Question

Boron has two isotopes, one with a mass of 10 and the other with a mass of 11. Given that boron has an atomic mass of 10.8, what is the fractional abundance of 10B?

Answer 1

Hi,
This is an easy one

The given value for Boron (10.8) is an average valu calculate using the mass of 11B and 10B according to their abundance

10.8 =( percentage of abundance of 10B * 10) +( percentage of abundance of 11B *11)

if 10B's abundance is x % , the abundance of 11B is (100 - x) %

using that theorem

10.8 = [(x/100) * 10 ]+[ (100-x)/100 * 11]
1080 = 10x + 1100 - 11x
x = 20

that's it !!!
10B is abundance is 20% which is 1/5

Hope this will help u out