Chemistry Problem: Solving with Molar Mass & Isotope Abundance

[cpatel23]

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?

 

[Simon Bridge]

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.

 

[HallsofIvy]

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.