Question

If you burn 53.8 g of hydrogen and produce 481 g of water, how much oxygen reacted?

Answer 1

The reaction:
2 H 2 + O 2 → 2 H 2 O
2 Hydrogen molecules react with 1 Oxygen molecule to create 2 molecules of water. 
We have to convert 53.8 g of Hydrogen into moles:
53.8 : 2.02 g / moles = 26.63 moles
2 moles H 2 ↔ 1 mole O 2
26.63 moles H 2  ↔ 13.32 moles O 2
Mass ( O 2 ) = 13.32 moles · 32 g/moles = 426.2 g
Answer: 426.2 grams of Oxygen.