chemical analysis Flashcards
define pure substance
single element / compound not mixed with any other substance
how to check if a substance is pure or a mixture(impure)
heat substance
measure heating point
measure boiling point
if its fixed, the substance is pure
Pure ……… and ……. melt and boil at ……. temperatures. Melting point and boiling point …. can be used to
distinguish ….. substances from mixtures.
Pure elements and compounds melt and boil at specific
temperatures. Melting point and boiling point data can be used to
distinguish pure substances from mixtures.
how can you tell if a substance is a mixture
if the substance melts / boils over a range of temperatures
what is a pure substance in everyday language
a substance that has nothing else added to it
example of a pure substance in everyday life
pure milk
what is a formulation
complex mixture , designed to be a useful product
formulations are made by mixing
carefully measured components so the product has the properties we need
5 examples of formulations
fuels,
cleaning agents,
paints,
medicines,
alloys,
fertilisers
foods.
all separation techniques are …..
physical processes
what does it mean if something is a physical process
doesn’t involve physical reactions
no new substances are made
what does paper chromatography do
separate substances based in different solubilities
how to carry out chromatography
pencil line along bottom of chromatography paper
dot of #1 colour on line
#2 dot next to it
bottom of paper in solvent
what happens in chromatography
solvent makes way up paper and
dissolves ink in 2 coloured dots
what phase is the paper, why
paper- stationary phase, doesn’t move
what phase is the solvent, why
solvent- mobile phase, it moves
why does paper chromatography work
each chemical in mixture is attracted to paper to a different extent
what will happen to chemicals that are strongly attracted to stationary phase (paper)
they wont move very far
what will happen to chemicals that are weakly attracted to stationary phase (paper)
move further up the paper
a pure chemical will produce…..
a single spot in all solvents
the chemicals in a mixture may
separate into different spots depending on solvent
why do we draw starting line in pencil
pen ink would move up paper with solvent
why do we draw starting line in pencil
pen ink would move up paper with solvent
why do we draw starting line in pencil
pen ink would move up paper with solvent
RP- paper chromatography
describe in depth
6 key points
4 add on points
**use ruler- draw horizontal pencil line 2 cm from edge of paper
-X no. of pencil spots, equal intervals, minimum 1 cm away from sides of paper
**glass capillary tube- put small spot of colouring on each pencil spot.
-small spots- stop colours running into eachother
-label spots in pencil
**pour 1cm squared water in beaker
**tape paper to glass rod so bottom of paper dips into water
**remove paper when water is around 3/4 up it
-use pencil, mark point where water reached
**hang paper to dry
***calculate RF value
how do you calculate rf value
distance moved by chemical/ distance moved by solvent
how do you measure distance of chemical
pencil line to centre of dot
what is the solvent front
distance moved by solvent
how would you find out identity of the chemical
look up rf value in database
you want to identify chemical but several other chemicals have same rf value. what do u do
repeat using different solvent to narrow down
what is another solvent u can use in chromatography
ethanol
safety precaution
don’t put chemical in eye- irritation
3 important points to remember in required practical for chromotography
pencil line with ink above water
paper x touch side of beaker
use lid
why is pencil line with ink spots drawn above the water
otherwise water will wash off ink
why is paper not allowed to touch walls of beaker
this will interfere with how water moves
why do we use a lid
to prevent evaporation
what happens once practical is set up
water moves up beaker and carries up colours
when do we remove paper
when water is 3/4 up
2 things we do after we remove the paper
draw line where water reached
hang up to dry
how do you know if chemical hasn’t been analysed before
x rf value on data base
what would you do if chemical hasn’t been analysed before
carry out further analysis to identify it
how to test for hydrogen
hold burning splint at end of open test tube of gas
positive test for hydrogen
hydrogen burns rapidlt with squeaky pop sound
The test for …… uses a burning ….. held at the open end of
a test tube of the gas. Hydrogen burns ….. with … sound.
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.
how to test for oxygen
glowing splint inserted into test tube of gas
positive test for oxygen
splint bursts into flames (relights)
how to test for co2
gas shaken with / bubbled through limewater
what is limewater
aqueous solution of calcium hydroxide
(calcium hydroxide dissolved in water)
positive test for co2
repeat bubbling/ shaking gas with limewater and turn s cloudy
how to test for chlorine
insert damp litmus paper into test tube of gas
positive test for chlorine
chlorine bleaches litmus paper. turns it white
what are flame tests used for
identifying an unknown compound
which contain a metal ion
how to carry out flame test
2 steps
small amount of chemical onto wire on a handle.
put end in blue bunsen burner flame
what is the colour of the flame used for
to identify the metal ion present
what colour flame produced by lithium
crimson
what colour flame produced by sodium
yellow
what colour flame produced by potassium
lilac
what colour produced by calcium
orange red flame
what colour flame produced by copper
green
problem with using flame test to identify metal ion
colour hard to distinguish
especially if low concentration of metal ion
some samples contain mixture of metal ions, masking colour of flame
what can be used instead of flame tests
flame emission spectroscopy
what happens in flame emission spectroscopy
3 points
. sample of metal ion put into a flame
. light given out passed into spectroscope
. spectroscope converts light into line spectrum
what is flame emmision spectroscopy used for.
analysing metal ions in a solution
the line spectrum can be
analysed to….
identify the metal ions in the solution
+
measure concentration of metal ions
what is important to know about the positions of the lines in the spectrum
the position of the lines are specific for a given metal ion
what does more intense lines mean in flame emission spectroscopy
higher concentration
hat does instrumental method mean
carried out by a machine
3 advantages of instrumental methods
rapid
sensitive
accurate
