C2 - purification and seperation techniques Flashcards
what is a pure substance?
a substance that contains of only one element or compound
what is a mixture?
a substance containing more than 1 compound or different elements no part of the same compound, not chemically joined together
what is an element
one type of atom
what is a compound
2 or more types of atom bonded together
melting point of pure substances
sharp melting point
eg. pure water will boil at 100°c exactly
how can the purity of a sample be tested
comparing the melting point of a sample to the expected value
melting point of a mixture/ impure substance
gradually over a range of temperatures
what are the 2 types of distillation
simple and frational
what is simple distillation used for
separating a liquid(solvent) from a solution
how does simple distillation work
- solution is put into a flask
- run cold water through condenser to keep it cool
- flask is gradually heated until the solution evapourates(bp is much lower than solute)
- vapour passes through condenser where it cools and becomes a liquid again
- liquid is collected in a beaker
- solute remains in flask
problem with simple distillation
only used to separate things with very different boiling points
example of substances that can be separated with simple distillation
pure water from saltwater/ sea water
what is frational distillation used for
separating a mixture of liquids
how does frational distillation work
- mixture put in flask attached to fractionating column attached to condenser
- flask is heated, liquid with lowest bp evapourates first
- when temp on thermometer reaches bp of liquid, it reaches the top then returns to liquid in condenser and collected
why won’t other liquids also reach the condenser in fractional distillation
top of fractionating column is cooler than bottom so other liquids even if they begin to evapourate, wont reach the top before condensing and running back down the column
examples of when fractional distillation is used
to separate different hydrocarbons from crude oil
what is filtration used for
separating insoluable solid from liquid
how does filtration work
filter paper has tiny holes allowing small molecules and dissolved ions through but not larger molecules of insoluable solid
steps of filtration
- mixture of solid and liquid poured into filter funnel (funnel with filterpaper in)
- liquid drips through solid is caught in paper
examples of mixtures separated by filtration
- sand from sandy water
- excess reactant from a solution (copper oxide)
what is crystallisation used for
- separating a soluable solid from a solution
steps of crystallisation
- solution is poured into an evapourating dish and heated
- water will begin to evaporate
- once crystals begin to form dish removed from heat
- pour excess liquid away
- allow crystals to dry
problems with crystallisation
liquid is not collected (simple distillation should be used if liquid is to be collected)
what substances can be separated by crystallisation
salt and water
