Testing for cations

Question 1

Cu^2+ (aq) (Copper ion)

Answer 1

Add sodium hydroxide solution, observe the colour of the precipitate
Cu^2+ (aq) + 2OH^- (aq) -> Cu(OH)2 (s)
Blue ppt (precipitate)

Question 2

Fe^2+ (aq) (Iron (II) ion)

Answer 2

Add sodium hydroxide solution, observe the colour of the precipitate
Fe^2+ (aq) + 2OH^- (aq) -> Fe(OH)2 (s)
Green ppt (precipitate)

Question 3

Fe^3+ (aq) (Iron (III) ion)

Answer 3

Add sodium hydroxide solution, observe the colour of the precipitate
Cu^3+ (aq) + 3OH^- (aq) -> Fe(OH)3 (s)
Brown ppt (precipitate)

Question 4

NH4^+ (ammonium ion)

Answer 4

Add sodium hydroxide solution, (this time it will not form a precipitate) collect the gas given off, place damp (needs to be damp because it reacts with the water) red litmus paper into it, if it turns blue then ammonium ions are present. (The gas should be amonnia gas)
NH4^+ (aq) + OH^- (aq) -> NH3(g) + H2O(l)