chemical analysis Flashcards
what is chemical analysis
the instruments and methods used to
seperate
identify
quantify
different substances
what are examples of chemical analysis
chromotography
crystallisation
distillation
filtration
define a pure substance
something that contains only 1 types of compound or element
what are 2 examples of pure substances
distilled water
sodium chloride
why is it important to know purity of substances
only pure subtances melt and boil at specific temps
mp of nacl
801 degrees
example of how can we use a physical test to identify substances
boil unknown liquid
it boils at 100 degrees
we can be quite sure it is water
what is a chemical test
reacting a substance with another chemical to determine what it is is chemical
what is a physical test
testing physical properties(eg mp or bp) and looking them up in big data book to find match
state the mp and bp patterns for impure substances
they melt and boil over large range of temps
what does having impurities in a sample generally do
lower mp
increase bp
what is the mp/bp for salt water
mp=-2 degrees
bp=100.5 degrees
what are formulations
mixtures prepared using specific formula
How and why are formulations made
-so they have precise amounts of different components
-have a particular function
what are 7 examples of formulations
fuels
cleaning agents
paint
medicines
alloys
fertilisers
food and drink
describe the idea of formulations to a recipe and meal
a recipe that makes a mixture for a specific purpose
what is the rule with formulations
the different components(that give diff properties) are in carefully measured quantities
what is are the components needed in the formulation of green paint
green colour
stick to the wall
many others
what is paper chromotography used for
to seperate different dyes in an ink
which are
mixtures of soluble substances in liquids
what is the 1st step of paper chromotography
draw line near bottom of sheet of a4 filter paper called baseline using pencil.
what is the 2nd step of paper chromatography
add sample of ink(that you think has many dyes) in centre of baseline
what is the 3rd step of paper chromotography
put a shallow amount of solvent like ethanol or water into beaker
what is the 4th step of paper chromotography
put filter paper into solvent but dont submerge the baseline
what is the 5th step of paper chromotography
place lid so solvent does not evaporate
results after step 5 of paper chromatography
solvent seeps up paper different dyes that make up ink dissolve in solvent and move up with it
how does paper chromatograpy seperate different substances
each dye travels at different rates an d seperate out
why may stay some chemicals stay on the baseline
as they arent soluble in solvent so they cant dissolve and move up paper
what is the 6th step of paper chromotography
take filter paper out and leave it to dry when solvent has almost reached top of paper
what is a chromatogram
the pattern of spots we have left on our filter paper
what is the mobile phase
substance that molecules can move in
typically liquid or gas
what is the mobile phase in chromatography
solvent used
what is the stationary phase
substance that molecules cant move in
typically solid or very thick liquid
what is the stationary phase in paper chromatography
paper
what happens to the chemicals in the ink sample in terms of phases in paper chromatography
they constantly change between the mobile and stationary phases
what is an example of changes in phases in paper chromatography
dissolving in solvent
moving slightly
binding to paper
repeat
what determines how fast chemicals in paper chromatography move up paper
how long they spend in each phase
what is the relation between solubility and speed in paper chromatography
more soluble in spends more time in mobile phase so goes faster and travels further up paper
less soluble spend more time in stationary phase so are slower and wont travel far up paper
what makes less soluble chemicals slower
as they are more attracted to the paper
how can we identify chemicals in paper chromatography
measure how far substance move and compare it to a data book
what 2 factors affect how far chemicals move up paper
properties of substance
how long we leave experiment
what is the rf value
a ratio
what is the equation for the rf value
distance travelled by substance/
distance travelled by solvent
what happens to a pure substance in paper chromatography
doesnt seperate out at all
-appears as a dot on the chromatogram
what may change the rf value you get for a pure substance
using different solvent
diff type of paper
Why should we use pencil for the baseline rather than pen?
Pen ink would dissolve in the solvent and move up the paper tampering with experiment
what is the rf value of a substance specific to
stationary phase(paper)
solvent(mobile phase)
1st step in chlorine test
get test tube full of sample gas(which u think may be chlorine)
2nd step in chlorine test
dampen blue litmus paper
3rd step in chlorine test
put litmus paper into test tube
what happens if chlorine is present in step 3 of cl test
litmus paper goes blue—–>white
why may chlorine briefly go red before turning white in cl test
it dissolves in water forming hcl which is acidic and turns blue litmus red
why does litmus go back to white after turning red
it gets bleached by the chlorine
what /why precautions are taken in cl test
cl is poisonous so wear mask or perform it in a fume cupboard
what is needed in o2 test
a glowing splint
sample of gas
explain steps of o2 test
place splint into tube and if it relights its oxygen
why does the splint relight in o2 test
burning requires o2
equipment needed for h2 test
burning splint
test tube sample
what happens if h2 is present in h2 test
squeaky pop heard as splint is brought near
why is squeaky pop heard in h2 test
heat energy from flame causes hydrogen to burn with o2 in air to form water
what is equipment for co2 test
test tube of gas sample
test tube of colourless limewater( aq calcium hydroxide)
steps for co2 test
bubble sample gas into limewater test tube
solution goes cloudy if it is co2
why does solution go cloudy in co2 test
co2(g) and ca(oh)2(g) react to form caco3(s) and h20(l)
caco3 is solid and its small solid particles make it appear cloudy
