Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Determining an empirical formula

  1. Aug 3, 2011 #1


    User Avatar

    If I know the percentage by weight of elements in a formula I can calculate the relative ratios of atoms in the formula no problem.

    What I can't figure out is how to turn that ratio into an empirical formula.

    To put it mathematically how do I turn a decimal number into a an approximate fraction of small integers?

    #.## = ?/?

  2. jcsd
  3. Aug 7, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    You should be able to write those decimal numbers as the ratio of small whole numbers.*** For example, 1.25=5/4, 0.67=2/3, etc.

    After you convert all the decimals to small-number ratios, multiply every fraction by a whole number to get whole-number-coefficients.

    *** If you can't get small whole numbers, then something is fishy. Either the molecule is very complex, or there was an error made somewhere. For introductory chemistry problems, it should always work out to small whole numbers.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook