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Topic: How many moles of C,H and O were in the sample?  (Read 8687 times)

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Offline luketapis

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How many moles of C,H and O were in the sample?
« on: November 29, 2011, 07:52:52 PM »
An unknown compound contains only carbon, hydrogen, and oxygen (CHO). Combustion of 5.00 g of this compound produced 7.33 g of carbon dioxide and 3.00 g of water. How many moles of C,H and O were in the sample? How to understand that?

         CH + O2 = CO2+ H2O
mass:  5g     ?                      7.33g              3g
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Offline fledarmus

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Re: How many moles of C,H and O were in the sample?
« Reply #1 on: November 29, 2011, 08:55:36 PM »
Quote from: luketapis on November 29, 2011, 07:52:52 PM
An unknown compound contains only carbon, hydrogen, and oxygen (CHO). Combustion of 5.00 g of this compound produced 7.33 g of carbon dioxide and 3.00 g of water. How many moles of C,H and O were in the sample? How to understand that?

         CHO + O2 = CO2+ H2O
mass:  5g     ?                      7.33g              3g

Just made one little correction in your formula, so you don't forget  ;)

Okay, you've got your reaction and some numbers - do you have any way of relating the number of atoms on one side of the reaction to the number of atoms on the other?

And what form would you expect your answer to be in?
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Offline luketapis

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Re: How many moles of C,H and O were in the sample?
« Reply #2 on: December 10, 2011, 08:05:19 PM »
now there are ratio 5:6 atoms
Do I need to count how many moles is 5g of CHO?
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Offline UG

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Re: How many moles of C,H and O were in the sample?
« Reply #3 on: December 11, 2011, 03:33:03 AM »
How many moles of CO2 was produced? All of the carbon in the unknown compound must have been converted into CO2. Similarly, how many moles of water was produced? All of the hydrogen in the unknown compound must have been converted into H2O. Now you can calculate the mass of carbon and hydrogen in the 5 g sample. The remaining mass left over must be due to oxygen, you can then calculate moles of oxygen.
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Offline Borek

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Re: How many moles of C,H and O were in the sample?
« Reply #4 on: December 11, 2011, 04:20:00 AM »
Quote from: luketapis on December 10, 2011, 08:05:19 PM
Do I need to count how many moles is 5g of CHO?

You can't - you don't know formula nor molar mass, CHO is not a formula, just a list of atoms present.

All you can do is to find out ratios of moles of elements present in the substance, using information about reaction products.
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Offline Hunter2

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Re: How many moles of C,H and O were in the sample?
« Reply #5 on: December 11, 2011, 08:13:45 AM »
CO2 reflects to C and H2O reflects to H

With the given mass calculate the moles of CO2 and H2O and you know them from C and H.

With this knowledge you know at least the mole of the unknown substance. You can calculate back the molecular weight of this substance.

You can substract the molecular weights of carbon and hydrogen and will find the molecular weight from oxygen.

Edit: don't give final answers.
« Last Edit: December 11, 2011, 08:36:33 AM by Borek »
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