Question

If you burn 43.5 g of hydrogen and produce 389 g of water, how much oxygen reacted?

Answer 1

Moles of H2 = 43.5 g / 2 g /mol    = 21.75 mol H2

Moles of water = 389 g / 18 g/mol     = 21.61 mol water.

Balanced equation for water from H2 and O2 is

2 H2 + O2 ----> 2 H2O

1 mole of O2 is reacted to produce two moles of water.

Hence,  moles of O2 required will be half of the moles of water = 21.61 mol/2 = 10.8 moles of O2

Mass of the O2 = 10.8 mol x 32 g/mol = 345.77g

Amount of oxygen reacted = 345.78 g