Chapter 2, Problem 24E

Variations in average atomic mass may be observed for elements obtained from different sources. Lithium provides an example of this. The isotopic composition of lithium from naturally occurring minerals is 7.5% ${}^6\text{Li}$ and 92.5% ${}^7\text{Li}$, which have masses of 6.01512 amu and 7.01600 amu, respectively. A commercial source of lithium, recycled from a military source, was 3.75% ${}^6\text{Li}$ (and the rest ${}^7\text{Li}$). Calculate the average atomic mass values for each of these two sources.