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another chem question

Discussion in 'DAT Discussions' started by arpitpatel86, May 29, 2008.

  1. arpitpatel86

    2+ Year Member

    Joined:
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    8. Iron reacts with element X to form the compounds FeX
    and Fe​
    3X2. When copper reacts with element X, the
    expected compound(s) should be
    A. CuX and Cu
    3X2.
    B. Cu
    2X and Cu6X.
    C. Cu
    3X only.
    D. CuX
    2 only.

    E. Cu
    3X and Cu3X2.

    ANSWRE IS E
    Iron forms the +3 or the +2 ion: Fe​
    3+ (ferric) and Fe2+ (ferrous). The fact that it reacts with X to form FeX and Fe3X2

    suggests that X forms an anion with a –3 charge. X​
    reacts with the ferric ion to form FeX, since both have a –3 charge,
    but reacts with the ferrous ion to form Fe
    3X2 to balance the charge. Copper usually forms either the +1 or the +2 ion.
    When the former reacts with X, then, there must be three Cu
    + ions to balance the charge, resulting in Cu3X. When the

    latter reacts with X, it does so in the same way that the ferrous ion does, forming Cu
    3X2.

    makes sense but i still dont know how to calculate the charges for transition metals...how are we supp to know that copper has a plus 1 and plus 2 charge.....how do we not know if it only has one of those or multiple charges?
     
  2. dentalplan

    2+ Year Member

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    i see what you're saying...r u sure they didn't give the oxidation states to use for iron and copper? If they didn't, i think u were just supposed to assume the most popular oxidation states.

    iron actually can be +1, +2, +3, +4, +5, and +6! copper i think can be +1, +2, +3, and +4. However, the most popular states are +2 and +3 for iron and +1 and +2 for copper. I agree this is a hard question cuz u have to know a little bit about oxidation state physical chemistry.

     

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