In this example problem, we will determine the molecular formula of a hydrocarbon using combustion analysis. The problem reads: upon combustion, a hydrocarbon produces 25.15 grams of CO2 and 11.58 grams of H2O. The molar mass of the hydrocarbon is 114 grams per mole. Find the empirical and molecular formulas of the hydrocarbon. Our first step is to convert to moles of each element in the compound. In combustion analysis, we're making an assumption that all of the moles of carbon in the hydrocarbon will produce CO2 and all of the moles of hydrogen in the hydrocarbon will produce H2O. So, we'll want to convert 25.15 grams of CO2 into moles of carbon and 11.58 grams of H2O into moles of hydrogen. To convert grams of carbon dioxide into moles of carbon dioxide, we need the molar mass. The molar mass of carbon dioxide is 11.011 + 2 * 16, which is 44.011 grams per mole. We can use this as a conversion factor to convert from grams of carbon dioxide to moles of carbon dioxide. Then, we can use the chemical formula for carbon dioxide to convert from moles of carbon dioxide to moles of carbon. If we put this into a calculator, we should get 0.5714 moles of carbon. Now, we can convert grams of H2O into moles of hydrogen. First, we'll need the molar mass of H2O. There are two hydrogen atoms and one oxygen atom, so that's 18.106 grams per mole. We'll use this to convert from grams of H2O to moles of H2O. Then, we can use the formula for H2O to convert from moles of H2O to moles of hydrogen. And there are two moles of hydrogen for every 1 mole of H2O. If we put this into a calculator, we should get 1.286 moles of hydrogen. The next step is to find the smallest whole number ratio of atoms for carbon and hydrogen. To do this, first, we'll want to divide by the smallest number of moles. The smaller number of moles is the moles of carbon, so we'll divide both the moles of carbon and the moles of hydrogen by 0.5714. This will give us numbers that are 1 or greater for the moles of all of our elements. Now, we need to eliminate decimals by multiplying by a multiplication factor. We want to eliminate the decimal point to five from hydrogen, so we can multiply all of our numbers by four. Now, carbon is four moles and hydrogen is nine moles. So, our empirical formula is C4H9. Using the empirical formula and the molar mass of the hydrocarbon, we can determine the molecular formula for the hydrocarbon. First, we'll want to calculate the molar mass of the empirical formula. There are four carbons and nine hydrogens, so that's 57.116 grams per mole. Now, to determine the multiplication factor to convert our empirical formula into the molecular formula, we'll take the molar mass of the molecular formula divided by the molar mass of the empirical formula. In the problem, we're told that the molar mass of the molecular formula is 114, and we've calculated the molar mass of the empirical formula to be 57.116. So, our multiplication factor is two. Therefore, our molecular formula is twice our empirical formula, which is C8H18.