Testing for ions Flashcards
why do we use the flame test
to identify a positive metal ion in an unknown compound
what colour flame does: Lithium? Sodium? Potassium? calcium? barium?
produce
Lithium- crimson Sodium- yellow Potassium- lilac calcium- red barium- green
other than the flame test, what can we use to identify positive ions?
reactions with sodium hydroxide
which 3 ions form a white precipitate when mixed with sodium hydroxide
calcium ions
aluminium ions
magnesium ions
what happens if you add an excess amount of sodium hydroxide to aluminium ions?
it redissolves
what colour precipitate is formed when you add sodium hydroxide to copper (II) ions
blue
what colour precipitate is formed when you add sodium hydroxide to iron (II) ions
green
what colour precipitate is formed when you add sodium hydroxide to iron (III) ions
brown
how do we test for carbonate ions (negative ions)
add dilute acid to sample
bubble gas produced into limewater
if it turns milky that means carbon dioxide is present proving there’s carbonate ions
how do we test for halide ions (negative ions)
add nitric acid to sample
then add silver nitrate
if a precipitate is formed, halide ions are present
why do we add nitric acid to test halide ions?
to dissolve the compound and remove any carbonate ions because they form a precipitate with silver ions, interfering with the experiment
which ions are present if a
white precipitate is formed
cream precipitate is formed
yellow precipitate is formed
chlorine ions
bromine ions
iodine ions
how do we test for sulphate ions (negative ions)
add hydrochloric acid to sample
add barium chloride solution
if sulphate ions are present a white precipitate will form
