# Question Related To Volume Strength Of H2O2.

CosmicC
1. Question Statement and details : 500 mL of 56V H2O2 is kept in an open container due to which some H2O2 is decomposed and evolves 8gm O2 simultaneously, during the process some H2O also vapourizes.Due to all these changes final volume is reduced by 20%. Find final volume strength of H2O2 (aq).
It's a multiple choice question. Options are as follows
(a.) 56V (b) 44.8 V (c.) 11.2V (d.) 33.6V. Correct Answer is 33.6 V.

2. Homework Equations :
Molarity = Volume strength/11.2 and Normality = Volume Strength , in balanced reaction 1 mol H2O2 gives 1/2 half mol O2. Mol. Wt. H2O2=34.

## The Attempt at a Solution

: [/B]By stoichiometry 1/2 moles of H2O2 gives 1/4 moles of O2. So volume strength of H2O2 used to give 8gm is 22.4*1/4 = 5.6. So I subtracted that from 56V. And then simply reduced what i got by 20% it didn't work though. What i'm getting is 39.6 not close to the answer which is 33.6 V. Please help me out on this one. Thank You.

Borek
Mentor
So volume strength of H2O2 used to give 8gm is 22.4*1/4 = 5.6. So I subtracted that from 56V.

That's not a correct approach. Would you do the same if the initial volume was 1 L? 10 L? Don't you think in each case the concentration change should be different?

CosmicC
That's not a correct approach. Would you do the same if the initial volume was 1 L? 10 L? Don't you think in each case the concentration change should be different?
Thanks for replying i really appreciate it. So what should i do..Can you please ellaborate so that i can get the answer to this as soon as possible. I've already given it too much time.

Borek
Mentor
Do you know what volume strength means?

In general: you have to calculate how much hydrogen peroxide was left and what was the final volume, then use this information to calculate final concentration.