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TrojanPoem

  • one year ago

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.

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  1. phi
    • one year ago
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    How far did you get ?

  2. Michele_Laino
    • one year ago
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    from your data, we can see that the ratio: water vapor and carbon dioxide =0.3618/ 0.762= 1/2 (approximated value)

  3. TrojanPoem
    • one year ago
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    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.

  4. TrojanPoem
    • one year ago
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    I meant equal or less if equal -> Only H , C if less H, C, other elements

  5. phi
    • one year ago
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    I assume the O comes from the air, and the organic compound does not contain O ?

  6. TrojanPoem
    • one year ago
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    Maybe and maybe it was C2H5OH or something else with O

  7. TrojanPoem
    • one year ago
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    But I think you are right Phi, the O comes from the air as 0.3618 + 0.762 (not equal to) 0.4122

  8. TrojanPoem
    • one year ago
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    if so the mass of (O) = 0.3618 + 0.762 - 0.4122 = 0.7116 grams

  9. phi
    • one year ago
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    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 ?

  10. TrojanPoem
    • one year ago
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    Yeah.

  11. TrojanPoem
    • one year ago
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    The problem already asks about ashes ( other elements) in the next part (2).

  12. phi
    • one year ago
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    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

  13. TrojanPoem
    • one year ago
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    |dw:1435431964444:dw|

  14. TrojanPoem
    • one year ago
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    Like 0.21 grams

  15. TrojanPoem
    • one year ago
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    so oxygen in Co2 = 0.762 - 0.21 = 0.552

  16. TrojanPoem
    • one year ago
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    Hmm phi am I mistaken ?

  17. phi
    • one year ago
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    sounds right. But the question is Find the percentage of carbon and hydrogen in the compound.

  18. phi
    • one year ago
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    How do they measure percentage? By weight? or fractions of atoms?

  19. TrojanPoem
    • one year ago
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    Mass of Carbon ( H only) / Mass of compound (C,H)

  20. TrojanPoem
    • one year ago
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    Like normal percentages in maths

  21. phi
    • one year ago
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    so %C is 0.21 grams / 0.4122

  22. TrojanPoem
    • one year ago
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    Yea , = 50.94 % ( 0.21/0.4122 times 100)

  23. phi
    • one year ago
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    now do the H

  24. TrojanPoem
    • one year ago
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    |dw:1435432795512:dw|

  25. TrojanPoem
    • one year ago
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    wait it's 0.292 so the compound contains other elements

  26. phi
    • one year ago
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    %H is about 0.0804/0.4122

  27. phi
    • one year ago
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    H + C add up to about 70% of the weight of the compound 30% must be something else.

  28. TrojanPoem
    • one year ago
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    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) =

  29. phi
    • one year ago
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    could be. plus other stuff. I think you need more info.

  30. TrojanPoem
    • one year ago
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    Like ?

  31. phi
    • one year ago
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    I'm not a chemist.

  32. TrojanPoem
    • one year ago
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    I mean is the reasoning enough ( in your opinion ) ?

  33. phi
    • one year ago
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    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.

  34. TrojanPoem
    • one year ago
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    Thanks for the help @phi.

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