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Homework Help: Ion concentration

  1. Nov 5, 2007 #1
    [SOLVED] Ion concentration

    1. The problem statement, all variables and given/known data
    http://img225.imageshack.us/img225/9918/chemch0.jpg [Broken]​

    2. Relevant equations
    C = n/v

    3. The attempt at a solution
    My work is shown up above. Sorry if my work looks a little messy. My answer is 27.6 grams.
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Nov 5, 2007 #2
    I just want someone to tell me if I'am right, and correct me if I'am not.
  4. Nov 5, 2007 #3
    good effort

    your error is in your dissociation equation

    MgBr2 --> Mg+2(aq) + 2Br-(aq)

    the bromide ion is twice the concentration of the MgBr2 so the moles of MgBr2 is half what you calculated (.15/2).

    your mass of MgBr2 is half of your answer
  5. Nov 6, 2007 #4
    But isn't Br supposed to have a subscript of 2?
  6. Nov 6, 2007 #5
    MgBr2 is a compound that dissociates into its ions in water.

    the Br- ions don't stay together in water so you get 2 Br- ions

    Br2 by itself is only written when you are referring to bromine as an diatomic element, not as ions in solution
  7. Nov 6, 2007 #6
    Thanks a lot for the help. :approve:
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