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So easy but yet I can't solve itby cpatel23
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#1
Jan2714, 09:19 PM

P: 17

Hello.
I am doing a chemistry problem but it is mainly mathematics Here it is. A little info that is useful to this problem. Molar mass is always an average, given by Molar Mass = (mass of isotope1 * abundance of isotope 1) + (mass of isotope2 + abundance of isotope 2) Masses of isotopes are always constant, they do not vary from place to place. So how do I solve this? 


#2
Jan2714, 09:59 PM

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P: 12,791

While the molar masses do not change, the relative abundances can and do.
An element has isotopes X and Y which have molar masses m_{x} and m_{y} with percentage abundances p_{x} and p_{y} ... rearrange those variables to give an equation for the average molar mass for the element. 


#3
Jan3014, 05:11 PM

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PF Gold
P: 39,510

If we are to assume that the two isotopes given here are the only ones we need consider, then let "x" be the relative abundance of the first (U235) and then the relative abundance of the other (U238) is 1 x.
So we must have x(235.043924)+ (1 x)(238.050784)= 238.0375. Solve that equation for x. 


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