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Question regarding empirical formula and molecular formula(finding 2 variables)A Lvel

  1. Mar 5, 2012 #1
    1. The problem statement, all variables and given/known data

    http://www.xtremepapers.com/CIE/International A And AS Level/9701 - Chemistry/9701_s11_qp_12.pdf

    question 10




    2. Relevant equations




    3. The attempt at a solution
    The way I am doing it, is to get two equations in terms of x and y and then equate them. For the first equation I used the fact that all of the element's individual atomic masses will add up to 571.5. So i got 27x + 28.1y = 172
    My problem now is how to get the second equation? I think it has something to do with the empirical formula, but I can't figure it out. Help!
     
  2. jcsd
  3. Mar 6, 2012 #2
    Re: question regarding empirical formula and molecular formula(finding 2 variables)A

    If you remove the Al and Si from the formula, what is the charge on the resulting ion?
     
  4. Mar 6, 2012 #3

    Borek

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    Staff: Mentor

    Re: question regarding empirical formula and molecular formula(finding 2 variables)A

    What is 14.04% of 571.5?
     
  5. Mar 6, 2012 #4
    Re: question regarding empirical formula and molecular formula(finding 2 variables)A

    I think I got it, thanks to you. So for x we find 14.17% of 571.5. That answer we divide by 27, (because we know that the mole of aluminium is 1), and the x i got is 2.999(pretty close to one of the options). Same for y. Thanks!
     
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