chemical analysis Flashcards
in chemistry, what is a pure substance
a substance made up of a single element or compound, not mixed with any other substances
in everyday language, what is a pure substance
a substance that has nothing added to it, in its natural state
boiling & melting points for pure substances are…
at a fixed temperature, eg pure water would only be boiled at 100’C
boiling & melting points for impure substances are…
over a range, eg salty water would boil from 100-105’C
formulation
mixture that has been designed as a useful product
how are formulations made
by mixing components in carefully measured quantities to get the required properties
formulation examples
- fuel
- cleaning agent
- paint
- medicine
- alloys
- fertilisers
- food
method to separate dyes
chromatography
phases of chromatography
stationary & mobile phase
what is the stationary phase
the chromatography paper
what is the mobile phase
the solvent (usually water)
what must you use to draw the line for chromatography and why
pencil
this is insoluble in the solvent so it will not run
where must the water be in relation to the pencil line
water line must be below the pencil line to stop inks mixing with the solvent
what does the distance the dots move tell you
how soluble the ink is in the solvent - if it moves to the top it is very soluble
if the dot doesnt move off the pencil line what does that tell you?
the ink is insoluble in the solvent
explain how the inks are separated using paper chromatography
inks have different solubilities. this means they move up the paper at different speeds/distances
what is Rf value
the ratio of the distance moved by a compound to the distance moved by the solvent
how can you express Rf
Rf = distance dot travelled / distance solvent travelled
how do we use Rf values?
theyre used to identify substances. each substance has a specific Rf value so we use these to confirm what is in a mixture
what value is Rf alway below
1
how many spots would you get for a pure substance
one
how many spots would you get for a mixture
more than one
test for hydrogen
burning splint
makes a squeaky pop noise
test for oxygen
glowing splint
splint relights
test for carbon dioxide
bubble through limewater
limewater turns milky/cloudy
test for chlorine
damp blue litmus paper
turns bleached white
test for ions which produces colour when burnt
flame tests
what can you test with a flame test
- lithium
- sodium
- potasium
- calcium
- copper
flame test - lithium
crimson red
flame test - sodium
yellow
flame test - potassium
lilac
flame test - calcium
orange-red
flame test - copper
green
what should you do if identifying ions in a tablet
crush into a powder or dissolve in water
what happens if there is a mixture of ions in a sample
some flame colours can be masked
hydroxide to identify some metal ions in a solution
sodium hydroxide
what can you test with sodium hydroxide
- aluminium
- magnesium
- calcium
- iron (II)
- iron (III)
- copper (II)
s.h - aluminium, calcium, magnesium
white precipitate
s.h - copper (II)
blue precipitate
s.h - iron (II)
green precipitate
s.h - iron (III)
brown precipitate
how can you distinguish between aluminium magnesium and calcium
add excess sodium hydroxide
aluminium hydroxide precipitate will dissolve
half equation to show formulation of the blue precipitate between copper (II) and sodium hydroxide
Cu2+ 2OH –> Cu(OH)2
test for carbonate
react with a dilute acid
forms carbon dioxide gas
identified using limewater, goes cloudy
test for halide
silver nitrate solution
presence of dilute nitric acid
precipitates form
chloride & silver nitrate
white precipitate
bromide & silver nitrate
cream precipitate
iodide & silver nitrate
yellow precipitate
test for sulphate
barium chloride in presence of dilute hydrochloric acid
sulphate & barium chloride
white precipitate
advantages of instrumental methods
- accurate
- more sensitive
- rapid
- ease of use
- reliable / efficient
- sample doesnt get used up
instrumental method to detect metal ions in solution
flame emission spectroscopy
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
