Question

Lithium has two isotopes.
Li-6 and Li-7.
Li-6 mass = 6.015121amu
Li-7 mass = 7.016003amu
Lithium Mass = 6.94049amu

What is percent abundance of Li-6?

I know that there is an equation:
6.9409 = (% Abundance Li-6 * Weight of Li-6) + (% Abundance Li-7 * Weight of Li-7)

I don't know how to use it.

Answer 1

you have all 4 pieces, plug them in

Answer 2

Okay. SO 6.9409 = % Li-6 * 6.015121 + % Li-7 * 7.016003
But this gives me two variables...

Answer 3

100% is the sum of the two.
100% = Li 6 + Li 7
Li 6 = 100% Li7

Answer 4

So 6.409 = %Li-6 * 6.015121 + (100% - %Li-6) * 7.016003
Confused...
100% * 7.016003 = 701.6003? That is a big number.

Answer 5

Well ask yourself if this statement makes sense:

The percent abundance of Li-6 is 701.6%.