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Why does 1 mole of NaCl contain 1 mole each of Na and Cl?

  1. Jul 16, 2012 #1
    "A mole of sodium chloride is 58.443 g. It will contain 6.022 x 1023 chloride ions and 6.022 x 1023 sodium ions"

    Why does one mole of sodium chloride contain both a mole of chloride AND a mole of sodium? Why not half a mole of each?:confused:
  2. jcsd
  3. Jul 16, 2012 #2
    Every NaCl molecules has a Na and a Cl atom. So, if you have 6.022x10^23 molecules, you will have that same number of Na atoms and Cl atoms, and by definition, 1 mole is 6.022x10^23 atoms
  4. Jul 16, 2012 #3


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    Science Advisor

    A mole is a number - like a dozen. It's like asking, "Why does a dozen cats contain a dozen heads and a dozen tails, and not half a dozen of each?"
  5. Jul 16, 2012 #4
    I know what a mole is. But, why does it have to be a mole of each instead of another (equal) number?

    Could I have a mole of NaCl with Na and Cl consisting of 1 atom each (for a total of two atoms in the NaCl)? If I have 6.022 x 10^23 of the NaCl (with two atoms total rather than a mole each) would it still be 1 mole of NaCl? or is there some reason I need to have 1 mole of each atom?
  6. Jul 16, 2012 #5


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    Staff: Mentor

    As phyzguy wrote - if you have dozen cats, they have a dozen heads and dozen tails. If you have a dozen of NaCl molecules, they have a dozen Na and a dozen Cl atoms. If you have a mole of NaCl, it has a mole of Na and a mole of Cl. It can't be any other number, just like dozen cats can't have ten heads, as two of the cats would be not a cats, but decapitated cats.
  7. Jul 18, 2012 #6
    In NaCl, the ratio of Na to Cl to NaCl is 1:1:1.
    If you don't believe me look at the equation Na + Cl -> NaCl and look at the coefficients.
    A mole is 6.023*10^23. Therefore, if you have a mole of NaCl, multiplying the ratio by the number will give you

    6.023*10^23 Na : 6.023*10^23 of Cl : 6.023*10^23 NaCl.

    6.023*10^23 atoms of Na = 1 mol of Na.
    6.023*10^23 atoms of Cl = 1 mol of Cl.
    6.023*10^23 molecules of NaCl = 1 mol of NaCl.

    Isn't avagadros number fun! Now you can do some weight percentage problems like: if you had 20g of NaCl, what percent of the weight is due to the presence of sodium.
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