Question

An unknown compound contains only C, H, and O. Combustion of 5.40 g of this compound produced 10.8 g of CO2 and 4.42 g of H2O.
What is the empirical formula of the unknown compound? WILL GIVE MEDAL

Answer 1

Well first off, you have a combustion reaction, so you might want to write it down. It might make things a bit easier to follow. Combustion is given by: \(C_a H_b O_c + O_2 \rightarrow CO_2 + H_2O\) and what you're trying to solve for is the a, b, and c values that you have there. [NOTE: it's important that you know combustion reaction very well].
Now, notice you have the mass of the products. Well, find the mass of carbon dioxide (do the same thing for water) and find the moles! and then use dimensional analysis to cancel terms to get units of moles only.

Since ur only worried about the equation, you only really care about the relationship between moles of CO2 and H2O. You might get a value raised to the -4 of -3, or whatever value. Just ignore that for now and use the decimal values. Now, you will probably (most likely) get some sort of decimal value, but that's not good. That's actually rally ugly. So, simplify the decimals into actual whole numbers. you'll probably get some large number. Well, to make it easier, simplify it. Find the GCF to get simpler values, such as values between 1-10 (if possible). With this information, it's nothing but balancing a chemical equation :)

Look at the values for CO2 and H2O. You should be able to deduce an empirical formula from what you have so far! If this is all you need, you can stop here, but note that you ARE still missing the value for oxygen which involves a few more steps. I'll leave it here for now.