Compound K is a hydrocarbon. Combustion of 6.51 g of K gave 20.47 g of carbon dioxide and 8.36 g of water. The relative molecular mass of K was found to be 84. Calculate the empirical and molecular formula of K

Answer 1

I will outline the solution.
in the 20 grams of CO2, how many grams of C is in that?
In the 8.36 grams of Water, how many grams of H is that?
Now, you started with 6.51 grams of K, you know how much C and H was in it, the rest is O.

Now compute the moles of C,H,O from the masses you found.

Now you have the moles, what is the ratio of CHO? Divide each mole number by the lowest of the CHO moles...you now have the subscripts for CxHyOz

What is the Mol mass of that? if you need to increase the ratios (say 2, or 3) to get the 84 mole mass, do so.