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pure substance
a substance only containing one element or compound
how can you test for the purity of a substance?
boiling and melting point and comparison to a data book
will impurities lower or raise the melting point of a substance?
lower
will impurities lower or raise the boiling point of your sample?
raise
formulations
mixtures with a precise purpose
chromatography is a ...... method
analytical
why do we do paper chromatography?
separate the substances in a mixture / is it pure?
mobile phase in chromatography
water (always a liquid or gas) - molecules can move
stationary phase in chromatography
paper (solid) - molecules can't move
Rf value calculation
distance travelled by substance / distance travelled by solute
why would an Rf value change?
different temperatures or different solvent
test for chlorine
Bleaches damp litmus paper
test for oxygen
Relights a glowing splint
Test for carbon dioxide
Turns limewater cloudy
test for hydrogen
Lighted splint gives a squeaky pop
what is an anion
A negatively charged ion
examples of anions
carbonates (CO3 2-) , Sulphates (SO4 2-) , Halides (Cl- , Br- , I-)
Test for carbonates
First add dilute acid (hydrochloric acid)
If carbonate ions (CO3 2-) are present carbon dioxide will be released and will turn limewater cloudy
test for sulphates
add drops of dilute hydrochloric acid and drops of barium chloride, if white precipitate if present
test for halides
Add dilute nitric acid and then silver nitrate solution, coloured precipitates form
why can't you use hydrochloric acid in test for halides
contains chloride ions - would give a false positive
chloride precipitate
White precipitate of silver chloride
bromide precipitate
cream precipitate of silver bromide
iodide pecipitate
yellow precipitate or silver iodide
What is the first step of the flame test method?
Dip nichrome/platinum wire into dilute HCl to sterilize it and burn it in a blue flame in a Bunsen burner until it burns without any color.
What is the second step of the flame test method?
dip loop in the sample and record the colour of the flame produced when the sample is burned.
disadvantages of flame test
only works for samples containing a single metal ion, if a mixture then some colours could be hidden by others
Lithium ions flame test
crimson flame
Sodium ions flame test
yellow flame
Potassium ions flame test
Lilac flame
Calcium ions flame test
Orange-red flame
Copper ions flame test
Green flame
what do you add in a metal precipitate test (cations)
sodium hydroxide
calcium precipitate
white
Copper precipitate
blue
Iron (II) precipitate
green
Iron (III) precipitate
brown
Aluminium precipitate
white - redissolves in excess NaOH
Magnesium precipitate
white
Note 
Flashcard (43)