Hydrocarbons in Combustion

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Erin 2I
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Hydrocarbons in Combustion

Postby Erin 2I » Sat Oct 10, 2015 6:45 pm

My question involves two different problems:
1. A .2500 g sample of a compound known to contain carbon, hydrogen, and oxygen undergoes complete combustion to produce 0.3664 g of CO2 and 0.1500 g of H2O. What is the empirical formula of this compound? The molar mass of the hydrocarbon is 180.16 g/mol, what is the molecular formula?

2. What is the empirical formula of a hydrocarbon which produces 2.703 g CO2 and 1.108 g H2O when combusted?

Ok, so in #2, the question says that the reactant is a hydrocarbon with no specification on whether there is any O in that hydrocarbon. So initially, I thought that all hydrocarbons had only Hydrogen and Carbon atoms. However, in #2, the question states that the hydrocarbon compound contains carbon, hydrogen, AND oxygen. How is it that this hydrocarbon compound has oxygen? And is it the case that if the question only says "hydrocarbon" without specifying any oxygen in the compound, do you assume the empirical/molecular formula only contains C and H?

Thank you.

Chem_Mod
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Re: Hydrocarbons in Combustion

Postby Chem_Mod » Sat Oct 10, 2015 9:16 pm

The first questions is worded poorly (if you wouldn't mind, please let us know where that problem is found so we can make a note). Hydrocarbons only consist of carbon and hydrogen, they shouldn't include any oxygen. So in the second question, you actually are provided all the information you would need to solve the problem.

Erin 2I
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Joined: Fri Sep 25, 2015 3:00 am

Re: Hydrocarbons in Combustion

Postby Erin 2I » Sat Oct 10, 2015 10:47 pm

Thank you. The first question was from the Chem 14A Workbook from Fall 2014, #1 of the Fall 2012 Quiz.

emily c
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Re: Hydrocarbons in Combustion

Postby emily c » Mon Oct 12, 2015 5:30 pm

so does this mean if we are only given the mass of CO2 and H20 and told they are the products, are we to assume that the initial reactants were only CH and O2?

Jacob Afable 3J
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Re: Hydrocarbons in Combustion

Postby Jacob Afable 3J » Tue Oct 13, 2015 10:20 am

For Question 2, this was my work to get the correct solution.
Attachments
image.jpeg

Erin 2I
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Re: Hydrocarbons in Combustion

Postby Erin 2I » Sun Oct 18, 2015 1:12 am

If the question specifies that the reactant is a "hydrocarbon," then the reactant will only contain C and H. If the question does not specify that it is a "hydrocarbon," and you are given the masses of the products CO2 and H2O, then you should start by finding the grams of C and H in the reactant. If the total mass of C and H does not add up to the initial mass of the reactant, then that shows that the leftover mass is from the O. I hope this makes sense..


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