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Question

A. The hydrocarbon burns completely, producing 7.2 grams of water and 7.2 liters of CO2 at standard conditions. What is the empirical formula of the hydrocarbon?

B. Calculate the mass in grams of O2 required for the complete combustion of the sample of the hydrocarbon described in A.

C. The hydrocarbon dissolves readily in CHCl3. The freezing point of a solution prepared by mixing 100 grams of CHCl3 and .6 grams of the hydrocarbon is -64 degrees celsius. The molal freezing point depression constant of CHCl3 is 4.68 degrees celsius/molal and its normal freezing point is -63.5 degrees celsius. Calculate the molecular weight of the hydrocarbon.

D. What is the molecular formula of the hydrocarbon?

Answer 1

A. See how many MOLES water and carbon dioxide you have. This tells you ratio of H to C (remember; two H in each H2O). This gives you empirical formula.

B. Just the mass of oxygen in the CO2 and H2O in A. Again, go via moles.

C. Use definition of molar depression of freezing point to find number of moles of hydrocarbon, and hence its molar mass.

D. It must be equal to the empirical formula,or some multiple of it,consistent with (C).