Question

A certain element (X) has isotopes with mass numbers of 10 and 11. The X-10 isotope has an atomic mass of 10.013, and it represents 19.9% of all atoms of this element. The X-11 isotope has an atomic mass of 11.009, and it represents 80.1% of all atoms of this element. Therefore, the average atomic mass, or atomic weight, of this element is amu.

Answer 1

`m=10.811 amu`

Step-by-step explanation:

The average atomic mass in amu is calculated using the following formula

`m=((m_(1) \%m_(1))+(m_(2) \%m_(2)))/(100 \%)`

`m_(1)= 10.013\\ \%m_(1)= 19.9\%(abundance)\\ m_(2)= 11.009\\ \%m_(2)= 80.1\%(abundance)`

`m=(((10.013).(19.9\%))+((11.009) (80.1\%)))/(100 \%)\\ m=10.811 amu`

Answer 2

The average atomic mass of element X is 10.81 u.

The average atomic mass of X is the weighted average of the atomic masses of its isotopes.

We multiply the atomic mass of each isotope by a number representing its relative importance (i.e., its % abundance).

Thus,

0.199 × 10.013 u = 1.993 u

0.801 × 11.009 u = 8.818 u

TOTAL = 10.81 u