Boron has an average atomic mass of 10.81. One isotope of boron has a mass of 10.012938 and a relative abundance of 19.80 percent. The other isotope has a relative abundance of 80.20 percent what is the mass of that isotope? Report two decimal places

Answer: The atomic mass of the second isotope of boron (B) is 11.01 amu.

Explanation:

The average atomic mass is can be calculated by the summation of the product of the atomic mass of each isotope multiplied by its abundance (abundance % / 100.0). Boron has two isotopes:

1) At. mass = 10.012938 amu ≅ 10.013 amu and its abundance = 0.198

2) At. mass = ? amu and its abundance = 0.802

Average atomic mass of boron = 10.81 amu.

The average atomic mass of boron = (10.013 amu) * (0.198) + (atomic mass of the second isotope amu) * (0.802) = 10.81 amu 10.81 = 1.9825 + (0.802 x atomic mass of the second isotope) (0.802 x atomic mass of the second isotope) = 10.81 - 1.9825 = 8.8275. Atomic mass of the second isotope = 8.8275 / 0.802 = 11.0068 ≅ 11.01 amu.