chemical analysis

pure substance

-only pure substances melt and boil at specific temps

diff between physical and chemical test

physical= testing physical propeprties

chemical= reacting with other chemicals

impure substances

melt and boil at diff temps

what are formulations

chromotography

paper chromotography

paper chromotography in 6 steps

1 draw a line with a pencil near the bottom of filter paper- BASELINE

2 add sample of ink to the pencil line

3 fill beaker with shallow amount of solvent (water/ethanol)

4 place filter paper into the solvent

5 wait for solvent to seep up the paper

6 once solvent reaches top take the paper out and leave it to dry (results are called- CHROMOTOGRAPH

what can u do to improve accuracy of paper chromotography

• use pencil instead of ink as ink would dissolve and move up

• make sure pencil line and spot of ink dont submerge (that is the reason why the water in the beaker is shallow)

• place a lid on top of the beaker to stop the solvent from evaporating

analysis of dyes in paper chromotography

if any chemicals arent soluble = stays on baseline

diff dyes will travel at diff rates = seperates= meaning each one is a diff substance

mobile phase

substance molecules can move in (liquid/gas)- in this case solvent in the beaker

stationary phase

materials molecules cant move in (solid/thick liquid)- paper used

how does mobile and stationary phases work during paper chromatography

• diff chemicals will constantly change between mobile and stationary

  dissolves in solvent→ moves a bit → binds to paper → repeat

=how much they spend in each phase determines how fast they move up the paper

more/less soluble ink=

more= longer time in mobile phase =faster

less= longer in stationary= slower

what is Rf and why is it that way

ratio of how far the compound travels

NOT DISTANCE bcs how long the paper has waited in the solvent can also determine the distance

how far each substance travels depends on

its properties

what happens to paper chromotography with a pure substance

wont seperate out and stay as a single spot =has a specific Rf value

HOWEVER id the solvent/ paper type of different the chromatogram will be different= diff Rf vlaue

how to test for chlorine

put a damp litmus paper inside the test tube with gas sample

if present: BLUE→ WHITE

-poisinous: mask or fume cupboard

during test for chlorine why might the litmus paper turn red before bleaching white

bcs chlorine dissolves in water which forms hydrochloric acid.

acidic=red

how to test for oxygen

place glowing splint into the test tube with sample gas

if oxygen is present, it will relight the splint.

this is bcs burning requires oxygen

how to test for hydrogen

put a lit splint inside the test tube with the gas sample.

if present: squeaky pop

bcs heat energy causes hydrogen to burn with oxygen = forms water

how to test for carbon dioxide

bubble gas sample through limewater

if present: limewater will go cloudy

bcs Calcium carbonate formed is a solid= makes it appear cloudy