Question

In nature, oxygen has three common isotopes. The atomic masses and relative abundances of these isotopes are given in the table below. Isotope Atomic Mass (amu) Relative Abundance O-16 15.995 99.759% O-17 16.995 0.037% O-18 17.999 0.204% Calculate the average atomic mass of oxygen. Show all of your calculations below.

Answer 1

Answer: The average atomic mass of oxygen is 15.999 amu

Explanation:

Mass of isotope O-16 = 15.995 amu

% abundance of isotope O-16= 99.759 % = $\frac{99.759}{100}=0.99759$

Mass of isotope O-17 = 16.995 amu

% abundance of isotope O-17 = 0.037% = $\frac{0.037}{100}=0.00037$

Mass of isotope O-18 = 17.999 amu

% abundance of isotope O-18 = 0.204% = $\frac{0.204}{100}=0.00204$

Formula used for average atomic mass of an element :

$\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})$

$A=\sum[(15.995\times 0.99759)+(16.995\times 0.00037)+(17.999 \times 0.00204)]$

$A=15.999$

Thus the average atomic mass of oxygen is 15.999 amu