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

by Rival
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 P: 14 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
 P: 658 Can u find the no. of moles
 P: 14 how?
 P: 658 What is this element, carbon, hydrogen, oxyden or aluminum? 1 mole contains 6.02 * 1023 entities here atom
 P: 14 ok so i am guessing that the equation that i need to use is n=N/NA but how do we figure out N?
 P: 658 yup, N is given to u 30.1 1023
 P: 14 ok so we have 5 moles but now what? how do we figure out what element it is?
 P: 658 Do u now approx mol wt of above given elements Find the Mol wt with the help of Mole equation $$n=\frac{g}{M_0}$$ where M0 is Mol wt and g is the given wt
 P: 658 so i feel u got M0=135/5=27 Which belongs to ????(WHAT)
 P: 14 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...
 P: 14 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.
 P: 658 U checked in for Atomic Number Rather than atomic wt Atomic wt for Al is 27 (Aluminum) Co is Cobalt
 P: 14 hehe, that could help if i looked for the right thing. Thanks alot, i really appreciate your help. Kevin
 Math Emeritus Sci Advisor Thanks PF Gold P: 39,488 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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