chemistry question

Question

If 200.8 g of carbon dioxide gas is made from the complete combustion of isopropanol (C₃H₇OH), how many moles of oxygen are used up?

Answer 1

2C₃H₇OH + 9O₂ ==> 6CO₂ + 8H₂O ... balanced equation for combustion of C3H₇OH

moles CO₂ formed = 200.8 g CO₂ x 1 mol CO₂/44 g = 4.56 moles CO₂ formed

moles of O₂ used = 4.56 moles CO₂ x 9 moles O₂ / 6 moles CO₂ = 6.85 moles O₂ used