The Student Room Group
Reply 1
It seems impossible, could anyone shed some light on the question?
Reply 2
Crabman
It seems impossible, could anyone shed some light on the question?
Do empirical formula to find the ratio, then scale up to find the actual formula with RFM of 60
Reply 3
Well if it is organic and produces CO2 and H2O when combusted. Assume that it only contains C, H and O. The ratios of the products should give you the formula. Sorry I can't give any more info on it
Reply 4
0.733/(12x2 + 16) 0.3/(16+2)
Reply 5
lanky2610
Well if it is organic and produces CO2 and H2O when combusted. Assume that it only contains C, H and O. The ratios of the products should give you the formula. Sorry I can't give any more info on it



It might just contain C and H though.
Consider:

CxHyOz + nO2 ---> x(CO2) + 2y(H2O)
CHEM1STRY
It might just contain C and H though.


Not if it's products are carbon dioxide and water.
Meteorshower
Not if it's products are carbon dioxide and water.


hydrocarbons combust in oxygen to give CO2 and H2O?
Reply 9
Meteorshower
Not if it's products are carbon dioxide and water.


But isn't methane:

CH4 (g) + 2 O2 (g) --> CO2 (g) + 2 H2O

Hydrocarbons combust for CO2 and H2O
EierVonSatan
hydrocarbons combust in oxygen to give CO2 and H2O?


Sorry don't know what I was thinking there XD

Ignore my previous post everyone :tongue:
Meteorshower
Sorry don't know what I was thinking there XD


It's ok. I guess we have to consider both possibilities?
0.733g and 0.3g seem rather odd numbers. C2H4O2 and C3H8O both have masses of 60, but give twice the mass of CO2 than water.
Reply 13
That's exactly what I was thinking pigetrational.


Maybe there is some triple bonds that need to be considered?


What level are we talking A-Level?


All I've got so far is (i've used fractions to keep it in exact form)

You start with 0.5g of X which has an Mr of 60, so you've got 1/120 mols of X.

And you end up with 3/440 mols of CO2
and 733/18000 mols of H2O


from there I have no idea.
Reply 14
i just worked it out, is the answer C2H402
Reply 15
moles CO2 is 0.733/44=0.0167
moles H20 is 0.3/18=0.016
Mrxn=m
mass of Carbon=12x0.0167
mass Hydrogen = 2x0.016
add up ansswers and minus from 0.5 to get mass of oxygen, and then simply do empirical formula and you will have to multiply by 2 as you wil get CH20, which has Mr 30
Yeh that's what I got it as: C2H4O2.
Alternatively, consider the reaction:
C2H4O2 + 2O2 --> 2CO2 + 2H2O, so therefore 1 mole of C2H4O2 makes 2 moles of CO2.
Therefore, 0.5g of X is 1/120 of a mole, so it would make 1/60 mole of CO2.
Multiply by Mr of CO2 (44) to get 0.7333g
Oh, just worked it out. Got C2H4O2 via the same method as palacefc8.
Reply 19
thanks everyone!

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