QA (qualitative analysis) - cations Flashcards
How are cations distinguished?
Based on their reactions with aqueous sodium hydroxide (NaOH) and aqueous ammonia (NH4)
Added both ______ (observe colour of precipitate formed) then in _____ (solubility) to observe the cation present in the solution
Added both dropwise (observe colour of precipitate formed) then in excess (solubility) to observe the cation present in the solution
Adding NaOH to salt solutions containing transition metal ions (Cu2+, Fe2+, Fe3+) usually form _____ precipitates while adding it to salt solutions containing other metal ions (e.g. Zn2+, Al3+, Pb2+, Ca2+) (except group I + ammonium) form _____ precipitates
Adding NaOH to salt solutions containing transition metal ions (Cu2+, Fe2+, Fe3+) usually form coloured precipitates while adding it to salt solutions containing other metal ions (e.g. Zn2+, Al3+, Pb2+, Ca2+) (EXCEPT group I + ammonium) form white precipitates
Metal hydroxides such as Al(OH)3, Zn(OH)3, Pb(OH)3 are ______ (ie they can react with ____________). In this case, they react with excess sodium hydroxide to form complex salts that are soluble to give a ______ solution.
Metal hydroxides such as Al(OH)3, Zn(OH)3, Pb(OH)3 are amphoteric (ie they can react with both acids and bases). In this case, they react with excess sodium hydroxide to form complex salts that are soluble to give a colourless solution.
Aqueous ammonia is a ____ alkali, hence it dissociates _____ in water.
Aqueous ammonia is a weak alkali, hence it dissociates partially in water.
Zn2+ and a few drops of NaOH: what do you observe?
White precipitate (Zn(OH)2) is formed
Zn2+ and NaOH in excess: what do you observe?
White precipitate soluble in excess NaOH (aq) to form a colourless solution.
Al3+ and a few drops of NaOH: what do you observe?
White precipitate (Al(OH)3) is formed
Al3+ and NaOH in excess: what do you observe?
White precipitate soluble in excess NaOH (aq) to form a colourless solution.
Pb2+ and a few drops of NaOH: what do you observe?
White precipitate (Pb(OH)2) formed
Pb2+ and NaOH in excess: what do you observe?
White precipitate soluble in excess NaOH (aq) to form a colourless solution.
Ca2+ and a few drops of NaOH: what do you observe?
White precipitate (Ca(OH)2) is formed
Ca2+ and NaOH in excess: what do you observe?
White precipitate is insoluble in excess NaOH (aq).
Cu2+ and a few drops of NaOH: what do you observe?
Light blue precipitate (Cu(OH)2) formed
Cu2+ and NaOH in excess: what do you observe?
Light blue precipitate is insoluble in excess NaOH (aq).