How many atoms of oxygen are in 3.47 liters of oxygen gas at STP?

Question

anonymous · Answer

I'm a AP chemistry student, and this one is going to send me through the roof. In order to get credit for this question, I'm supposed to get 1.87E23 atoms of O2; here's what I got:

3.47L O2 | 1 mol O2/22.4L O2 | 6.02E23 atoms O2/1 mol O2 == 9.33E22 atoms O2.

The teacher also told the student I'm tutoring that he's missing a step; either I'm overlooking something or the teacher made a mistake. Regardless I just want to figure this one out!