Styrene, the building block of polystyrene, is a hydrocarbon, a compound consisting only of C and H. If 0.438 g of styrene is burned in oxygen and produces 1.481 g of CO2 and 0.303 g of H2O, what is the empirical formula of styrene?

Question

abb0t · Answer

Start by writing down the equation for combstion and styrene.

abb0t · Answer

C$_8$H$_8$ + O$_2$ $\rightarrow$ CO$_2$ + H$_2$O

abb0t · Answer

Next, find your moles of water and carbon dioxide.

abb0t · Answer

I'll just wait for you to come back. I dont want to explain something if you may not come back.

anonymous · Answer

Okay :)

anonymous · Answer

Hold on

anonymous · Answer

Now what? o:

abb0t · Answer

Well, did you find the moles of water and carbon dioxide?

anonymous · Answer

I got 0.034  mol CO2 & 0.017 mol H20

abb0t · Answer

Ok, now divide by the higher of the two values, you should get a integer value.

abb0t · Answer

intuitively,  you should see that your ratio is 1:2

anonymous · Answer

by 0.017?

anonymous · Answer

Ohhhh

abb0t · Answer

yes. so you know that your ratio of water and carbon dioxide is 1:2, correct. Are you with me so far.

anonymous · Answer

Yes (:

abb0t · Answer

Therefore, you'll notice that you have a 2:2 ratio of hydrogen AND carbon. Remember your formula from above.

anonymous · Answer

So would I be left with C2O4 & H2O?

abb0t · Answer

2CO$_2$ + H$_2$O 

notice you have 2:2 which is the same thing as 1:1 ratio. Therefore, your formla for styrene must be 1:1
But, let's check that.

abb0t · Answer

2 for Carbon and 2 for hydrogen. YES.

anonymous · Answer

Ok :) I'm following

abb0t · Answer

Now, what you do is repeat the same process above with CH and O$_2$ (on the left side).

abb0t · Answer

because NOW you know that you have Carbon AND hydrogen.

abb0t · Answer

So, find the moles of CH and O$_2$. Can you do that?

abb0t · Answer

btw, if at any point in time, you're confused as to what I'm doing, please ask.

anonymous · Answer

You mean by balancing?

abb0t · Answer

Well, you can do it by balancing, but just to be sure of your answer, you want to do what you did on the other side (on the right). Finding moles by calculation.

abb0t · Answer

However, you don't know the mass, so just give it a variable, say $x$.
(12.01 + 1.008)$x$ = approximate molecular mass of styrene.

anonymous · Answer

Oh okay, I understand now :) The ratio is C  to H is 1 so its CH

abb0t · Answer

Yes.

abb0t · Answer

that is the $empirical$ formula, not molecular formula. Do not confuse them.

anonymous · Answer

Yeah, thank you so much :)