Question

Boron has two naturally-ocurring isotopes. Boron-10 has an abundance of 19.8% and actual mass of 10.013 amu, and boron-11 has an abundance of 80.2% and actual mass of 11.009 amu. What is the average atomic mass for all isotopes of boron?

Answer 1

Answer:

10.812  to the nearest thousandth,.

Explanation:

That would be 0.198 * 10.013 + 0.802 * 11.009

= 10.812.

Answer 2

Answer:

Average atomic mass = 10.812 amu

Explanation:

The formula for the calculation of the average atomic mass is:

$Average\ atomic\ mass=(\frac {\%\ of\ the\ first\ isotope}{100}\times {Mass\ of\ the\ first\ isotope})+(\frac {\%\ of\ the\ second\ isotope}{100}\times {Mass\ of\ the\ second\ isotope})$

Given that:

For first isotope, Boron-10:

% = 19.8 %

Mass = 10.013 amu

For second isotope, Boron-11:

% = 80.2 %

Mass = 11.009 amu

Thus,  

$Average\ atomic\ mass=\frac{19.8}{100}\times {10.013}+\frac{80.2}{100}\times {11.009}=1.982574+8.829218=10.811792$

Average atomic mass = 10.812 amu