Question

PLEASE EXPLAIN WHAT U DID FOR THE ANSWER

Answer 1

Answer: 12.18 u

Explanation:

The average atomic mass of an element is calculated by taking the weighted average of the atomic masses of its stable isotopes.

In other words, each stable isotope will contribute to the average mass of the element proportionally to its abundance.

avg. atomic mass

=

∑

i

(

isotope

i

×

abundance

i

)

To calculate an isotope's decimal abundance, you need to divide the number of atoms of that isotope by the total number of atoms present in the sample.

In your case, you know that the sample contains

100

atoms with an atomic mass of

12.00 u

and

10

atoms with an atomic mass of

14.00 u

.

The total number of atoms in the sample will thus be

100

+

10

=

110 atoms

The decimal abundances for the two isotopes will be

100

atoms

110

atoms

=

0.90909

→

for the first isotope

10

atoms

110

atoms

=

0.090909

→

for the second isotope

This means that the average atomic mass of the element will be equal to

avg atomic mas

=

12.00 u

×

0.90909

+

14.00 u

×

0.090909

avg. atomic mass

=

12.18181 u

I think I'll leave this rounded off to four sig figs, the number of sig figs you have for the atomic masses of the two isotopes

avg. atomic mass

=

12.18 u

Hope this helps! :)