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Homework Help: Number of Carbon Atoms

  1. Jan 18, 2010 #1
    1. The problem statement, all variables and given/known data

    If you were to count the number of carbon atoms at the rate of four each second, how long would it take you to count 6.0 grams of Carbon atoms?


    2. Relevant equations

    ----

    3. The attempt at a solution

    6.0 g Carbon x [1 mole carbon atom / (6.02 x 10^23 grams )] = 9.97x10^-24 moles carbon atoms

    then my friend told me....

    per one second, three moles.

    therefore, 9.97x10^-24 moles carbon x 4 seconds x 1 / 3 moles carbon
    = 1.33 x 10^-23 s

    I'm having an exam tomorrow and I have a GUT feeling that this'll be asked -__- can someone please help?
     
  2. jcsd
  3. Jan 18, 2010 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    A couple of problems.

    Firstly you need to have the units right.
    Since you wan't an answer in seconds but you are given a speed (ie atoms/second) then you need ot be dividing by 4 somewhere.

    And with these sort of big numbers type questions you need to have some idea of the answer you are looking for.
    You know that atoms are very small, so there must be a lot of them in 6g of carbon, so counting at only 4/s it's going to take for ever - you are looking for an answer that is a very long time.

    the answer (althoug that isn't as important as the points above) is:
    6.0g of C is 0.5 moles (molar mass of carbon is 12)
    So there are 0.5 * 6 E23 atoms in 6g of carbon
    So at 4/s it would take 0.5 * 6 E23 /4 seconds = 7E22 seconds
     
  4. Feb 13, 2010 #3
    Thank you for the guidance! I've looked at the solution you gave to me carefully and studied it ! you made it look so simple :) thank you very much!
     
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