Question

what is the percentage abundance of each isotope if Lithium has 2 isotopes with a mass number 6 and 7 respectively. If the relative atomic mass of lithium is 6.94?

Answer 1

Answer:

The atomic mass of lithium is 6.94, the naturally occurring isotopes are 6Li = 6.015121 amu, and 7Li = 7.016003 amu. Determine the percent abundance of each isotope.

Answer 2

Answer:

The percentage abundance of the isotope of mass 6 u is 6% and of the isotope of mass 7 u is 94%.

Explanation:

Let the fractional abundance of the lighter isotope be $x$.

Then the fractional abundance of the heavier isotope is $1-x$.

We know,

Average atomic mass = ∑(Atomic mass of an isotope)×(Fractional abundance)

or, 6.94 = $6x - 7(1-x)$

or, $6.94 = 6x +7-7x$

or, $6.94 = 7-x$

or, $x = 7-6.94$

or, $x = 0.06$

Here the fractional abundance of both the isotopes are 0.06 and 0.94.

Hence the percentage abundance of the isotope of mass 6 u is 6% and of the isotope of mass 7 u is 94%.