Finding the Empirical formula.... ?

Question

What is the empirical formula of a hydrocarbon if complete combustion or 4.500 mg of the hydrocarbon produced 15.212 mg of CO2 and 3.113 mg of H2O? Be sure to write C first in the formula.

Also.. What is the molecular formula if the molar mass of the hydrocarbon is found to be about 50

Do I convert to grams first?

Answer 1

sure, but just call them grams, it would still be the same ratio.

find moles, using molar masses:

? moles carbon in 15.212 g CO2 @ 1 mol C / 44.0 g CO2 = 0.346 mol C

? mol Hydrogen in 3.113 g H2O @ 2 mol H / 18.0 g H2O = 0.346 mol H

ratio of moles is 1:1

your answer is: C1H1 is the empirical formula

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the empirical formula has a mass of 13

the molar mass @ 50 is about 4 times more massive, (4 x 13  = 52)

your answer: C4H4 is the molecular formula