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Offline JZ_1

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problem with hydrocarbons
« on: July 20, 2005, 02:48:55 PM »
Here is the statement:
   It states that there is a hydrocarbon with an emprical formula CH and it contains 0.923 g of carbon per gram of hydrocarbon.

Here is the question:
   Calculate the mass of H that combines with 1 g of C.

--I don't REALLY have an idea how to go about solving --

Here is what i first did:
   1g C X (1g Hydrocarbon/0.923g C)
          [that will cancel out the "grams per Carbon"]
     giving me....approx.= 1.08 g HYDROCARBON
AS the question says, i need the mass of hydrogen NOT hydrocarbon.....i'm stuck here

Here are some notes:
   I dont know if these help..

    I found only 2 different formulas with the emprical formula CH

They are:        
   • 1,2,3-Butene
   • 1-Ethyne

Here's the problem:
   I dont even know what i tried to solve is right or not...and if so, how to continue from there....Thx
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Offline Borek

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Re:problem with hydrocarbons
« Reply #1 on: July 20, 2005, 03:16:51 PM »
Quote from: JZ_1 on July 20, 2005, 02:48:55 PM
hydrocarbon with an emprical formula CH and it contains 0.923 g of carbon per gram of hydrocarbon.

That's tautology.

Quote
giving me....approx.= 1.08 g HYDROCARBON

Mass of hydrocarbon is mass of carbon plus mass of hydrogen.
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Offline JZ_1

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Re:problem with hydrocarbons
« Reply #2 on: July 20, 2005, 04:40:56 PM »
I dunno if this will help anyone help me..itz in the book
§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§
  HYDROCARBON -- GRAMS OF C PER GRAMS OF HYDROC
    methane         -    0.750
    ethylene          -    0.857
    ethane             -   0.800
    propane           -   0.818
    butane             -   0.828

AS U CAN SEE...ethylene is a little heavier than ethane ...
...it could still be either ethyne of butene..
????????


itz tautology because I multiplied it...i dont think that answer is corresponding to what the question is asking...because i need the MASS OF H PER 1 GRAM OF C, and NOT GRAMS OF HYDROCARBON PER 1 GRAM OF C

since i have the mass of the hydrocarbon per gram of Carbon....how do i sepparate the the hydrocarbon into hydrogen and carbon?
I dont know the real formula!!!!!!!!
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Offline Borek

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Re:problem with hydrocarbons
« Reply #3 on: July 20, 2005, 05:11:33 PM »
Quote from: JZ_1 on July 20, 2005, 04:40:56 PM
...it could still be either ethyne of butene..

No, it can be anything with formula CnHn. Like

HC?C-CH2-(CH=CH)m-CH2-C?CH

Quote
I dont know the real formula!!!!!!!!

And you don't need it. CH means for every 12g of carbon there is 1g of hydrogen and they together create 13g of hydrocarbon. Thus mass fraction of carbon is 12/13=0.923 - so CH and 0.923g of carbon per 1g of hydrocarbon are exactly the same information.

As I told you: mass of hydrocarbon is mass of carbon plus mass of hydrogen.
« Last Edit: July 20, 2005, 05:20:42 PM by Borek »
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Offline JZ_1

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Re:problem with hydrocarbons
« Reply #4 on: July 21, 2005, 01:08:30 PM »
yea..i was about to get there..

since 1.08 - 1.01 = (0.07g of H/1 gram of C)....it is a little off with the matth and the sig figs...should i write 0.07 and do the math the way i started?...Or should i write 0.08 as the answer with the following as work i did:
      1.01/12.01 = 0.08g H/1g C

thx for your time...i'll find a way to delete these posts
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Offline jdurg

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Re:problem with hydrocarbons
« Reply #5 on: July 22, 2005, 09:20:07 AM »
This is actually a VERY simple ratio problem.  The initial problem says that for every gram of hydrocarbon you have 0.923 grams of carbon.  Therefore, for every gram of hydrocarbon you have 1-0.923 grams of hydrogen.  So you can set up an easy ratio of 0.923 g C/.077 g H is equal to 1 g C/x g H.  Just solve for H.

For the significant figures, that's a bit of a doozy there as the initial question says 1 g of Carbon.  That would limit you to just one significant figure which seems a bit preposterous.  So I would limit my significant figures to three digits and three decimal places.  I would come out with an answer of 8.34x10-3 grams of Hydrogen.
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Offline JZ_1

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Re:problem with hydrocarbons
« Reply #6 on: July 23, 2005, 06:42:33 PM »
I am now even more confused than before!!!

Quote from: jdurg on July 22, 2005, 09:20:07 AM
For every gram of hydrocarbon you have 1-0.923 grams of hydrogen.

Why the one? in 1-0.923 ?
I have different answers in trying to test what you did on methane

 ???
With borek's thing.
4.0g H/16g CH4 gives me 0.333 or 0.336 which seems to be the answer...

Jdurg, How do i use your ratio thingy on Methane to find that answer?...do i use 4-0.750?
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Offline Borek

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Re:problem with hydrocarbons
« Reply #7 on: July 23, 2005, 07:22:54 PM »
Quote from: JZ_1 on July 23, 2005, 06:42:33 PM
Why the one? in 1-0.923 ?

You were told that 1g of hydrocarbon contains 0.923 g of carbon. 1-0.923 is mass of hydrogen in 1g of hydrocarbon.
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