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chemistry > separation techniques > Flashcards

separation techniques Flashcards

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1
Q

what is a pure substance

A

a pure substance is made up of only one single element/compound

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2
Q

methods to separate solid from liquid

A
  1. filtration
  2. evaporation to dryness
  3. crystallisation
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3
Q

what is filtration

A

filtration is to separate insoluble solid particles from a liquid

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4
Q

filtration

how is the solid particles collected?

A

its solid particles are larger than the pores of the filter paper and it is unable to pass through it and hence it is collected as a residue.

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5
Q

examples for filtration

A

sand and water
chalk and water
clay and water

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6
Q

what is evaporation to dryness

A

it is a process to obtain soluble solid from heating the solution until all water has been boiled off

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7
Q

limitations of evaporation to dryness

A
  1. substances that decomposes upon strong heating is not suitable for this method
  2. solid obtained may not always be pure as there are impurities left that sticks onto the solid
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8
Q

examples of evaporation to dryness

A

salt and water

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9
Q

crystallisation

A

crystallisation is to obtain pure solid from its solution

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10
Q

advantages of crystallisation

A

substances that decomposes upon strong heating can use crystallisation as it does not require strong heating

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11
Q

examples of crystallisation

A

sugar and water

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12
Q

process of boiling when crystallising

A

the solution is boiled until it forms a saturated solution

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13
Q

what happens to crystals when it is cooling

A

the hot, saturated solution cools and it appears as crystals

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14
Q

how to obtain pure crystals after cooling and boiling

A

use filtration to obtain residue and wash the solid with cold distilled water and dry it by pressing it between pieces of filter paper

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15
Q

why use cold distilled water for crystals

A

cold : avoid crystal from dissolving
distilled : remove remaining solution that sticks on the crystal

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16
Q

how to separate liquid from solution?

A

simple distillation

17
Q

what is simple distillation

A

separate pure solvent to form a solution

18
Q

example of simple distillation

A

sea water, sugar solution

19
Q

how does simple distillation work

A

solution is boiled and the liquid with the lower bp boils first into vapour and reaches the top of the flask, it then enters the condenser and gets condensed by the condenser. it is then collected as a filtrate in the flask.

20
Q

why must the thermometer be beside the condenser

A

to measure the bp of the liquid being distillated

21
Q

what are boiling chips for

A

ensure smooth boiling

22
Q

why must the condenser have water coming in from the bottom and leaving at the top>

A

this is to ensure that the water jacket is completely filled and it is to provide a more efficient cooling system

23
Q

simple distillation

what happens if the filtrate collected is volatile?

A

place conical flask on ice so that distillate remains in liquid state

24
Q

how to separate liquids

A

fractional distillation

25
Q

what is fractional distillation

A

separate a mixture of miscible liquids based on difference in boiling points

26
Q

examples of fractional distillation

A

ethanol and water

27
Q

what is the fractionating column purpose?

A

ensure that the liquid being distilled is not distilled together with the liquid of higher bp

28
Q

what is chromatography

A

separate 2 or more components that dissolve in the same solvent

29
Q

example of chromatography

A

separating inks, food dyes

30
Q

why should the colour spot be above the water

A

to prevent the colour spot from dissolving into the water and so that it can move up the paper

31
Q

principle of chromatography

A

the more soluble, the further and faster the spot goes up the paper

32
Q

importance of purity

A

to ensure that food containing chemicals are safe for consumption

33
Q

how to check impurities of solids and liquids

A

solids : check mp
liquid : check bp

chemistry (7 decks)

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