How to calculate molar mass of a natural sample of lithium, referring to textbook Fundamental E11

[Christian_Lee_2K]

The nuclear power industry extracts but not from natural samples of lithium. As a result, the molar mass of commercial samples of lithium is increasing. The current abundances of the two isotopes are 7.42% and 92.58%, respectively, and the masses of their atoms are 9.988*10^-24 and 1.165*10^-23 respectively. (A) what is the current molar mass of a natural sample of lithium?

Why we would add and . I thought we would only use because it is asking for the natural sample and only is pulled from a natural sample.

[Lily Jiang 3K]

I think you have misunderstood the question. The problem only mentions the extraction of Li-6 to explain the increasing molar mass of commercial Li. To solve for the molar mass, you still need to use the given abundances for Li-6 and Li-7, not just Li-6.

Molar Mass = (abundance of Li-6 * molar mass of Li-6) + (abundance of Li-7 * molar mass of Li-7)