CHEMICAL ANALYSIS Flashcards
a pure substance is
how does boiling point/melting point tell you about purity of a substance
how can you test the purity of a sample
single element or compound not mixed w/ any other substance
pure element/compound will melt+boil a specific temperatures
measure melting/ boiling point + compare w/ melting/boiling point of pure substance from data
what does pure substance mean in everyday language
how will impurities in a sample alter melting point.
how will impurities in a sample alter boiling point
a substance that has nothing added , unadulterated, in its natural state.
Lower melting point AND increase melting range of substance
increase boiling point + result in sample boiling over range of temps
what is a formulation
how are formulations made
a complex mixture designed as a useful product where each chemical has a particular purpose
-mixing components in carefully measured quantities to ensure the product has the required properties.
examples of formulations x7
f
f
f
c
p
m
a
fuels
fertiliser
foods
cleaning agent
paints
medicines
alloys
why are formulations important in pharmecuticals industry
make a pill have long shelf life
make a pill consumable
make sure drug in pill delivered to right part of body at right concentration
POSITIVE TESTS FOR :
chlorine
oxygen
carbon dioxide
hydrogen
–chlorine - bleaches damp litmus paper white . (blue paper may turn red momentarily bcse chlorine solution is acidic)
–oxygen-glowing splint inserted into test tube of gas. splint relights in oxygen
–carbon dioxide- bubble carbon dioxide through/shake with an aqueous solution of calcium hydroxide (limewater). limewater turns milky(cloudy)
–hydrogen-burning splint held at open end of test tube of gas. Hydrogen burns rapidly w/ ‘‘squeaky pop’’ sound
how would you fill a test tube w/ hydrogen
and how w/ chlorine
why do it differently
hold tube upside down, gas will rise to fill it.
hold test tube right way up and gas will sink to bottom
depends on whether gas is heavier/ lighter than air
Chromatography used to separate….
-process - 6 steps
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.why do you see different spots
separate substances based on different solubilities
-draw pencil line on chromatography paper - near bottom
-put dot of first colour on pencil line and dot of second next
-place bottom of paper in solvent- make sure solvent doesn’t touch ink
-put lid on to stop solvent evaporating
-solvent makes its way up paper dissolves ink in coloured dots
-ink is carried up paper as well
-when solvent front is at almost at top of paper, remove paper+ let dry
-each dye in ink will move at different rate- dyes will separate out- each dye will form spot in 1 place
why do we draw starting line in pencil
-why should ink spot not touch solvent
pencil marks are insoluble- won’t dissolve in solvent
-don’t want spot to dissolve into solvent
what solvents can be used
Rf value =
depends on what’s being tested- some compounds dissolve well in water-
other solvents- eg ethanol - may be needed
-distance moved by substance / distance moved by solvent
no unit…
what is the solvent front
-how do you measure distance moved by chemical
point the solvent has reached up the paper
-from pencil line to centre of spot
what is the stationary phase
what is mobile phase
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how to tell if a colour is pure
how to tell if a colour is a mixture
the paper, it does not move
solvent is the mobile phase as it moves
- (a pure compound) will produce a single spot in all solvents
-compounds in a mixture may separate into different spots depending on the solvent used
why does paper chromatography work
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how to identify an unknown substance
different substances have different solubilities . A more soluble substance travels further up the paper than a substance that is less soluble. That way we can seperate substances based on solubility
-workout Rf value and compare to datatbase
if 1+ substances have this Rf value than compare it in other solvents
(if substance never analysed bfor, rf value x be on database)
if any dyes in the ink are insoluble in the solvent they will….
-what would happen if you used pen to draw starting line
they’ll stay on the baseline
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-components in ink will separate out along with substance your analysing
RP- chromatography
-sample of unknown colouring and known colorings
-draw pencil line and 5 pencil spots- equal intervals
-capillary tube used to put all colorings on pencil spots
-put water in 1 cm deep
-attach paper to glass rod with tape-lower into water- should dip into water
-put lid on to prevent evaporation of solvent
-remove paper when water travelled 3/4 up
-use pencil-mark point where paper reached and hang to dry
things to remember x5
-keep dots small-stop colors spreading into eachother
-sides of paper must not touch walls of beaker- will interfere with water movement
-don’t move beaker
-pencil line with ink should be above surface of water- or ink will be washed off the line
FLAME TEST COLOURS
Lithium = crimson
(a CRIMSON LIpstick
Sodium = yellow
(SO DAMN LOUD –> yellow is a loud colour)
Potassium = lilac
(LILAC flowers in flower POTs)
Calcium = orange-red
(CALum Scott is hot )
copper = green
(COPs are good guys- good things are green)
-flame tests used to identify……
-the ……. of these metals produce distinctive colours in flame tests
-where do we put the chemical to be tested
metal ions- cations
the compounds of the metals
-small amount on wire with a handle and place into blue flame
problems w/ flame tests x2
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-alternative to flame tests-
-what type of method is this
-colour can be hard to distinguish esp. if low conc. of metal compound
-some samples have a mixture of metal ions- masks colours of flame
-flame emission spectroscopy
-instrumental method
how does flame spectroscopy work
-sample of metal ion in solution put into flame and light given out passed through spectroscope
-spectroscope converts light into line spectrum
-analyse line spectrum to identify metal ions in solution and concentration
-how do we know what metal ion and the concentration present
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-what does instrumental method mean-
-position of lines specific for each metal ion
-lines become more intense w/ higher concentration
-carried out by machine
3 advantages of instrumental method -flame emission spectroscopy
-accurate- more likely to correctly identify the metal ion
-sensitive-works on tiny sample of compound
-rapid- can use it to identify metal ions more rapidly than flame tests
what can sodium hydroxide solution be used for-
WHEN ADDED TO THESE IONS WHITE PRECPITATE formed-
-which ions
-how would you easily identify 1 metal ion from this
-how would you work out other 2
-to identify SOME metal ions- cations
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-added to solutions of AL, Mg, Ca,- white precipitates formed
-when u add excess sodium hydroxide, the Al hydroxide precipitate dissolves
-flame test
the hydroxide test for cations (metals)
what colour precipitate is made
copper(II) – Cu²⁺ Blue precipitate remains
Iron(II) – Fe²⁺ Green precipitate remains
Iron(III) – Fe³ Red-brown precipitate remains
Magnesium – Mg² White precipitate remains
Aluminium – Al³⁺ White precipitate dissolves to form a colourless solution
Calcium – Ca² White precipitate remains
formula for aluminium, calcium, magnesium nitrate-
Are the the metal solution you add sodium hydroxide to- aq, s, l
-sodium hydroxide formula
-is the sodium hydroxide solution aq, s, l
Ca(NO₃)₂
Mg(NO₃)₂
Al(NO₃)₂
aq
-NaOH
-aq
calcium nitrate + sodium hydroxide=
metal nitrate(aq) + sodium hydroxide(aq)=
sodium nitrate + calcium hydroxide
metal hydroxide(s) + sodium nitrate (aq)
formula for sodium nitrate
2NaNO₃
SODIUM HYDROXIDE SOLUTION (aq)+ METAL ION SOLUTIONS (aq)= METAL HYDROXIDE(s) + SODIUM NITRATE
-AL, Mg, Ca form white precipitate(Al one dissolves w/ excess sodium hydroxide= colourless solution)
-what are the other three metal ions we can test for
-what coloured precipitates do they form
copper ll-blue
iron ll-green
iron lll-brown
formula for- and charge
nitrate
hydroxide
-NO₃…..-1
-OH ……-
identifying non metal ions- anions
-what are the three types of non metal ions to test for-
carbonate ions
halide ions
sulfate ions
how do you test for carbonate ions
-add dilute acid to sample
-ACID should react w/ CARBONATE to make CO2
-see effervescence
TEST TO MAKE SURE IT’s CO2
-bubble gas through lime water
-if lime water goes cloudy- we have CO2 therefore we had a carbonate ion in beginning
how to test for halide ions
- add dilute nitric acid to sample
-add dilute silver nitrate solution
-halide ions produce precipitate of the silver halide- each halide forms diff. colour precipitate
What colour are the precipitates of….
-Chloride ion + silver nitrate solution
-bromide ion + silver nitrate solution
-iodide ion + silver nitrate solution
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-white precipitate- silver chloride
-cream precipitate- silver bromide
-yellow precipitate- silver iodide
how to test for sulfate ion
-add dilute hydrochloric acid to sample
add barium chloride solution
-if sulfate ions present, see white precipitate
