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    I'm reacted hexaaqua copper/nickel/zinc (2+ all) with OH- and excess NH3

    My book gives the following reactions:
    Nickel:
    (Ni(H20)6)2+ + 2OH- ==> Ni(H20)4(OH)2 + 2H20
    (Ni(H20)6)2+ + 6NH3 ==> (Ni(NH3)6)2+ + 6H20

    Copper:
    (Cu(H20)6)2+ + 2OH- ==> Cu(H20)4(OH)2 + 2H20
    (Cu(H20)6)2+ + 4NH3 ==> (Cu(NH3)4(H20)2)2+ + 4H20

    Zinc:
    (Zn(H20)6)2+ + 2OH- ==> (Zn(H20)3(OH)3) + 2H20
    (Zn(H20)6)2+ + 6NH3 ==> (Zn(NH3)6)2+ + 6H20

    Questions...
    1) The second copper reaction looks wrong. Why does it say only 4 out of 6 water molecules get replaced with ammonia? My CGP book could be wrong...
    2)For zinc, the first reaction looks odd. Wouldn't it have 2 OHs to make the compound neutral? Is my book wrong again?

    I've looked at another book (George facer) but it doesn't give specific reactions I think for all the metals I need

    Thanks
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    (Original post by Phalange)
    I'm reacted hexaaqua copper/nickel/zinc (2+ all) with OH- and excess NH3

    My book gives the following reactions:
    Nickel:
    (Ni(H20)6)2+ + 2OH- ==> Ni(H20)4(OH)2 + 2H20
    (Ni(H20)6)2+ + 6NH3 ==> (Ni(NH3)6)2+ + 6H20

    Copper:
    (Cu(H20)6)2+ + 2OH- ==> Cu(H20)4(OH)2 + 2H20
    (Cu(H20)6)2+ + 4NH3 ==> (Cu(NH3)4(H20)2)2+ + 4H20

    Zinc:
    (Zn(H20)6)2+ + 2OH- ==> (Zn(H20)3(OH)3) + 2H20
    (Zn(H20)6)2+ + 6NH3 ==> (Zn(NH3)6)2+ + 6H20

    Questions...
    1) The second copper reaction looks wrong. Why does it say only 4 out of 6 water molecules get replaced with ammonia? My CGP book could be wrong...
    2)For zinc, the first reaction looks odd. Wouldn't it have 2 OHs to make the compound neutral? Is my book wrong again?

    I've looked at another book (George facer) but it doesn't give specific reactions I think for all the metals I need

    Thanks
    Your first question is actually quite complicated to answer as it involves something called the Jahn Teller effect which makes the axial sites in the copper(II) complex longer then the equatorial and leaves them more labile. This means that there is rapid exchange beween species at this position.

    Your second question about the zinc equation. You are correct, the equation is wrong. They seem to have got confused between the simple sodium hydroxide addition giving the zinc hydroxide and the excess addition creating the soluble zincate ion.

    Addition of NaOH to zinc ions first makes a precipitate which redissolves on addition of excess NaOH

    [Zn(H2O)6]2+ + 2OH- --> [Zn(H2O)4(OH)2](s) + 2H2O

    and

    [Zn(H2O)6]2+ + 4OH- --> [Zn(H2O)2(OH)4]2-(aq) + 4H2O
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    (Original post by charco)
    Your first question is actually quite complicated to answer as it involves something called the Jahn Teller effect which makes the axial sites in the copper(II) complex longer then the equatorial and leaves them more labile. This means that there is rapid exchange beween species at this position.

    Your second question about the zinc equation. You are correct, the equation is wrong. They seem to have got confused between the simple sodium hydroxide addition giving the zinc hydroxide and the excess addition creating the soluble zincate ion.

    Addition of NaOH to zinc ions first makes a precipitate which redissolves on addition of excess NaOH

    [Zn(H2O)6]2+ + 2OH- --> [Zn(H2O)4(OH)2](s) + 2H2O

    and

    [Zn(H2O)6]2+ + 4OH- --> [Zn(H2O)2(OH)4]2-(aq) + 4H2O
    Thank you so much That cleared it all up
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    Isn't the second equation of the hexaaqua zinc(II) complex (ligand exchange reaction with excess NH3) also incorrect? I believe it should be:
    [Zn(H2O)6]2+ + 4NH3 ? [Zn(H2O)2(NH3)4]2+ + 4H2O,
    or are both generally accepted?
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    Zinc is unusual. Most hexaaqua ions with +2 charge rarely react with OH- beyond the precipitate.

    When zinc reacts with excess OH- it forms the tetrahedral structure [Zn(OH)4]2- where the ion has lost the two remaining water ligands.

    Therefore from the precipitate, the reaction is:

    [Zn(H2O)4(OH)2](s) + 2OH-(aq) ==> [Zn(OH)4]2-(aq) + 2OH-(aq) + 2H2O(l)
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    Writing the equation from the original from the original hexaaqua ions is also perfectly acceptable.
 
 
 
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