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Homework Help: Finding the least molar mass of organic compound having molar mass > 100

  1. Jul 26, 2012 #1
    1. The problem statement, all variables and given/known data

    In an organic compound of molar mass > 100 containing only C, H , N, the percentage of C is 6 times the percentage of H while the sum of the percentages of C and H is 1.5 times the percentage of N. What is the least molar mass?

    2. Relevant equations

    C% + N% + H%= 100%
    therefore, 1.5N%+ N%= 100%

    3. The attempt at a solution
    From the above equation that I manage to calculate, N% should be 40%, the next step that I want to take is just not coming exactly to me, though I had a rough idea from the hints given in the question, but finally didn't actually manage to get the exact answer.
  2. jcsd
  3. Jul 27, 2012 #2
    Three unknowns, two equations.

    Which means that you won't be able to solve this exactly. There won't be one unique solution to the percentages of the elements. It can stand for a variety of molecules, each with a different molar mass and HENCE the question asks you to go for the molecule with the least molecular mass.

    1) Solve linear equations as much as you can
    2) When you are done with the solving part, list out ALL possible molecules, you'll find a pattern to them and you'll find that they are many.
    3) But the least one will stand out!
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