Hydrogen peroxide, H2O2, decomposes to produce water and oxygen as in the following equation: 2 H2 O2(l) ⎯→ 2H2O(l) + O2(g)

Question

What would be the volume of O2 released from the decomposition of 250 mL of 2.0 M H2O2 at

STP?

Answer 1

Hello, Sarah,

2H₂O₂ = 2H₂O + 1O₂

The balanced equation tells us that we'll obtain 1 mole of O₂ for every 2 moles of H₂O₂, a molar ratio of 0.5 O₂/H₂O₂ .

Find the moles of H₂O₂: (0.250L)*(2.0 moles H₂O₂/L) = 0.50 moles H₂O₂

[M is the abbreviation for moles/liter]

Therefore we have (0.50 moles H₂O₂)*(0.5 moles O₂/moles H₂O₂ ) = 0.25 moles O₂

All gases occupy 22.4 liters/mole at STP. We can use this as a conversion factor.

(0.25 moles O₂)*(22.4 liters/mole O₂) = 5.6 liters O₂

Wow - sounds like a lot of oxygen for only having started with 250 ml of hydrogen peroxide, but the difference in densities should explain the difference.

Bob