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IGCSE Chemistry > 4.6 - Chemical Analysis > Flashcards

4.6 - Chemical Analysis Flashcards

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1
Q

simple distillation

A

This method is used to separate a liquid from a solution

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2
Q

example of simple distillation

A

E.g. separating water from salt water:
The salt water is boiled. The water vapour condenses back into a liquid when passed through the condenser. The salt is left behind in the flask.

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3
Q

fractional distillation

A

This method is used to separate a mixture of different liquids that have different boiling points

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4
Q

example of fractional distillation

A

E.g. separating alcohol from a mixture of alcohol and water:
Water boils at 100C and alcohol boils at 78C -> only the alcohol remains as vapour all the way up to the top of the column and passes into the condenser.

The alcohol vapours then condense back into a liquid.

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5
Q

filtration

A

This method is used to separate an insoluble solid from a liquid

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6
Q

example of filtration

A

E.g. separating sand from a mixture of sand and water:
The mixture is poured into the filter paper. The sand does not pass through and is left behind (residue) but the water passes through the filter paper and is collected in the conical flask (filtrate).

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7
Q

residue in filtration

A

the solid left behind

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8
Q

filtrate

A

the solution collected in conical flask

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9
Q

crystallisation

A

This method is used to obtain a salt which contains water of crystallisation from a salt solution

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10
Q

example of crystallisation

A

For example: hydrated copper sulfate crystals (CuSO4.5H2O(s)) from copper sulfate solution (CuSO4(aq)).

  • Gently heat the solution in an evaporating basin to evaporate some of the water
    until crystals form on a glass rod (which shows that a hot saturated solution has formed).
  • Leave to cool and crystallise.
  • Filter to remove the crystals.
  • Dry by leaving in a warm place.
  • If instead the solution is heated until all the water evaporates, you would produce a powder of anhydrous copper sulfate (CuSO4(s)).
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11
Q

paper chromatography

A

This method can be used to separate the parts of a mixture into their components. E.g. the different dyes in ink can all be separated and identified

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12
Q

example of paper chromatography

A

The coloured mixture to be separated (e.g. a food dye) is dissolved in a solvent like water or ethanol and carefully spotted onto the chromatography paper on the baseline, which is drawn in pencil so it doesn’t ‘run or smudge’.

  • The paper is carefully dipped into the solvent
  • The solvent is absorbed into the paper and rises up it as it soaks into the paper.
  • As the solvent rises up the paper it will carry the dyes with it.
  • Each different dye will move up the paper at different rates depending on how strongly they stick to the paper and how soluble they are in the solvent.
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13
Q

If the dye does not dissolve in water (paper chromotography)

A

it is an organic solvent
(e.g. ethanol)

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14
Q

How can paper chromatography can be used to investigate the composition of a mixture

A
  • A baseline is drawn on the paper
  • The mixture is spotted onto the baseline alongside known or standard reference materials.
  • The end of the paper is then put into a solvent which runs up the paper and through the spots, taking some or all of the dyes with it.
  • Different dyes will travel different heights up the paper.
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15
Q

calculation of Rf values to identify the components of a mixture

A

The distance of dye
____________________________________
distance solvent travelled from the baseline

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16
Q

investigate paper chromatography using inks/food colourings

A
  • A pencil line (baseline) is drawn 1cm from the bottom of the paper. Pencil will not dissolve in the solvent, but if ink were used instead it might dissolve and interfere with the results of the chromatography.
  • A spot of each sample of dye is dropped at different points along the baseline.
  • Paper is put in a beaker which contains a small amount of solvent.
  • The bottom of the paper should be touching the solvent, but the baseline with the dyes should be above the level of the solvent. This is important so the dyes don’t simply dissolve into the solvent in the beaker.
  • When the solvent has travelled to near the top of the paper, the paper is removed from the solvent and a pencil line drawn (and labelled) to show the level the solvent reached up the paper. This is called the solvent front.
  • The chromatogram is then left to dry so that all the solvent evaporates.
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17
Q

test for hydrogen gas

A

squeaky pop test with lit splint when H2 present

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18
Q

test for oxygen

A

glowing splint relights when O2 present

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19
Q

test for carbon dioxide

A

bubbling the gas through limewater turns cloudy

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20
Q

test for ammonia

A

damp red litmus paper turns blue in presence of NH3

21
Q

test for chlorine

A

blue damp litmus paper turns white –> bleaches

22
Q

combustion of H2 equation

A

2H2(g) + O2(g) -> 2H2O(g)

23
Q

test for purity of H2O

A

measure boiling point and compare to 100C

24
Q

forming of calcium carbonate when it reacts which carbon dioxide

A

Ca(OH)2(aq) + CO2(g) -> CaCO3 + H2O

25
Q

when ammonia reacts which dampness to form OH- ions

A

NH3(g) + H2O(l) => NH4(aq) + OH-(aq)

26
Q

how to carry out flame test

A

Platinum/nichrome wire is dipped into hydrochloric acid to remove any impurities.
The wire is dipped into the salt being tested so some salt sticks to the end.
The wire and salt are held in a roaring bunsen burner flame.
The colour is observed.

27
Q

what does flame tests show

A

presence of certain metal ions (cations) in a compound

28
Q

flame tests: Li+

A

red

29
Q

flame tests: Na+

A

yellow

30
Q

flame tests: K+

A

lilac

31
Q

flame tests: Ca2+

A

orange-red

32
Q

flame tests: Cu2+

A

blue-green

33
Q

cation tests: copper (III) ions
(Cu2+)

A

effect of adding sodium hydroxide (NaOh):
Light blue precipitate formed

34
Q

cation tests: iron (II) ion
(Fe2+)

A

effect of adding sodium hydroxide (NaOh):
Green precipitate formed

35
Q

cation tests: iron (III) ion
(Fe3+)

A

effect of adding sodium hydroxide (NaOh):
Brown precipitate formed

36
Q

cation tests: ammonium ion
(NH4+)

A

effect of adding sodium hydroxide (NaOh):
Ammonia gas is produced which turns damp red litmus paper blue

37
Q

cation/sodium hydroxide tests: fully balanced equation

A

__Cl2(aq) + 2NaOH(aq) –> __(OH)2(s) + 2NaCl(aq)

38
Q

cation/sodium hydroxide tests: ionic equation that shows formation of precipitate

A

__(aq) + 2OH-(aq) –> __(OH)2 (s)

39
Q

presence of water

A

Add anhydrous copper (II) sulfate (CuSO4) to a sample
white –> blue

40
Q

describe a physical test to show whether a sample of water is pure

A

if the sample is pure water it will boil at 100C

41
Q

ammonia reacts with NaOH(aq) forming NH3(g)

A

damp red litmus paper
- turns blue
- shows pre scene of ammonia gas

42
Q

copper (II) produces

A

blue precipitate

43
Q

iron (II) produces

A

green precipitate

44
Q

iron(III) produces

A

brown precipitate

45
Q

halide ions experiments bromide and iodide

A
  • add dilute nitric acid followed by silver nitrate solution

bromide - cream precipitate
iodide - yellow precipitate

46
Q

sulfate ions

A
  • add dilute hydrochloric acid followed by barium chloride solution
  • white precipitate formed when sulphate ions present
47
Q

carbonate ions

A
  • gas bubbled through limewater and goes cloudy
48
Q

fractional distillation crude oil separation

A
  • crude oil vaporised
  • vapour rises up column
  • hotter at bottom and colder at top
  • condenses at diff levels depending on boiling point

IGCSE Chemistry (13 decks)

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