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

by Rival
Tags: elements
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Rival
#1
Jan20-04, 10:38 PM
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
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himanshu121
#2
Jan20-04, 10:42 PM
himanshu121's Avatar
P: 658
Can u find the no. of moles
Rival
#3
Jan20-04, 10:44 PM
P: 14
how?

himanshu121
#4
Jan20-04, 10:49 PM
himanshu121's Avatar
P: 658
What is this element, carbon, hydrogen, oxyden or aluminum?

1 mole contains 6.02 * 1023 entities here atom
Rival
#5
Jan20-04, 10:54 PM
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?
himanshu121
#6
Jan20-04, 10:56 PM
himanshu121's Avatar
P: 658
yup, N is given to u 30.1 1023
Rival
#7
Jan20-04, 11:00 PM
P: 14
ok so we have 5 moles but now what? how do we figure out what element it is?
himanshu121
#8
Jan20-04, 11:02 PM
himanshu121's Avatar
P: 658
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
himanshu121
#9
Jan20-04, 11:09 PM
himanshu121's Avatar
P: 658
so i feel u got M0=135/5=27

Which belongs to ????(WHAT)
Rival
#10
Jan20-04, 11:13 PM
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...
Rival
#11
Jan20-04, 11:23 PM
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.
himanshu121
#12
Jan21-04, 12:07 AM
himanshu121's Avatar
P: 658
U checked in for Atomic Number Rather than atomic wt

Atomic wt for Al is 27 (Aluminum)

Co is Cobalt
Rival
#13
Jan21-04, 12:19 AM
P: 14
hehe, that could help if i looked for the right thing. Thanks alot, i really appreciate your help.

Kevin
HallsofIvy
#14
Jan21-04, 07:04 AM
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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