Help! Hydrogen peroxide volume / concentration

I am writing up my A2 Chemistry Investigation for OCR Salters. I was given hydrogen peroxide labelled with 5 vol. The thing is I need to work out the concentration of hydrogen peroxide I used in the reaction mixture of an experiment I am doing. I've been told that 1 volume is approximately 0.1 mol dm^-3. Is this correct? If it is then I can just say that my stock solution of hydrogen peroxide is 0.5 mol dm^-3.

Sorry but I don't understand why hydrogen perxide was given to me in "vol" and I don't know anything about volume. Any help would be appreciated.

The vol measure used in hydrogen peroxide refers to the volume of oxygen that it produces per volume of hydrogen peroxide used up at room temperature.

So, if you consider the equation:

2H₂O₂ --> 2H₂O + O₂

You can see that 2 moles of hydrogen peroxide produces 1 mole of oxygen, i.e. the number of moles of oxygen produced is half that of hydrogen peroxide used up.

If your hydrogen peroxide solution is 100 vol (quite reasonable for a strong stock solution) this means that 1000 cm3 of the H₂O₂ produces 100,000 cm3 of oxygen.

100 dm3 of oxygen = 100/24 moles = 4.17 moles

If 4.17 moles of oxygen are produced then there must have been 4.17 x 2 moles of hydrogen peroxide = 8.34 moles in 1 dm3 = 8.34 molar.

so if 100 vol is 8.34 molar then 1 vol = 0.0834 molar etc.