Question

Boron obtained from borax deposits in Death Valley consists of two isotopes. They are boron-10 and boron-11 with atomic masses of 10.013 amu and 11.009 amu, respectively. The atomic mass of boron is 10.81 amu (see periodic table). Which isotope of boron is more abundant, boron-10 or boron-11?

Answer 1

Given:

m1 = 10.013 amu

m2 = 11.009 amu

m = 10.81 amu

use:

atomic mass = sum of (mass of isotope * abundance) / 100

m = (m1*A1 + m2*A2)/100

10.81 = ( 10.013*A1 + 11.009*(100-A1))/100

10.81 = ( 10.013*A1 + 1100.9- 11.009*A1))/100

A1 = 20.0 %

So,

A2 = 100 - A1

= 100 - 20

= 80 %

Clearly 2nd isotope is more abundant

Answer: boron-11