Gcse: Tests for Anions and Cations Flashcards
Flame tests - lithium
Gives a red flame
Li+ ions
Flame tests sodium
Gives a yellow flame
Na+ ions
Flame tests potassium
Gives a lilac flame
K+ ions
Flame tests calcium
Gives an orange red flame
Ca2+ ions
Flame tests copper
Gives a blue green flame
Cu2+
Flame tests method
Clean a nichrome wire loop by dipping it in hydrochloric acid and then rinsing it in distilled water
Dip the wire loop into a sample of the metal compound and put in the clear blue part of the Bunsen flame
Precipitate test aluminium
Turn right at first but then re-dissolves in excess sodium hydroxide to form colourless solution
Al3+(aq) + 3OH-(aq) —-> Al(OH)3(s)
Then:
Al(OH)3(s) + OH- (aq) —-> Al(OH)4-(aq)
Precipitate test calcium
Turns white
Ca2+(aq) + 2OH-(aq) —-> Ca(OH)2(s)
Precipitate test copper
Turns blue
Cu2+(aq) + 2OH-(aq) —-> Cu(OH)2(s)
Precipitate test iron II
Turns green
Fe2+(aq) + 2OH-(aq) —-> Fe(OH)2(s)
Precipitate test iron III
Turns brown
Fe3+(aq) + 3OH-(aq) —-> Fe(OH)3(s)
Test for ammonium ions
NH4+
Add sodium hydroxide to your solution of your substance and heat it,
test for ammonia gas by holding damp red litmus paper over it,
if the gas is ammonia the litmus paper will turn blue
Halide test method
To test for halide ions and dilute nitric acid followed by a few drops of silver nitrate solution
Halide test chloride ions
Forms white precipitate of silver chloride
Ag+(aq) + Cl-(aq) —-> AgCl(s)
Halide test bromide ions
Forms cream precipitate of silver bromide
Ag+(aq) + Br-(aq) —-> AgBr(s)
Halide test iodide ions
Forms yellow precipitate of silver iodide
Ag+(aq) + I-(aq) —-> AgI(s)
Test for carbonates method
To test for carbonate ions in solution and some dilute acid
if there are carbonate ions present the mixture will fizz
this is because the carbonate will react with the acid to produce carbon dioxide gas
you can check to see if the gas is carbon dioxide by bubbling it through limewater
if it is the limewater turns milky
Test for sulphate ions method
To test for sulphate ions in solution add dilute hydrochloric acid to the test sample (this stops any precipitation reactions not involving sulphate ions from taking place)
then add barium chloride solution
if sulphate ions are present a white precipitate of barium sulphate will form
Flame photometry purpose
Flame photometry is an instrumental method that allows you to identify ions in a dilute solution
each ion produces a unique line spectrum
flame photometry works for mixtures this makes it better than flame tests
