# So easy but yet I can't solve it

by cpatel23
Tags: solve
 P: 16 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?
 Homework Sci Advisor HW Helper Thanks PF Gold P: 10,236 While the molar masses do not change, the relative abundances can and do. An element has isotopes X and Y which have molar masses mx and my with percentage abundances px and py ... rearrange those variables to give an equation for the average molar mass for the element.
 Math Emeritus Sci Advisor Thanks PF Gold P: 38,706 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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