Question

How many milliliters of O2 are consumed in the complete combustion of a sample of hexane, C6H14, if the reaction produces 325 mL of CO2? Assume all gas volumes are measured at the same temperature and pressure. The reaction is
2C6H14(g) + 19O2(g) -> 12CO2(g) + 14H2O(g)

Answer 1

When it's an all gas sample and the T and P don't change, you may use a shortcut and use volume directly as if they were mols.
2C6H14(g) + 19O2(g) -> 12CO2(g) + 14H2O(g)

325 mL CO2 x (19 mols O2/12 mols CO2) = 325 mL x (19/12) = mL O2 consumed.

Answer 2

Around 514.58?

Answer 3

Yes, and if your prof is picky about the number of significant figures you whould round that to 514 mL. You are limited to 3 from the 325 to start.