Topic 8- Chemical Analysis Flashcards
(41 cards)
what is meant by a pure substance
something that only contains one compound or element throughout
how can you test the purity of a sample
by measuring its melting or boiling point and comparing it with the melting/boiling point of the pure substance (which can be found from a data book)
the closer your value is to the actual bp or mp, the purer your sample is
what do impurities do to a sample
lower the mp
increase the melting range of the substance
increase the bp
may result in your sample boiling at a range of temperatures
what is a formulation
a useful mixture with a precise purpose which is made by following a formula ‘recipe’.
example… paint
pigment solvent binder and additives are added in specific, measured quantities
when are formulations useful
pharmaceutical industries have to... make sure it delivers drug to correct part of the body right concentration consumable long shelf life
cleaning products fuels cosmetics fertilisers metal alloys even food and drink
what is chromatography
an analytical method used to separate the substances in a mixture
what is the mobile phase
where the molecules can move (liquid or a gas)
what is the stationary phase
where the molecules can’t move (solid or a really thick liquid)
explain what is meant by equilibrium in chromatography
the substances in the sample are constantly moving between both phases
how does the mobile phase move
it moves quickly through the stationary phase, and anything else dissolved in the mobile phase moves with it.
what does the speed of a chemical depend on in chromatography
how it is distributed between the two phrases- whether it spends more time in the mobile phase or the stationary phase
what will a pure substance look like on a chromatogram
it will only ever form one spot in any solvent as there is only one substance in the sample
what is used as the the stationary phase
chromatography paper
what is used as the mobile phase
the solvent (eg. ethanol or water)
what does the amount of time spent in each phase depend on
how soluble they are in the solvent
how attracted they are to the paper
what will happen when a molecule with a high solubility in the solvent is used in chromatography
will spend more time in the mobile phase, and they’ll be carried further up the paper
what’s the name of the result of the chromatography?
chromatogram
what’s the rf value equation
distance traveled by substance divided by distance traveled by solvent
Different compounds have different what
rf values in different solvents
what can the different rf values be useful for?
can be used to help identify the compounds
what happens to the spots in a mixture
The compounds
in a mixture may separate into different spots depending on the
solvent
what happens in the hydrogen test
The test for hydrogen uses a burning splint held at the open end of a
test tube of the gas. Hydrogen burns rapidly with a pop sound.
what happens in the oxygen test
The test for oxygen uses a glowing splint inserted into a test tube of
the gas. The splint relights in oxygen.
what happens in the CO2 test
The test for carbon dioxide uses an aqueous solution of calcium
hydroxide (lime water). When carbon dioxide is shaken with or
bubbled through limewater the limewater turns milky (cloudy).
