235 234
2) Uranium is used in nuclear reactors and is a rare element on earth. Uranium has three common
isotopes. If the abundance of U is 0.01%, the abundance of U is 0.71%, and the abundance of
U is 99.28%, what is the average atomic mass of uranium?
238

Average atomic mass of uranium = 237.97 amu

Explanation:

Given data:

Abundance of U-234 = 0.01%

Abundance of U-235 = 0.71%

Abundance of U-238 = 99.28%

Average atomic mass of uranium = ?

Solution:

Average atomic mass  = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass) + (abundance of 3rd isotope × its atomic mass)  / 100

Average atomic mass  = (234×0.01)+(235×0.71)+(238+99.28) /100

Average atomic mass =  2.34 + 166.85+23628.64 / 100

Average atomic mass = 23797.83 / 100

Average atomic mass = 237.97 amu.