the particles no longer have enough energy to overcome forces of attraction
-below a certain temp, the forces of attraction become strong enough to convert the gas into a liquid
Liquid - Solid
- freezing
as the liquid cools, the particles no longer have enough energy to overcome forces of attraction - particles less free to move
-below melting point , the forces of attraction become strong enough to keep particles held in place in a solid
Predicting state of substance
- below melting point : solid
- in between melting &boiling point : liquid
- above boiling point : gas
Pure substance
a pure substance is completely made up of only a single element or molecule
How to test for pure substances
A chemically pure substance will have a sharp, specific melting and boiling point .
Measure melting point of substance using melting point apparatus and see if it is the same as value in data book
Simple Distillation
- separates liquid from a mixture
- water from seawater
Simple Distillation Process
- sample poured into distillation flask
- connect bottom of condenser to cold tap to keep it cool
- flask is gradually heated
-lowest BO component evaporates, vapour passes into the condenser where it condenses, - collected as a liquid in another container
fractional distillation
- separating mixture of different liquids with similar boiling points
-crude oil
fractional distillation - process
- sample poured into distillation flask
- liquid with lowest BO evaporates first, and rises up the fractionating column filled with glass rods
-it passes into the condenser and is collected back as a liquid - liquids with higher BO will start to evaporate but only get part way up the column before condensing back down, as it is cooler at the top
- once first liquid is collect, raise the temp to the boiling point of next lowest BO component
Filtration
-separate insoluble solid from mixture
- sand from water
- fold filter paper into cone and put it in a filter funnel
-put funnel on neck of a conical flask
-pour mixture through funnel into the flask, the insoluble solid will be collected
Crystallisation
-separate soluble solid from mixture
- salt from water
- place evaporating dish on top of a tripod with a gauze mat
- heat the dish using a bunsen burner
- pour solution into evaporating dish and gently heat it
- once crystals start to form, remove it from the heat and it should start to form crystals
- filter crystals out and dry in a desiccator
Mobile phase
where the molecules can move. usually a liquid or gas
Stationary phase
where the molecules can’t move. in paper chromatography it is paper.
What will a pure substance look like
a pure substance will produce a single spot in all solvents
Rf value
distance travelled by solute / distance travelled by solvent
Why do we use pencil to draw the base line?
if we drew the line in pen, the line would move up the paper with the solvent. pencil is insoluble
why does the solvent need to be below the pencil line at the start
if the ink touches the solvent initially it will be washed away
Potable water
water that is safe for humans to drink
- contains low levels of salts and microbes
sources of water
surface water
ground water
waste water
purifying water - filtration
a wire mesh screens out large twigs and sand beds filter out big objects
purifying water - sedimentation
iron sulfate is added which makes fine particles clump together
purifying water - chlorination
chlorine gas is bubbled through to kill harmful bacteria and microbes
desalination
used in dry countries where there isn’t enough surface water or ground water, so saltwater is used instead
distillation or reverse osmosis
it consumes a lot of energy and is very expensive
