PAPER 2 REQUIRED PRACTICALS Flashcards
rate of reaction
use a measuring cylinder to put 10cm3 of sodium thiosulfate solution into a conical flask
place conical flask onto printed black cross
add 10cm3 of HCL into conical flask
swirl solution and start stopwatch
look down into flask after a certain time the solution will turn cloudy, stop the stopwatch when you can no longer see the cross
repeat experiment again using lower concentrations of sodium thiosulphate solution
repeat whole experiment and calculate mean values for each concentration of the sodium thiosulphate solution
what shouldn’t you do when working out the mean values
use anomalies
problems with the rate of reaction
people have different eyesight that means that some people can see the cross for longer than others
however all the students use the same size cross
volume of a gas from reaction
use measuring cylinder to place 50cm
attach conical flask to a bong and delivery tube
place an upturned measuring cylinder filled with water over the delivery tube
add 3cm strip of magnesium to the hcl and start stopwatch
the reaction produces hydrogen gas which is trapped in the measuring cylinder
every 10 seconds measure volume of hyderogen gas in measuring cylinder until no hydrogen is given off
repeat experiment using different concentrations of HCL
what do both rate of reaction experiemts show
the greater the concentration of a chemical in a reaction the faster it takes place
paper chromatography
use a ruler to draw horizontal line on paper it should be 2cm from the bottom of the paper
mark pencil spots at equal spaces across the line
put the spots on the line using a capillary tube
pour water in beaker- attack paper to glass rod with selotape and dip the paer into water
make sure that the line is above the surface of the water so that the ink doesn’t wash off
use a pencil line to mark where water reached
compare the different colourings with the unkniwn colour
things to watch when doing paper chromatography
pencil line above surface of water
sides of the paper shouldn’t touch the sides of the beaker if this happens it will interfere with the way the water moves
lid to reduce the evaporation of the solvent
how do you work out rf value
distance moved by solvent
what does rf value tell you
the identity of the chemical
flame tests
lithium-crimson sodium- yellow potassium- lilac calcium- orange/red copper-green
lithium flame test
crimson
sodium flame test
yellow
potassium flame test
lilac
calcium flame test
orange/red
copper flame test
green
barium flame test
green
problems with the flame test
colour of flame test can be difficult to distinguish
if there is a low concentration of the metal compound
sometimes a sample contains a mixture of metal ions which mask the colour of the flame
copper ii ions reaction with sodium hydroxide
blue precipitate of copper hydroxide
iron ii ions reaction with sodium hydroxide
green precipitate of iron hydroxide
iron iii ions reaction with sodium hydroxide
brown precipitate of iron hydroxide
why are instrumental methods eg spectroscopy better than flame tests
you can analyse samples more rapidly than you could with flame tests
they are more sensitive flame emission spectroscopy will work even on a tiny sample of metal compound
instrumental methods are accurate, flame emission spectroscopy is more likely to identify a metal ion correctly than using a flame test
non metal ions
carbonate
halides
sulfate
test carbonate
add nitric acid to sample
the acid will react with the carbonate to make co2 gas we will see effervescence
bubble the gas through limewater, if the limewater goes cloudy this proves we have carbon dioxide
test for halides
add dilute nitric acid to sample then add dilute silver nitrate solution
halide ions produce a precipitate of silver halide. each halide makes a different coloured precipitate
