Question

Lithium has two naturally occurring isotopes, 6Li and 7Li . The atomic weight of lithium is 6.941. Which of the following statements concerning the relative abundance of each isotope is correct? A) The abundance of 7Li is greater than 6Li. B) The abundance of 7Li is less than 6Li. C) The abundance of 6Li is equal to the abundance of 7Li. D) Not enough data is provided to determine the correct answer. E) Based on the atomic mass, only 7Li occurs naturally.

Answer 1

Answer: The abundance of Li-7 isotope is higher as compared to Li-6.

Explanation:

Average atomic mass is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

$\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i$

We are given:

Two isotopes of lithium :

Li-6 and Li-7

Average atomic mass of lithium= 6.941

As, the average atomic mass of lithium is closer to the mass of isotope Li-7. This means that the relative abundance of Li-7 is higher as compared to Li-6.

Percentage abundance of Li-7> Percentage abundance of Li-6 isotope