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?

    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...

  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.

  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.
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook