Chemical Equations: Mass/Mass Calculations

Question

According to the following reaction, how many grams of hydrogen peroxide (H₂O₂) are needed to form 26.3 grams of oxygen gas?

hydrogen peroxide (H₂O₂) (aq) water (l) + oxygen (g)

 grams hydrogen peroxide (H₂O₂)

Answer 1

2 H₂O₂(aq) ==> 2 H₂O + O₂ ... balanced equation

Use dimensional analysis and the stoichiometry of the balanced equation to answer the question:

26.3 g O₂ x 1 mol O₂/32 g x 2 mol H₂O₂ / 1 mol O₂ x 34 g H₂O₂/mol H₂O₂ = 55.9 g H₂O₂ (3 sig. figs.)

Answer 2

The reaction is 2H₂O₂=2H₂O+O₂

The molar mass of H₂O₂ is 34 g/mol

The molar mass of O₂ is 32 g/mol

The mass ratio of H₂O₂/O₂=2*34/32=2.125

26.3g O₂ needs H₂O₂ 26.3*2.125=55.89 g