What is this element, carbon, hydrogen, oxyden or aluminum?

  1. 8. [CJ6 14.P.001.] A mass of 135 g of an element is known to contain 30.1 1023 atoms. What is the element?
    carbon
    hydrogen
    oxyden
    aluminum

    This is the question on my Physics practice test for my exam tomorrow. i don't know where to even begin with this one. we haven't really gone over anything like this in class...

    Kevin
     
  2. jcsd
  3. Can u find the no. of moles
     
  4. how?
     
  5. 1 mole contains 6.02 * 1023 entities here atom
     
  6. ok so i am guessing that the equation that i need to use is n=N/NA

    but how do we figure out N?
     
  7. yup, N is given to u 30.1 1023
     
  8. ok so we have 5 moles but now what? how do we figure out what element it is?
     
  9. Do u now approx mol wt of above given elements

    Find the Mol wt with the help of Mole equation

    [tex]n=\frac{g}{M_0}[/tex] where M0 is Mol wt and g is the given wt
     
  10. so i feel u got M0=135/5=27

    Which belongs to ????(WHAT)
     
  11. so using the equation you gave me, i have n = 5 and g = 135, so i find Mo, which came out to be 27, and in the periodic table 27 is Co. what element is Co? but i think its wrong...
     
  12. now that i know the mol wt, i matched it with the periodic table and it comes out to Co, but which one of the choices are Co.
     
  13. U checked in for Atomic Number Rather than atomic wt

    Atomic wt for Al is 27 (Aluminum)

    Co is Cobalt
     
  14. hehe, that could help if i looked for the right thing. Thanks alot, i really appreciate your help.

    Kevin:smile:
     
  15. HallsofIvy

    HallsofIvy 40,229
    Staff Emeritus
    Science Advisor

    The whole point of a "mole" of an element is that it's weight in grams is equal to the weight of an individual atom in "atomic units". Once you know that you can identify the element.
     
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