[anon163]

hi, i'm a chemistry a-level student and i am currently working on the ideal gas equation, i have been given a question to do with this and i am stuck, i do not know what other formulas i need etc (Where to start) plz help. the question is-->

calculate the volume of oxygen produced at 298K and 100KPa by a decomposition of 30cm(cubed) of 0.1 moldm(-3) of hydrogen peroxide.

i have also been given the equation  :rarrow:2H(2)O(2)(aq) 2(H2O) (l) + O2(g)
i know that PV=nRT MUST COME IN SOMEWHERE...

your help would be very much apreciated. thnx
sorry about all the bad grammar

[anon163]

using pv=nrt to work out the volume of hydrogen peroxide i got:
where:
 p= 100000
n= c/v*1000 = 0.1*30/1000 = 0.003
r = 8.31 ( gas constant)
t = 298k
the v is 7.42914*10^-5 m^3
how do i work out oxygen from this?

[Borek]

pV=nRT is ideal GAS equation, hydrogen peroxide is a liquid, dissolved in water.

How many moles of hydrogen peroxide?

How many moles of oxygen will be produced?

[anon163]

i worked out the no. of moles of h2o2 as 0.003 but i am not sure and not very clear on how to work out the amount of o2 from this
n= c/v*1000 = 0.1*30/1000 = 0.003

[Borek]

Simple stoichiometry - you are given reaction equation.

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations

[anon163]

so the moles of oxygen will be 0.003/68*32? =0.0041176....
0.0041176/0.1 =0.01411...dm-3. is this correct or am i doin it wrong?

[sjb]

so the moles of oxygen will be 0.003/68*32? =0.0041176....
0.0041176/0.1 =0.01411...dm-3. is this correct or am i doin it wrong?

No, you do not need the molecular weights here. (and the calculation is not right, in any regard 0.003 / 68 * 32 approximately equals 0.003 / 2, or less than 0.003, not more)

2H₂O₂(aq)  2H₂O (l) + O₂(g) implies 2 moles (or 2 molecules, 2 dozen, 2 gross...) of hydrogen peroxide form 1 mol of oxygen, so how many moles of oxygen are formed with 0.003 mol peroxide?

[anon163]

0.0015moles
vol no. of moles / molar concentration, is molar concentration just the same  0.1?

[sjb]

OK, so you now have p, n, R and T; can you rearrange the ideal gas equation to solve for V ?

[anon163]

v=nrt/p
v=0.0015*8.31*298
              100000
= 0.00003714...m^3

thank you, i was getting cofused with all the formulas and finding which 2 use

[sjb]

Are you sure you're using the right value for R? This seems very low - what are the units for R in your equation?

[Borek]

No, that's OK - he gave the answer in m³.

[sjb]

No, that's OK - he gave the answer in m³.

My bad, miscounted the number of 0's