Question

The astronaut then measures the abundance of strontium on the new planet, obtaining the following results:
Isotope Abundance
(%) Mass
(amu)
86Sr 9.46 85.91
87Sr
7.00 86.91
88Sr 83.54 87.91
What is the atomic mass of strontium for this planet?

Answer 1

Atomic mass is equal to the average number allowing for the relative abundances of different isotopes. It is calculated by:

Atomic mass = ΣzₓAₓ 

where zₓ is the relative abundance of the isotope and Aₓ is the atomic mass of the isotope.

Atomic mass = (0.0946x85.91) + (0.07x86.91) + (0.8354x87.91) = 87.6508 amu