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    i'm doing edexcel chemistry and i'm confident that i know most of the complex ion colours but there are several i'm unsure about due to disagreeing sources in books/websites, so if anyone could tell me, for sure, what happens in the following scenarios (whether ppt dissolves & if so, what colour the solution is), i'd be grateful:

    1) Cr3+ in excess NaOH
    2) Cr3+ in excess NH3
    3) Co2+ in excess NaOH
    4) Co2+ in excess NH3
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    Cr3+ in excess NaOH, the green ppt will redissolve to form a dark green solution
    Cr3+ in excess NH3, no change beyond deprotination (ppt will remain)

    Co2+ in excess NaOH should have no change
    Co2+ in excess NH3, will form a blue solution.

    Ive done tis from memory so not garunteed to be correct but I'm pretty sure that's what it says in my textbook.
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    right, thanks for clearing that up
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    dont forget that the Co2+ ppt formed with NaOH will turn grey on standing as cobalt II gets oxidised by the oxygen in the air to cobalt III - this effect is seen almost immediately near the surface and soon spreads through the whole ppt.
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    [CuCl4]- is yellow
    my alevels are over.. so good luck!
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    (Original post by mik1w)
    Co2+ in excess NH3, will form a blue solution.
    Is not right...

    If you add NH3 dropwise you will first form a blue precipitate of cobalt (II) hydroxide.

    This in excess NH3 will form a pale yellow solution of [Co(NH3)6]2+

    [Co(NH3)6]2+ is oxidised in air to from a brown solution of [Co(NH3)6]3+

    I'll let you off cuz i know how hard they are to remember!
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    you switched from cobalt to copper halfway through so I dont understant but...

    I am checking my textbook for edexcel chemistry unit 5 and it says the ammonia will perform ligand exchange with the hydroxide ions to form a blue solution of [Co(NH3)6]2+

    plus he asked for the colours of Co2+ in excess, not what you would see if you added it dropwise
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    Soz, i corrected it now...

    Besides, it would be [Cu(NH3)4(H20)2]2+ (deep blue) anyway if it was copper

    Well, my book says [Co(NH3)6]2+ is pale yellow
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    ive got a textbook that says [Co(NH3)6]2+ is pale straw.. which i guess is yellow but when my class did a practical in which we added excess NH3 to Co2+ we got blue solutions, so i think i'm gona go with mik1w's answer
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    Go with what your textbook says.
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    hmm.. well the guy whose website this is was chief examiner for edexcel chemistry until last year:
    http://www.rod.beavon.clara.net/prelim.htm
    but he reckons Ni2+ gives pink solution with excess NH3 which disagrees with both my textbooks (that both say blue)
    i'll just have to wait til wednesday to find out from my teacher :confused:
 
 
 
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Updated: June 13, 2005
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