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
