Average atomic mass?

Question

A certain element X forms a compound with oxygen in which there are two atoms of X for every three atoms of oxygen. In this compound, 2.09 g of X are combined with 0.720 of oxygen.


Use the average atomic mass of oxygen to calculate the average atomic mass of X.

Answer 1

0.72 g corresponds to 0.045 moles of O

Thus 0.03 moles of X weigh 2.09 g.

The at mass of X is 69.6 g.