Chemistry - Tests for Cations Flashcards
2 different solutions that can be used (to test for cations) ->
Aqueous NaOH and NH3
Dropwise NaOH can result in…
Gas production, white precipitate or coloured precipitate
Dropwise NaOH with NH4+ produces…
Ammonia gas (which can be tested with damp red litmus)
Dropwise NaOH with Al3+ produces…
White precipitate
Dropwise NaOH with Zn2+ produces…
White precipitate
Dropwise NaOH with Ca2+ produces…
White precipitate
Dropwise NaOH with Fe2+ produces…
Green precipitate
Dropwise NaOH with Fe3+ produces…
Red precipitate
Dropwise NaOH with Cr3+ produces
Grey-green precipitate
Dropwise NaOH with Cu2+ produces…
Blue precipitate
Adding excess NaOH has 2 options…
Precipitate may redissolve or it may stay
Adding excess NaOH to Al3+ results in…
Soluble precipitate
Adding excess NaOH to Zn2+ results in…
Soluble precipitate
Adding excess NaOH to Cr3+ results in…
Soluble precipitate
Adding NaOH to everything (apart from Al3+, Zn2+ and Cr3+) results in…
Insoluble precipitate (the precipitate remains)
Dropwise NH3 can result in…
No visible reaction, white precipitate or coloured precipitate
Dropwise NH3 with NH4+ results in…
No reaction
Dropwise NH3 with Ca2+ results in…
No visible reaction
Dropwise NH3 with Al3+ results in…
White precipitate
Dropwise NH3 with Zn2+ results in…
White precipitate
Dropwise NH3 with Fe2+ results in…
Green precipitate
Dropwise NH3 with Fe3+ results in…
Red-brown precipitate
Dropwise NH3 with Cr3+ results in…
Green precipitate
Dropwise NH3 with Cu2+ results in…
Blue precipitate
Adding excess NH3 in Zn2+ results in…
Soluble precipitate (redissolves)
Adding excess NH3 in Cu2+ gives…
Soluble precipitate
(redissolves).
Dark blue solution is produced
Adding excess NH3 in everything (except Zn2+ and Cu2+) gives…
Insoluble precipitate (the precipitate stays)
(TRIVIA): Produces white precipitate when NaOH is added dropwise, but doesn’t react visibly with any NH3
Ca2+
(TRIVIA): With NaOH, these ions will form a white precipitate AND redissolve.
Zn2+ and Al3+
(TRIVIA): With NaOH, this ion forms an insoluble blue precipitate.
Cu2+
(TRIVIA): This ion produces a green precipitate with drops of NaOH but it is dissolved when more is added.
Cr3+
