2
$\begingroup$

How many moles of carbon dioxide are there in $20.5~\mathrm{g}$ of oxygen gas given this reaction: $\ce{C15H30 + O2 -> CO2 + H2O}$

So I figured out the balanced equation is $\ce{2C15H30 + 45O2 -> 30CO2 + 30H2O}$ I thought that the ratio between moles of oxygen gas and that of carbon dioxide would be $45/30$. And then I know that the moles in $20.5~\mathrm{g}$ of oxygen gas is $0.640~\mathrm{mol}$. The answer I got from cross multiplying is different from the answer key, which is $19.2\ \mathrm{mol}$.

I dont see any problem with my method. So I am wondering if there is anything wrong with the answer key or I misunderstood the question.

$\endgroup$
  • 1
    $\begingroup$ Hi and welcome to chemistry.stackexchange.com. Feel free to take a tour of the site. I improved the formatting of your post with MathJax; for more information on how to do so yourself, consult the help center or visit this or this meta-post. Your question is a homework question, therefore I am pointing you to our homework policy. By the way, what is the actual question? ‘How many moles of $\ce{CO2}$ are there in $\ce{O2}$ gas?’ $\endgroup$ – Jan Nov 15 '15 at 17:51
1
$\begingroup$

How many moles of carbon dioxide are there in $20.5~\mathrm{g}$ of oxygen gas given this reaction: $\ce{C15H30 + O2 -> CO2 + H2O}$

Assuming that there is enough hydrocarbon for complete consumption of the $\ce{O2}$, then oxygen is used in ratio of $2:1$ for the products $\ce{CO2}$ and $\ce{H2O}$. Since you started out with 20.5 g (20.5/32 = 0.641 mol) of $\ce{O2}$, then (2/3)*0.641 = 0.427 mol $\ce{CO2}$.

I notice that if you start out with 20.9 grams of $\ce{O2}$, then you get 19.2 g $\ce{CO2}$. So something is wrong with the whole problem as you have given it.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.