Question

A new element has three isotopes. Seventy-five percent of the new element is the first isotope which has a mass of 210 amu. Twenty percent is the second isotope which has a mass of 205 amu. The remaining five percent is third isotope which has a mass of 211 amu. What would be the average atomic mass listed on the periodic table?

Answer 1

Answer: 209.05 amu

Step-by-step explanation:

To calculate the average atomic mass, multiply each mass by its percentage, then add them together.

The first isotope has a mass of 210 amu and a relative abundance of 75%. So, we calculate: 0.75(210) = 157.5

The second isotope has a mass of 205 amu and a relative abundance of 20%. We calculate 0.20(205) = 41.0

The third and last isotope has a mass of 211 amu and a relative abundance of 5%. We calculate 0.05(211) = 10.55

Assuming all numbers are exact and adding them all together:

157.5 + 41.0 + 10.55 = 209.05