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Homework Help: Calculating Moles of O Atoms?

  1. Sep 16, 2007 #1
    Calculate the number of moles of O atoms in 13.27 g Mn(NO3)2.

    Hi I did this question and it seemed pretty easy but there is this online assignment im doing it for and it says im not getting the right answer.

    Please can someone try it and see if they get what i do, or tell me what im doing wrong

    My Solution:

    mass (13.27g) x

    1 mole
    ------------------------------- x
    MM of Mn(NO3)2 (178.96g/mol)

    6 atoms of O
    ----------------- = .4449 mol
    1 mole

    When i submit my answer it says Incorrect!!!!!

    I dont understand whats wrong with that
  2. jcsd
  3. Sep 17, 2007 #2


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    Science Advisor
    Homework Helper

    You need the molar mass of the whole compound ie Mn + 2N + 6O = x
    Then calculate how many moles of this is in 13.27g
    Finally you have 2 moles of oxygen for each mole of the compound.
  4. Sep 17, 2007 #3

    2 moles of oxygen in each compound>?

    ther are 6 moles of oxygen not 2

    and the molar mass is wrong that i said up ther?
  5. Sep 17, 2007 #4


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    Homework Helper

    Sorry typo - meant to say 6. I couldn't follow your equations so I was trying to describe how to do it in simple terms.

    I get the same answer, you might want to try 0.445 mol if the question site is dumb and is just using whole number masses.
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