[brycebb]

A mixture of butene and butane is burned in air to give carbon dioxdide and water.  Suppose you burn 2.86g of the mixture to obtain 8.80g of carbon dioxide and 4.14g of water.  What are the mass % of butene and butane in the mixture? 

Now normally in my textbook this kind of problem only asks for you to find the empirical formula of the unknown hydrocarbon from the products produced.  However in this one its a mixture when you already know the hydrocarbons.  Now I approached this problem like I did the other problems, I took 8.80g of carbon dioxide and converted it to .199 mol C and took 4.14 g of water and converted it to .459mol of H.  Now normally you would divide by the smaller value to get the carbon to hydrogen mol ratio and find the empirical formula for the hydrocarbon, but since I don't have to I got a bit lost.  I know you have to use the masses of carbon dioxide and water to find the masses of butene and butane, but I am sad to say I am stuck and can't figure out how.  I know this is probably a simple problem, but I've spent quite some time on it and it has become very irritating.  Here is the work I have done so far


8.80g CO2(1mol/44.0098g)(1molC/1molCO2)= 0.199molC
4.14g H2O(1mol/18.0152g)(2molH/1molH2O)=0.459molH

I do not know to go from here, I have tried multiple methods and cannot come up with the correct answer. 

[Hunter2]

I would approach how you start. Calculate the ratio of C and H. Butane and butene has 4 C each. Try to get the right number by starting with 8.

[brycebb]

I would approach how you start. Calculate the ratio of C and H. Butane and butene has 4 C each. Try to get the right number by starting with 8.

find the ratio of hydrogen to carbon and multiply that by 8? is that what you are referring to?

[AWK]

Generally you should set a system of two equation
m1 + m2 = 2.86
and mass of C in m1 grams of C4H8 + mass of C in m2 grams of C4H10 = mass of C in CO2
or mass of H in m1 grams of C4H8 + mass of H in m2 grams of C4H10 = mass of H in H2O
Note - you have an excessive information - mass of CO2 or mass of H2O only is sufficient to solve this problem.

[brycebb]

Generally you should set a system of two equation
m1 + m2 = 2.86
and mass of C in m1 grams of C4H8 + mass of C in m2 grams of C4H10 = mass of C in CO2
or mass of H in m1 grams of C4H8 + mass of H in m2 grams of C4H10 = mass of H in H2O
Note - you have an excessive information - mass of CO2 or mass of H2O only is sufficient to solve this problem.

wow, thanks a lot, I feel stupid now for asking.  but thank you for the input.