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GCSE - chemistry > C2 - purification and seperation techniques > Flashcards

C2 - purification and seperation techniques Flashcards

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1
Q

what is a pure substance?

A

a substance that contains of only one element or compound

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2
Q

what is a mixture?

A

a substance containing more than 1 compound or different elements no part of the same compound, not chemically joined together

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3
Q

what is an element

A

one type of atom

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4
Q

what is a compound

A

2 or more types of atom bonded together

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5
Q

melting point of pure substances

A

sharp melting point

eg. pure water will boil at 100°c exactly

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6
Q

how can the purity of a sample be tested

A

comparing the melting point of a sample to the expected value

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7
Q

melting point of a mixture/ impure substance

A

gradually over a range of temperatures

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8
Q

what are the 2 types of distillation

A

simple and frational

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9
Q

what is simple distillation used for

A

separating a liquid(solvent) from a solution

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10
Q

how does simple distillation work

A
  • 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
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11
Q

problem with simple distillation

A

only used to separate things with very different boiling points

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12
Q

example of substances that can be separated with simple distillation

A

pure water from saltwater/ sea water

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13
Q

what is frational distillation used for

A

separating a mixture of liquids

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14
Q

how does frational distillation work

A
  • 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
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15
Q

why won’t other liquids also reach the condenser in fractional distillation

A

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

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16
Q

examples of when fractional distillation is used

A

to separate different hydrocarbons from crude oil

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17
Q

what is filtration used for

A

separating insoluable solid from liquid

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18
Q

how does filtration work

A

filter paper has tiny holes allowing small molecules and dissolved ions through but not larger molecules of insoluable solid

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19
Q

steps of filtration

A
  • mixture of solid and liquid poured into filter funnel (funnel with filterpaper in)
  • liquid drips through solid is caught in paper
20
Q

examples of mixtures separated by filtration

A
  • sand from sandy water
  • excess reactant from a solution (copper oxide)
21
Q

what is crystallisation used for

A
  • separating a soluable solid from a solution
22
Q

steps of crystallisation

A
  • 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
23
Q

problems with crystallisation

A

liquid is not collected (simple distillation should be used if liquid is to be collected)

24
Q

what substances can be separated by crystallisation

A

salt and water

25
Q

what is chromatography used for

A

separate a mixture of soluable substances and identify them

26
Q

what are the 2 phases of chromatography

A

mobile phase

stationary phase

27
Q

what is a mobile phase

A

molecules can move. always liquid or gas

28
Q

what is a stationary phase

A

molecules cant move. solid or thick liquid

29
Q

what is the stationary phase in paper chromatography

A

filter paper

30
Q

what is the mobile phase in paper chromatography

A

solvent/ water

31
Q

steps of paper chromatography

A
  • line drawn in pencil near bottom of paper
  • a spot of mixture is put on line
  • bottom of paper is put in a beaker of solvent below the line
  • solvent will travel up paper and the mixture will begin to separate
  • paper removed before solvent reached top
  • solvent front marked in pencil
32
Q

why should the line be marked in pencil

A

pencil is insoluable, pen in will dissolve in the solvent

33
Q

what is a solvent front

A

how far the solvent travelled

34
Q

how can the soluability of solute be told in chromatography

A

more soluable = travel further up the paper

35
Q

what is a chromatogram

A

the piece of paper left after chromatography with all separated substances

36
Q

how can Rf value be calculated

A

distance travelled by solute/

distance travelled by solvent

37
Q

how to tell if Rf value is correct

A

has to be less than 1, solute cant travel further than solvent

38
Q

how can chromatography be a purity test

A

pure substance wont separate, will move as one blob

mixture separates into multiple blobs

39
Q

what is potable water

A

water that is safe to drink

40
Q

sources of water that is purified for potable water in UK

A

surface water: lakes, rivers
groundwater:rockstrapwaterunderground
waste water: contaminatedby humanprocess

41
Q

3 steps of water treatment

A

filtration, sedimentation, chlorination

42
Q

what is filtration

A
  • removes insoluable solids eg. twigs, stones with wire mesh

- sand beds and gravel filter any other solid bits out

43
Q

what is sedimentation

A
  • iron sulfate/ aluminium sulfate added to water making fine particle settle at bottom
44
Q

what is chlorination

A
  • chlorine gas bubbled through to kill microorganisms and sterilize water
45
Q

problems with distillation for potable water from sea water

A

used lots of energy so it is very expensive to produce large quantities

46
Q

why must pure water be used in experiments

A

potable water from taps is safe to drink but still contains ions and minerals which can interfere with reactions and give false result

47
Q

Ways to get potable water from sea water

A

Desalination:
- distillation (simple)
- reverse osmosis

GCSE - chemistry (15 decks)

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