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Calculating Empirical Formulae

  1. Feb 24, 2007 #1
    Hi. Im having problems with finding the empirical formulae

    What is the emprical formula of magnesium nitride if 0.72g of magnesium combines with 0.28g nitrogen?

    So what would my first step be? Find magesuim... which would be 0.44g?
    Can you take me through the steps?

  2. jcsd
  3. Feb 25, 2007 #2


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    I would start by converting your Mg and N into moles. The basic idea is to look at the ratios of one substance to another to find the emiprical formula.

    I don't know why you subtracted up there. Mass must be conserved, so if you start out with 0.72g and 0.28g, how much must you have after the reaction?
  4. Oct 1, 2010 #3
    First calculate the number of moles of both of them by dividing each by their atomic weights.
    Moles are obtained

    Now divide each mole by the smallest mole obtained i.e. 0.02 mole of nitrogen, ratio obtained will be 1.5 of magnesium and 1 of nitrogen

    as 1.5 is not a whole number multiply it by 2 to get a whole number and you will get as 3 and 2 respectivley. thus from this you can get that 3 moles of magnesium reacts with 2 moles of nitrogen to give magnesium nitride.

    I hope this will help you out.
  5. Oct 1, 2010 #4
    Hahaha thanks :D But a little late, I did my GCSE chemistry over 3 years ago and got my A - never said thank you hage567. Infact, I'm starting university tomorrow!

    Thomas :)
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