chemical analysis Flashcards
what does pure mean and how can you test it
not mixed with another substance (one compound or one element)
has specific fixed melting and boiling points, so when heated, temperature will stop rising at specific times to change state. impure will change over a range of
what is a formulation with examples
complex mixture designed for specific purposes. quantities of components carefully measures to get properties for function
paint, medicine
how could you identify an unknown substance
• draw pencil line near bottom of chromatography paper
• add dots of substance on line
• place bottom into solvent
• allow substance and solvent to stop travelling
• measure distance between pencil line and centre of spot
• measure distance between pencil line and solvent
• calculate Rf (substance/solvent)
• look Rf value up in a database to identify
• repeat with other solvents to narrow it down further
how does chromatography work
• there are two phases:
mobile - solvent, molecules move
stationary - paper, doesnt move
• solvent dissolves ink in dots and carries them up paper
• different substances are differently distributed between two phases, depending on solubility
• this means they spend different amounts of time in mobile/stationary
• pure colours have only one substance, so produce single spot in all solvents
• mixtures have different substances with different attractions to phases in different substances, so produce multiple spots
how to test if a gas in a test tube is hydrogen
remove bung and insert burning splint
if present: squeaky pop
reason: hydrogen burns quickly
how to test if a gas in a test tube is oxygen
insert glowing splint
if present: splint will relight
how to test if a gas in a test tube is carbon dioxide
bubble gas through limewater, an aqueous solution of calcium hydroxide, using pipette
if present: limewater turns cloudy
how to test if a gas in a test tube is chlorine
insert damp litmus paper
if present: paper bleaches white
how to identify metal ions in unknown samples
• soak end of splint into sample
• hold over blue bunsen flame
• identify metal from colour of flame
colour of flame for different ions
lithium - crimson
sodium - yellow
potassium - lilac
calcium - orangey red
copper - green
when finding metal ions in unknown samples, what does it mean if the colour of flame is not clear and what can you do identify it
sample had low concentration of metal compound, or it was a mixture
flame emission spectroscopy
what is flame emission spectroscopy
• sample placed in flame
• light given out when energy is released is passed into spectroscope, which converts the light into a light spectrum
• position of lines in spectroscope is specific to a metal ion, as charge and electron arrangements are different in all ions. this means we can identify ion from spectrum
• intensity of the lines show concentration. this means we can calculate the ions concentration
advantages of instrumental analysis methods such as flame emission spectroscopy
very fast - faster than flame test
very sensitive - tiny samples tested
very accurate
how can you use sodium hydroxide solution to identify metal ions in an unknown sample
add NaOH to the separate solutions to produce an insoluble hydroxide.
colour of precipitate will identify
what does it mean if precipitate is white after adding NaOH
it is either calcium, magnesium or aluminium
• add excess NaOH. aluminium precipitate redissolves and goes colourless
what metal ion does each colour identify when NaOH added
calcium - white
magnesium - white
aluminium - white - colourless
copper II - blue
iron II - green
iron III - brown
what does “test for anions” mean and what does “test for cations mean”
anions: test for non-metal ions
cations: test for metal ions
how can you test if a sample contains carbonate
add dilute acid. sample will fizz.
bubble through limewater
present: limewater goes cloudy
what halide ions can be tested for and what colour precipitate do they produce
chloride: white prcpt of silver chloride
brmide: cream prcpt of silver bromide
iodide: yellow prcpt of silver iodide
how can you test if a sample contains halide ions
add dilute nitric acid then silver nitrate solution.
present: coloured precipitate
reason: halide ions produce precipitate of silver halide
how can you test if a sample contains sulfate ions
add dilute hydrochloric acid then barium chloride solution
present: white precipitate (of barium sulfate)
what does it mean when there is a precipitate formed
one of the products of the reaction is a solid
