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

Converting the percent abundance into decimal form, we get:

O-16: 99.759% = 99.759/100 = 0.9975

O-17: 0.037% = 0.037/100 = 0.00037

O-18: 0.204% = 0.204/100 = 0.0020

Average atomic mass of oxygen is:

(15.995) x (0.9975) + (16.995) x (0.00037) + (17.999) x (0.0020)

= 15.955 + 0.0062 + 0.0359

= 15.997 amu

Step-by-step explanation:

From PLATO

Answer 2

Answer: The average atomic mass of oxygen is 15.999 amu

Step-by-step explanation:

Mass of isotope O-16 = 15.995 amu

% abundance of isotope O-16= 99.759 % =
`(99.759)/(100)=0.99759`

Mass of isotope O-17 = 16.995 amu

% abundance of isotope O-17 = 0.037% =
`(0.037)/(100)=0.00037`

Mass of isotope O-18 = 17.999 amu

% abundance of isotope O-18 = 0.204% =
`(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}* {{\text { fractional abundance}})`

`A=\sum[(15.995* 0.99759)+(16.995* 0.00037)+(17.999 * 0.00204)]`

`A=15.999`

Thus the average atomic mass of oxygen is 15.999 amu