elements?!?!


by Rival
Tags: elements
Rival
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#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
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#2
Jan20-04, 10:42 PM
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P: 661
Can u find the no. of moles
Rival
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#3
Jan20-04, 10:44 PM
P: 14
how?

himanshu121
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#4
Jan20-04, 10:49 PM
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P: 661

elements?!?!


1 mole contains 6.02 * 1023 entities here atom
Rival
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#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
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#6
Jan20-04, 10:56 PM
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P: 661
yup, N is given to u 30.1 1023
Rival
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#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
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#8
Jan20-04, 11:02 PM
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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
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#9
Jan20-04, 11:09 PM
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P: 661
so i feel u got M0=135/5=27

Which belongs to ????(WHAT)
Rival
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#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
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#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
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#12
Jan21-04, 12:07 AM
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P: 661
U checked in for Atomic Number Rather than atomic wt

Atomic wt for Al is 27 (Aluminum)

Co is Cobalt
Rival
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#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
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#14
Jan21-04, 07:04 AM
Math
Emeritus
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Thanks
PF Gold
P: 38,900
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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