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Preparation of Tetraamine copper ii sulfate-1-water??

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    Hello. Any help in explaining would be much appreciated

    In the preparation of tetramine copper (ii) sulfate-1-water crystals, to obtain the crystals of the solution, I added ethanol and cooled the solution.
    Why couldn't we just heat and evaporate, i.e. crystallize like usual? Does something happen to the complex if heated?
    And what about the ethanol and cooling caused the precipitation of the crystals?

    The equation if it helps:
    [Cu(H2O)4 (OH)2] (s) + 4NH3 (aq) = [Cu(NH3)4(H20)2] 2+ (aq) + 2OH- (aq) + 2H2O (l)

    Thanks!
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    You know reaction happens because delta G<0 => delta H is most likely < 0, so heat disfavours exothermic reaction eqm.

    Another way I look at it is that evaporating the water might cause the ligand to fall apart, ie you could get anhydrous copper amine ligands in the end(my speculation).

    And in crystallisation process, as far as i know, you usually heat them up first, ie to concentrate the solution, then you cool them down. Recrystallisation then involves dissolving this cooled crystal with minimum amount of cold ethanol or other appropriate solvent(depends on experiments) and cool them further in ice bath.
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    (Original post by shengoc)
    Another way I look at it is that evaporating the water might cause the ligand to fall apart, ie you could get anhydrous copper amine ligands in the end(my speculation).
    Thats pretty reasonable. Thanks!


    (Original post by shengoc)
    And in crystallisation process, as far as i know, you usually heat them up first, ie to concentrate the solution, then you cool them down. Recrystallisation then involves dissolving this cooled crystal with minimum amount of cold ethanol or other appropriate solvent(depends on experiments) and cool them further in ice bath.
    I did the second part (in bold) only. When I added cold ethanol to the solution and cooled it in an ice bath, the precipitate just simply formed and was filtered for the crystals. And I was wondering what about the cold ethanol caused this?
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    (Original post by mirah12)
    Thats pretty reasonable. Thanks!




    I did the second part (in bold) only. When I added cold ethanol to the solution and cooled it in an ice bath, the precipitate just simply formed and was filtered for the crystals. And I was wondering what about the cold ethanol caused this?
    Tbh, I don't know too, feeling a little bit embarrassed, :woo:
    But it is usually kept to a minimum, and it is also used to wash the remaining crystals formed in the flask(again minimum amount too). But this is a normal procedure for recrystallisation, together with scraping the flask with glass rods, to promote crystal growth
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    (Original post by shengoc)
    Tbh, I don't know too, feeling a little bit embarrassed, :woo:
    But it is usually kept to a minimum, and it is also used to wash the remaining crystals formed in the flask(again minimum amount too). But this is a normal procedure for recrystallisation, together with scraping the flask with glass rods, to promote crystal growth
    Don't worry about it; thanks for the info anyway
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    thats the wrong equation guys, you said: tetramine copper (ii) sulfate-1-water crystals
    and that is [Cu(NH3)4]SO4.H2O..:confused:

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Updated: February 19, 2012
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