Separating and purifying Flashcards
(28 cards)
What are the 3 states of matter
- solid
- liquid
- gas
What are state changes?
Physical changes, they can be reversed
What is is called when a substance goes form a solid to a gas?
Sublimation
What is it called when you go from a gas to a solid?
Deposition
What attracts particle together?
Weak forces of attraction
What needs to happen to overcome weak forces of attraction during evaporation?
Energy must be transferred from the surroundings to the particles
What needs to happen for attractive forces to form during freezing?
Energy must be transferred from the particles to the surroundings
The composition (make-up) of a pure substance:
- cannot be changed
- is the same in all parts of a piece of substance
Why can’t we use physical methods to separate pure substances?
It is in the same fixed composition in all its parts
What is a mixture?
Elements and/or compounds that are not chemically joined together
Do mixtures have fixed compositions?
No
What happens when something melts?
The particles gain enough energy to overcome weak forces of. They move further and further away from each other and the solid becomes a liquid
What temperature does a pure substance melt over?
The same temperature until the substance has changed state
What is a solution?
A mixture made of solutes in a liquid called the solvent
What is crystallisation?
Evaporating a substance to leave the solutes behind
What does it mean if the crystals form slowly?
Particles have longer to form an ordered pattern and will make larger crystals
How can risks in crystallisation be reduced?
-risks of spitting are reduced by :
wearing safety goggles
Removing the Bunsen burner before solution is completely dry
Use steam to evaporate the basin
What can chromatography be used for?
To find out which coloured compounds the mixture contains
How do you work out the Rf value?
Rf=distance moved by spot/distance moved by solvent
What can paper chromatography be used for?
- distinguish between pure and impure substances
- identify substances by comparing the pattern on the chromatogram with the patterns formed by known substances
- identifying substances by calculating there Rf values
What is the combination of evaporation followed by condensation?
Distillation
What is the apparatus used in distillation called?
Still
What can fractional distillation be used for?
- separate different products in crude oil
- make alcoholic drinks such as whisky and vodka
- separate put the gases in the air after air has been cooled and turned into a liquid
What is desalination?
Producing pure water from sea water
