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    i have 3 questions about this lesson
    1-complex ions are formed in solutions only or can a crystal exist with a complex ion(like H2O molecules act as ligands)
    2-how can i know how many H2O molecules are there
    for example
    http://s13.postimg.org/t9emu8scn/screenshot_61.png
    after this question it asks what is the formula of compound A
    the answer is FeSO4.7H2O
    how did I know that it is 7?
    3-I've read in a book that when adding excess NaOH to chromium 3+ solution it dissolves to a green solution forming [Cr(H2O)2(OH)4]- but it then written in the exam that it forms [Cr(OH)6]3-
    which one is right or both of them?
    thanks in advance
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    (Original post by bubakazouba)
    i have 2 questions about this lesson
    1-complex ions are formed in solutions only or can a crystal exist with a complex ion(like H2O molecules act as ligands)
    2-how can i know how many H2O molecules are there
    for example
    http://s13.postimg.org/t9emu8scn/screenshot_61.png
    after this question it asks what is the formula of compound A
    the answer is FeSO4.7H2O
    how did I know that it is 7?
    thanks in advance
    1. No, not in solution only. Yes, also in crystalline solids, eg hydrated copper)II) sulphate.

    2. There are a huge number of possible hydrated salts. You can't know which one is being asked in advance. That is why you have the analysis information to work with.
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    (Original post by charco)
    1. No, not in solution only. Yes, also in crystalline solids, eg hydrated copper)II) sulphate.

    2. There are a huge number of possible hydrated salts. You can't know which one is being asked in advance. That is why you have the analysis information to work with.
    1-i thought the ones in CuSO4 are water of cyrstallisation not acting as ligands

    2-yeah thats why I've put the whole question with the analysis information in the image
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    (Original post by bubakazouba)
    1-i thought the ones in CuSO4 are water of cyrstallisation not acting as ligands

    2-yeah thats why I've put the whole question with the analysis information in the image
    Ligand just means 'linked to'.

    In hydrated salts, the water molecules surround the metal ions in the same way as in complex ions. There may be some adjustment to incorporate the anions into the structure, but the fundamental structure is still there.

    This can be shown by the colour of the crystals when hydrated and dehydrated.

    The very fact that copper(II) sulphate crystals are the same colour as the solution demonstrates that the ions are surrounded by the water ligands and the 'd' orbitals are split by the same amount.
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    (Original post by charco)
    Ligand just means 'linked to'.

    In hydrated salts, the water molecules surround the metal ions in the same way as in complex ions. There may be some adjustment to incorporate the anions into the structure, but the fundamental structure is still there.

    This can be shown by the colour of the crystals when hydrated and dehydrated.

    The very fact that copper(II) sulphate crystals are the same colour as the solution demonstrates that the ions are surrounded by the water ligands and the 'd' orbitals are split by the same amount.
    hmm ok I think I understood this, may you answer 2 and 3 please
 
 
 
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