Chemical Analysis Flashcards
what is a pure substance?
a single element or compound, not mixed with any other substance
how can we find out if a substance is pure using its mp/bp?
Pure substances melt and boil at a specific temp
what is a formulation?
a mixture that has been designed as a useful product eg. paint, fuel, medicine, alloys, fertilisers
how are formulations made?
mixing the components in carefully measured quantities to ensure that the product has the required properties
what phases does chromatography have?
- mobile phase=where molecules can move eg. a liquid or gas
- stationary phase=where molecules can’t move eg. a solid or really thick liquid
what are the phases in paper chromatography?
- stationary phase=chromatography (filter) paper
- mobile phase=solvent eg. water/ethanol
what is the time molecules spend in each phase affected by?
- how soluble they are
- how attracted they are to the paper
- high solubility+less attracted to paper=more time in mobile phase=further up the paper
what is an Rf value?
ratio between distance travelled by solute and distance travelled by solvent
Rf value equation
distance moved by substance/distance moved by solvent
how can we identify pure substances with chromatography?
- pure compounds will produce a single spot in all solvents
what are Rf values dependent on?
solvent
- changing solvent=different Rf values
required practical: chromatography
- like normal chromatography but Rf value calculated
test for hydrogen
squeaky pop test
- burning splint held at the open end of a test tube of the gas
- hydrogen burns rapidly with a pop sound
test for oxygen
- glowing splint inserted into a test tube of the gas
- splint relights in oxygen
test for CO2
- aqueous solution of calcium
hydroxide (lime water) - CO2 is shaken with or
bubbled through limewater the limewater turns milky/cloudy
test for chlorine
- damp litmus paper is
put into chlorine gas - litmus paper is bleached and turns white (may turn red first because chlorine solution=acidic)
flame tests
- lithium=crimson flame
- sodium=yellow flame
- potassium=lilac flame
- calcium=orange-red flame
- copper=green flame
- a sample containing a mixture of ions is used some flame colours can be masked
metal hydroxide tests
- calcium - white precipitate
- magnesium - white
- aluminium - white+dissolves in excess sodium hydroxide solution=colourless
- iron (II) - green
- iron (III) - brown
- copper - blue
equations for metal hydroxides
- calcium
Ca+2 + 2OH- –> Ca(OH)2 (s) - magnesium
Mg+2 + 2OH- –> Mg(OH)2 - aluminium
Al+3 + 3OH- –> Al(OH)3 - iron (II)
Fe+2 + 2OH- –> Fe(OH)2 - iron (III)
Fe+3 + 3OH- –> Fe(OH)3 - copper
Cu+2 + 2OH- –>Cu(OH)2
carbonates test
- add a couple drops of dilute acid eg. HCl to your solution in a test tube
- using a bung, connect test tube with solution with a test tube with limewater
- if CO2 released, limewater=milky/cloudy
halides test
- add a couple drops of dilute nitric acid (HNO3)
- add a couple drops of silver nitrate (AgNO3)
- chlorine - white
- bromine - cream
- iodine - yellow
sulfates test
- use a dropping pipette, add a couple drops of dilute HCl+barium chloride (BaCl2) to a test tube with the solution you’re testing
- barium sulfate will form if barium is present
- Ba+2 + SO4 -2 –> BaSO4
what are instrumental methods?
- a way of detecting+identifying elements/compounds
pros of instrumental methods
- very sensitive - detect tiny amounts
- very fast - can be automated
- vary accurate
flame emission spectroscopy
- an instrumental
method used to analyse metal ions in solutions - sample is put into a flame=electrons become excited
- electrons drop back to original energy level=transfer energy as light
- light given out is passed
through a spectroscope=detects different wavelengths=produces line spectrum - combination of wavelengths emitted by ion depend on its charge+electron arrangement
- different ions=different wavelengths=different line spectrum
- intensity of spectrum=concentration
