# Oxygen is composed of three isotopes 16/8 O (15.995 u), 17/8 O (16.999 u) and 18/8 O (17.999 u). One of these isotopes, 17/8 O, comprises of 0.037% of oxygen. What is the percentage abundance of the other two isotopes, using the average atomic mass of 15.9994 u.

##### 1 Answer

Jun 23, 2014

The abundance of

Assume you have 100 000 atoms of O. Then you have 37 atoms of

Let *x* = the number of atoms of *x*

The total mass of 100 000 atoms is

*x* × 15.995 u + (99 963 – *x*) × 17.999 u + 37 × 16.999 u = 100 000 × 15.9994 u

15.995 *x* + 1 799 234.037 – 17.999 *x* + 628.963 = 1 599 940

2.004 *x* = 199 123

*x* = 199 123/2.004 = 99 762

So there are 99 762 atoms of

The number of

Hope this helps.