Molecular formula of hydrocarbon

[Sam_]

Homework Statement

0.1 dm^3 of a gaseous hydrocarbon may require 0.45 dm^3 of oxygen for a complete combustion to give 300 cm^3 of Carbon dioxide. All volumes are measured in the same environment. Calculate the molecular formula of the hydrocarbon.

The Attempt at a Solution

i tried getting the gdc of 10, 30 and 45 =90. and the have like

9 CxHy + 2 O2 --> 3 CO2 + H2O

but I cannot go further than this. please help. Thanks.

 

[rohanprabhu]

as for the formula you have taken.. i don't understand why you've taken the GCD, but it is fundamentally wrong as the oxygen is not balanced on both sides [and neither is carbon or hydrogen].

What you need is a equation which is prefixed and suffixed by variables on both the sides to get you a linear equation which you can then solve...

 

[chemisttree]

Can you think of a way to calculate the amount of carbon in CO2 and hydrogen in H2O? You have a good start here:

CxHy + O2 --> CO2 + H2O

I've removed the prefixes you had (the '9', '2' and '3'). Can you solve it in terms of 'x' and 'y'?

 

[lana91]

CxHy + (x+y/4)O2 --> xCO2 +y/2H2O

thats the correct answer from ccea spec for alevel chemistry =]