Question

A certain element exists as two different isotopes. 90.50% of its atoms have a mass of 20.00 amu and 9.500% of its atoms have a mass of 22.00 amu. What is the average atomic mass of this element? (Do not round your answer)

Answer 1

20.19 amu.

Step-by-step explanation:

From the question given above, the following data were obtained:

Isotope A:

Abundance (A%) = 90.5%

Mass of A = 20 amu

Isotope B:

Abundance (B%) = 9.5%

Mass of B = 22 amu

Average atomic mass =..?

The average atomic mass of the element can be obtained as follow:

Average atomic mass = [(Mass of A × A%)/100] + [(Mass of B × B%)/100]

Average atomic mass = [(20 × 90.5)/100] + [(22 × 9.5)/100]

Average atomic mass = 18.1 + 2.09

Average atomic mass = 20.19 amu

Therefore, the average atomic mass of the element is 20.19 amu