Question

FIND THE WEIGHT OF 0.2 MOLES OF AGNO3

Answer 1

The abundance of 168O is 99.762 %, and the abundance of 188O is 0.201 %.

Assume you have 100 000 atoms of O. Then you have 37 atoms of 178O and 99 963 atoms of the other isotopes.

Let x = the number of atoms of 168O. Then the number of atoms of 188O = 99 963 - 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 168O or 99.762 %.

The number of 188O atoms is 99 963 – 99 762 = 201 atoms or 0.201 %.

Hope this helps.