Got a question about empirical formulas...not a hard question, but I could sure use an explanation! Help!?

Question

An amount of Chlorine gas weighs 5.67g and reacts with 8.90 g Oxygen to form a compound. What is the empirical formula?

Ok is the stuff with the grams there to throw me off? Isn't the empirical formula just Cl2O? What's with this question?

Answer 1

5.67 g Cl2 gas. 0.160mol Cl atoms.

8.90 g O2; 0.556 mol O atoms.

Atom ratio, which is what counts for empirical formula, Cl:O :: 1.3.48, near enough 1:3.5

The empirical formula isn't Cl2O. It does correspond to a known (and dangerously reactive) oxide of chlorine.