TrojanPoem
  • TrojanPoem
Question : Help please ! 0.4122 grams of an organic compound was burnt totally , so the weight of the containers of absorbing water vapor and carbon dioxide were increased by 0.3618 grams , 0.762 grams respectively. 1- Find the percentage of carbon and hydrogen in the compound. 2- Is there any other element in the organic compound ? , Giving a reason.
Chemistry
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SOLVED
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katieb
  • katieb
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phi
  • phi
How far did you get ?
Michele_Laino
  • Michele_Laino
from your data, we can see that the ratio: water vapor and carbon dioxide =0.3618/ 0.762= 1/2 (approximated value)
TrojanPoem
  • TrojanPoem
What confuses me is that Organic compound -(burnt)-> nH2o + mCo2 so the sum of their masses must be equal or more to the compound itself but it is more.

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TrojanPoem
  • TrojanPoem
I meant equal or less if equal -> Only H , C if less H, C, other elements
phi
  • phi
I assume the O comes from the air, and the organic compound does not contain O ?
TrojanPoem
  • TrojanPoem
Maybe and maybe it was C2H5OH or something else with O
TrojanPoem
  • TrojanPoem
But I think you are right Phi, the O comes from the air as 0.3618 + 0.762 (not equal to) 0.4122
TrojanPoem
  • TrojanPoem
if so the mass of (O) = 0.3618 + 0.762 - 0.4122 = 0.7116 grams
phi
  • phi
0.4122 grams of an organic compound was burnt totally I would like to know the weight of any solid ash. but you have (CH other stuff) + O= H2O + CO2 (+ ash?) so the total weight of H2O + CO2 - compound is the weight of added O ?
TrojanPoem
  • TrojanPoem
Yeah.
TrojanPoem
  • TrojanPoem
The problem already asks about ashes ( other elements) in the next part (2).
phi
  • phi
my original thought was 2/18 of the H2O represents the H in the compound and 12/44 of the CO2 is the amount of C
TrojanPoem
  • TrojanPoem
|dw:1435431964444:dw|
TrojanPoem
  • TrojanPoem
Like 0.21 grams
TrojanPoem
  • TrojanPoem
so oxygen in Co2 = 0.762 - 0.21 = 0.552
TrojanPoem
  • TrojanPoem
Hmm phi am I mistaken ?
phi
  • phi
sounds right. But the question is Find the percentage of carbon and hydrogen in the compound.
phi
  • phi
How do they measure percentage? By weight? or fractions of atoms?
TrojanPoem
  • TrojanPoem
Mass of Carbon ( H only) / Mass of compound (C,H)
TrojanPoem
  • TrojanPoem
Like normal percentages in maths
phi
  • phi
so %C is 0.21 grams / 0.4122
TrojanPoem
  • TrojanPoem
Yea , = 50.94 % ( 0.21/0.4122 times 100)
phi
  • phi
now do the H
TrojanPoem
  • TrojanPoem
|dw:1435432795512:dw|
TrojanPoem
  • TrojanPoem
wait it's 0.292 so the compound contains other elements
phi
  • phi
%H is about 0.0804/0.4122
phi
  • phi
H + C add up to about 70% of the weight of the compound 30% must be something else.
TrojanPoem
  • TrojanPoem
So maybe it's oxygen. The reason is : There is other elements because the sum of mass of (H) + mass of (C) is less than the mass of the compound so there is other elements and their mass is Compound - mass (h+c) =
phi
  • phi
could be. plus other stuff. I think you need more info.
TrojanPoem
  • TrojanPoem
Like ?
phi
  • phi
I'm not a chemist.
TrojanPoem
  • TrojanPoem
I mean is the reasoning enough ( in your opinion ) ?
phi
  • phi
we know how many grams of H and C were in the original and are now in the CO2 and H2O. If the compound "burned completely", that must be all its C and H (burned completely means every C or H combined with O from the air) We know the C and H account for 70% of the mass of the compound. that leaves 30% of the compound being other elements, including O or whatever.
TrojanPoem
  • TrojanPoem
Thanks for the help @phi.

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