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Math Help - Halogen question

  1. #1
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    Halogen question

    Hello
    This question really confused me.... here it is

    The equation shows the reaction between a halogen and the aqueous ions of another halogen.


    X2 + 2Y^- = 2X^- + Y2

    What could X2 be? and that could the colour of Y^- be?


    A) chlorine / brown
    B) chlorine / colourless
    C) iodine / brown
    D) iodine / colourless



    the answer should be B, but how, I reckon if X displaced Y (it did right?), then it must be more reactive, hence it has a lighter colour (as we go down group 7 elements, they get darker in colour) that made me choose A as an answer, which is incorrect :-(

    Any explanation would be very much appreciated
    Thanks
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  2. #2
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    e^(i*pi)'s Avatar
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    Quote Originally Posted by igcsestudent View Post
    Hello
    This question really confused me.... here it is

    The equation shows the reaction between a halogen and the aqueous ions of another halogen.

    X2 + 2Y^- = 2X^- + Y2

    A) chlorine / brown
    B) chlorine / colourless
    C) iodine / brown
    D) iodine / colourless
    the answer should be B, but how, I reckon if X displaced Y (it did right?), then it must be more reactive, hence it has a lighter colour (as we go down group 7 elements, they get darker in colour) that made me choose A as an answer, which is incorrect :-(
    Yes, X displaced Y. It means that X is a stronger oxidising agent (X has gained an electron so it has been reduced) than Y. The oxidising power of the halogens decreases as we go down group 7 (your colour analogy is correct although it's better to talk about oxidation and reduction).


    The question is very badly written because since Cl can displace both Br and I then A and B could apply. Is there another part to the question that would help here?
    Last edited by e^(i*pi); June 5th 2011 at 03:33 PM. Reason: fixing broken quote
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  3. #3
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    thanks :-)
    Last edited by igcsestudent; June 6th 2011 at 01:30 AM.
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