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chemical analysis Flashcards

1
Q

in chemistry, what is a pure substance

A

a substance made up of a single element or compound, not mixed with any other substances

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2
Q

in everyday language, what is a pure substance

A

a substance that has nothing added to it, in its natural state

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3
Q

boiling & melting points for pure substances are…

A

at a fixed temperature, eg pure water would only be boiled at 100’C

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4
Q

boiling & melting points for impure substances are…

A

over a range, eg salty water would boil from 100-105’C

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5
Q

formulation

A

mixture that has been designed as a useful product

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6
Q

how are formulations made

A

by mixing components in carefully measured quantities to get the required properties

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7
Q

formulation examples

A
  • fuel
  • cleaning agent
  • paint
  • medicine
  • alloys
  • fertilisers
  • food
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8
Q

method to separate dyes

A

chromatography

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9
Q

phases of chromatography

A

stationary & mobile phase

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10
Q

what is the stationary phase

A

the chromatography paper

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11
Q

what is the mobile phase

A

the solvent (usually water)

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12
Q

what must you use to draw the line for chromatography and why

A

pencil
this is insoluble in the solvent so it will not run

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13
Q

where must the water be in relation to the pencil line

A

water line must be below the pencil line to stop inks mixing with the solvent

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14
Q

what does the distance the dots move tell you

A

how soluble the ink is in the solvent - if it moves to the top it is very soluble

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15
Q

if the dot doesnt move off the pencil line what does that tell you?

A

the ink is insoluble in the solvent

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16
Q

explain how the inks are separated using paper chromatography

A

inks have different solubilities. this means they move up the paper at different speeds/distances

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17
Q

what is Rf value

A

the ratio of the distance moved by a compound to the distance moved by the solvent

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18
Q

how can you express Rf

A

Rf = distance dot travelled / distance solvent travelled

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19
Q

how do we use Rf values?

A

theyre used to identify substances. each substance has a specific Rf value so we use these to confirm what is in a mixture

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20
Q

what value is Rf alway below

A

1

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21
Q

how many spots would you get for a pure substance

A

one

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22
Q

how many spots would you get for a mixture

A

more than one

23
Q

test for hydrogen

A

burning splint
makes a squeaky pop noise

24
Q

test for oxygen

A

glowing splint
splint relights

25
test for carbon dioxide
bubble through limewater limewater turns milky/cloudy
26
test for chlorine
damp blue litmus paper turns bleached white
27
test for ions which produces colour when burnt
flame tests
28
what can you test with a flame test
- lithium - sodium - potasium - calcium - copper
29
flame test - lithium
crimson red
30
flame test - sodium
yellow
31
flame test - potassium
lilac
32
flame test - calcium
orange-red
33
flame test - copper
green
34
what should you do if identifying ions in a tablet
crush into a powder or dissolve in water
35
what happens if there is a mixture of ions in a sample
some flame colours can be masked
36
hydroxide to identify some metal ions in a solution
sodium hydroxide
37
what can you test with sodium hydroxide
- aluminium - magnesium - calcium - iron (II) - iron (III) - copper (II)
38
s.h - aluminium, calcium, magnesium
white precipitate
39
s.h - copper (II)
blue precipitate
40
s.h - iron (II)
green precipitate
41
s.h - iron (III)
brown precipitate
42
how can you distinguish between aluminium magnesium and calcium
add excess sodium hydroxide aluminium hydroxide precipitate will dissolve
43
half equation to show formulation of the blue precipitate between copper (II) and sodium hydroxide
Cu2+ 2OH --> Cu(OH)2
44
test for carbonate
react with a dilute acid forms carbon dioxide gas identified using limewater, goes cloudy
45
test for halide
silver nitrate solution presence of dilute nitric acid precipitates form
46
chloride & silver nitrate
white precipitate
47
bromide & silver nitrate
cream precipitate
48
iodide & silver nitrate
yellow precipitate
49
test for sulphate
barium chloride in presence of dilute hydrochloric acid
50
sulphate & barium chloride
white precipitate
51
advantages of instrumental methods
- accurate - more sensitive - rapid - ease of use - reliable / efficient - sample doesnt get used up
52
instrumental method to detect metal ions in solution
flame emission spectroscopy
53
how is flame emission spectroscopy carried out
sample is put in a flame light given out is passed through a spectroscope the output is a line spectrum

chem paper 2 (3 decks)

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