Question

What is the average atomic mass of Boron if it exists as 19.90% boron-10 and 80.10% boron-11?

A) 10.81 amu
B) 10.01 amu
C) 11.01 amu
D) 10.45 amu

Answer 1

The average atomic mass of boron is 10.8 amu, which is calculated by taking into account the isotopic composition of boron-10 (19.90%) and boron-11 (80.10%). The correct option is (A).

Step-by-step explanation:

The average atomic mass of boron can be calculated using the percentage abundances of its isotopes. By multiplying the mass of each isotope by its relative abundance and then summing these values, we can find the overall average atomic mass.

To calculate the average atomic mass for boron in this case:

(19.90% × 10 amu for boron-10) + (80.10% × 11 amu for boron-11)

= (0.1990 × 10) + (0.8010 × 11)

= 1.990 + 8.811

= 10.801 amu

Therefore, the mass of an average boron atom, and thus boron's atomic mass, is 10.8 amu. It's important to note that this is an average value as individual boron atoms can weigh either approximately 10 amu or 11 amu.