How Many Moles of Oxygen Gas Are Produced from Decomposing Hydrogen Peroxide?

[chakakhan]

Homework Statement

Calculate the number of moles of oxygen gas produced from the completely catalyzed decomposition of 6.60ml sample of a 3.5% solution of H2O2. The density of the 3.5% solution of H2O2 is 1.01 g/ml.

Homework Equations

2(H2O2) --> 2(H2O) + O2
p=m/v

The Attempt at a Solution

I used. 1.01g/ml=m/6.6ml to get 6.1206g of the solution
Multiplied 6.1206 by .035 to get .214221g H2O2
.214221g H2O2(1mol H2O2/18.016g H202)(2 mol O/2mol H2O2)(16g O/1 mol O) yields .1897g O
.1897g O (1 mol O/16g O) yields .0118 mol O. This answer was rejected. I even tried .0236 since the equation shows O2, just to be sure. Wrong as well.

 

[phyzguy]

If O is 16 g/mole, and H is 1 g/mole then H2O2 is ? g/mole? Not 18.016.

 

[chakakhan]

Right, I caught that. It should be 34.016g. I ran the same calculations with that number, but to no avail.
There was also actually 6.666g of solution, but what I've tried with that number is still wrong.

 

[Borek]

Please show your results now - there are several problems with the way you calculated amount of oxygen, but as you corrected some of them it is not clear what is the current version of your calculations, so it is not possible to check it.

Moles of oxygen gas means moles of O₂. But

.0118 mol O. This answer was rejected. I even tried .0236 since the equation shows O2

this is wrong - 0.0118 mol of atomic O is not equivalent to 0.0236 moles of O₂.

It is also possible system rejects answer that is technically correct, but has wrong number of significant digits.

 

[DeeNos]

I would first check my calculations to ensure they are correct. It appears that there is a mistake in the conversion from grams of H2O2 to moles of O2. The correct calculation should be:

0.214221g H2O2 (1mol H2O2/34.0147g H2O2) (2 mol O2/2 mol H2O2) (32g O2/1 mol O2) = 0.012 mol O2

Therefore, the number of moles of oxygen gas produced from the decomposition of the 6.60ml sample of 3.5% H2O2 solution is 0.012 moles. It is important to always double check calculations and units to ensure accurate results.