Question

the atomic weight of boron is 10.811. the natural abundance of 10B is 19.91%. Determine the atomic weight of the only other natural isotope of boron

Answer 1

Another natural boron isotope is ^xB. ^xB and ¹⁰B form the average atomic weight of boron:

$10 * 0.1991 + X * (1-0.1991) = 10.811$, where X -- the atomic mass of another boron isotope;

$1.991 + 0.8009*X = 10.811$

$0.8009*X = 8.82$

$X = 11$

The atomic weight of the only other natural isotope of boron is 11.