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Quick question on moles

  1. Jul 7, 2009 #1
    Trying to get my head around moles and molarity. I ran into this problem.

    How many moles of O are in 4.5 moles of P2O5? Having trouble figuring it out, can anyone help?
  2. jcsd
  3. Jul 7, 2009 #2
    I think I have figured it out...

    22.5 moles?
  4. Jul 7, 2009 #3
    New problem I am having difficulty with...

    How many moles of C is needed to react with 5.0 moles of H to form C3H8?

    Gonna need help with this one!
  5. Jul 7, 2009 #4
    Try using ratios of the elements.
  6. Jul 7, 2009 #5
    Thanks. I got 1.875. pretty easy. Just a bit tricky for a beginner.
  7. Jul 7, 2009 #6
    It's ok. The only reason why it's easy for experts (I'm not necessarily one) is because they struggled with these problems until they picked it up.
  8. Jul 7, 2009 #7
    You already know how to work with moles. Don't think of it as some abstract concept, but rather think of it in terms of something you can relate to. Just think of moles as something like a dozen. How many potatoes, eggs, or ears of corn are in a dozen? You know the answer to this. How many atoms of carbon, hydrogen, platinum are in a mole? It's all the same. If a recipe calls for 6 eggs for every 3 cups of flour, how many dozen eggs would you need for 9 cups of flour? It's the same idea with moles.
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