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Verify that the number of atoms Avagadro's constant

  1. Dec 9, 2009 #1
    "verify that the number of atoms..." Avagadro's constant

    1. The problem statement, all variables and given/known data

    One mole of a substance is defined as an amount, in grams, numerically equal to its molecular mass expressed in amu. (when we refer to a chemical element and not a compound, we use the atomic mass.) Verify that the number of molecules (or atoms) in one mole of any substance is the same, and is equal to 6.0225 x 10^23. This number, called Avogadro's constant, is a very important physical constant.

    I've just started trying to learn physics, and this problem appeared in one of the questions that are at the end of each chapter.
    The book is "Alonso-Finn Fundamental University Physics. Book 1: Mechanics"
    The question is question number 2.8
    I am taking a physics course next year and would like to learn as much as I can before I go into the class.
    2. Relevant equations
    Avogadro's Constant: 6.0225x10^23

    Not sure what else is needed.

    3. The attempt at a solution

    I've attempted a couple times but, I am not sure how to set up an equation properly as to get a result. The problem states that it will work with any substance, although i've been told that it only works for carbon-12? [6.0225x10^23 = 1 gram so 1 gram X 12amu = 12grams]

    Any and all help to point me in the right direction is appreciated!

    Thanks, John.
  2. jcsd
  3. Dec 9, 2009 #2


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    Science Advisor
    Homework Helper

    Re: "verify that the number of atoms..." Avagadro's constant

    Hi, welcome to PF.
    Sounds like a bit of a circular argument.
    1 mole is defined as 6.02E23 of anything, and an AMU is defined so that 6.02e23 of them is a gram.

    The carbon bit is mostly for convenience. Atoms come in different isotopes with different nuber of nuetrons and so different AMU masses. Carbon is handy because its mostly C12 and its (farily) easy to separate out other isotopes
  4. Dec 10, 2009 #3


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    Staff: Mentor

    Re: "verify that the number of atoms..." Avagadro's constant

    Not exactly - mole is so far defined as

    (see http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf)

  5. Dec 10, 2009 #4
    Re: "verify that the number of atoms..." Avagadro's constant

    I've figured it out! Quite simple once I was pushed in the right direction.

    Molar mass constant/ avogadro's constant or M(subscript)u/N(subscript)a
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