Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: anon163 on October 13, 2009, 01:13:22 PM

Title: volume of gas from solution *(plz help me)
Post by: anon163 on October 13, 2009, 01:13:22 PM
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) :rarrow: 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
Title: Re: volume of gas from solution *(plz help me)
Post by: anon163 on October 13, 2009, 01:31:10 PM
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?
Title: Re: volume of gas from solution *(plz help me)
Post by: Borek on October 13, 2009, 01:38:36 PM
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?
Title: Re: volume of gas from solution *(plz help me)
Post by: anon163 on October 13, 2009, 01:42:23 PM
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
Title: Re: volume of gas from solution *(plz help me)
Post by: Borek on October 13, 2009, 02:15:37 PM
Simple stoichiometry - you are given reaction equation.

http://www.chembuddy.com/?left=balancing-stoichiometry&right=stoichiometric-calculations
Title: Re: volume of gas from solution *(plz help me)
Post by: anon163 on October 13, 2009, 02:24:38 PM
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?
Title: Re: volume of gas from solution *(plz help me)
Post by: sjb on October 13, 2009, 02:43:53 PM
Quote from: anon163 on October 13, 2009, 02:24:38 PM
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)  :rarrow: 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?
Title: Re: volume of gas from solution *(plz help me)
Post by: anon163 on October 13, 2009, 02:47:29 PM
0.0015moles
vol no. of moles / molar concentration, is molar concentration just the same  :rarrow: 0.1?
Title: Re: volume of gas from solution *(plz help me)
Post by: sjb on October 13, 2009, 02:49:08 PM
OK, so you now have p, n, R and T; can you rearrange the ideal gas equation to solve for V ?
Title: Re: volume of gas from solution *(plz help me)
Post by: anon163 on October 13, 2009, 02:58:01 PM
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
Title: Re: volume of gas from solution *(plz help me)
Post by: sjb on October 13, 2009, 03:20:26 PM
Are you sure you're using the right value for R? This seems very low - what are the units for R in your equation?
Title: Re: volume of gas from solution *(plz help me)
Post by: Borek on October 13, 2009, 05:55:58 PM
No, that's OK - he gave the answer in m3.
Title: Re: volume of gas from solution *(plz help me)
Post by: sjb on October 14, 2009, 02:25:44 PM
Quote from: Borek on October 13, 2009, 05:55:58 PM
No, that's OK - he gave the answer in m3.

My bad, miscounted the number of 0's :(