In this example problem, we'll calculate the molecular formula for an organic compound from experimental data. Our problem states that a certain organic compound is found to contain 56.25 percent carbon, 6.29 percent hydrogen, and 37.46 percent oxygen. Its molar mass is 256.26 grams per mole. Find its molecular formula. The first thing we want to do to solve this problem is to determine the empirical formula of our compound. The empirical formula is the smallest whole number ratio of atoms of each element in the compound. The first step to calculating the empirical formula is to find the moles of each element in a certain sample of the compound. Because of the law of definite proportions, we can use any size sample of the compound that we want, and we should get the same answer for the smallest whole number ratio of atoms of each element. I'm going to choose to use 100 grams of the compound as my sample so that it's easy to convert from percent of each element into grams of each element. So, given a 100 gram sample of the compound, there will be 56.25 grams of carbon, 6.29 grams of hydrogen, and 37.46 grams of oxygen. Now I'm going to convert these numbers into moles. There are 12.011 grams of carbon for every one mole of carbon, which gives us 4.683 moles of carbon. There are 1.008 grams of hydrogen for every mole of hydrogen, which gives us 6.240 moles of hydrogen. And there are 16 grams of oxygen for every mole of oxygen, which gives us 2.341 moles of oxygen. Now that I have my units of moles of each element, I can find the smallest whole number ratio of atoms in the compound. To find my smallest whole number ratio of atoms, my first step will be to divide all of the numbers by the smallest number of moles. Oxygen has the smallest number of moles at 2.341, so I'll divide all three of the moles by 2.341. I want to get whole numbers, and right now, moles of hydrogen is 2.666. I want to get rid of the decimal point 666. I know that 0.666 is two-thirds, so I can multiply all three of these numbers by three to eliminate the decimal. When I multiply all these numbers by 3, I'll have 6 moles of carbon, 8 moles of hydrogen, and 3 moles of oxygen. So, my empirical formula is C6H8O3. Now, I can use the empirical formula and the molar mass given in the problem to find the molecular formula. First, I'll calculate the molar mass of the empirical formula. There are 6 carbon atoms, 8 hydrogen atoms, and 3 oxygen atoms in the empirical formula, so the molar mass is 128.13 grams per mole. I need to find the multiplication factor to convert my empirical formula into my molecular formula. To find that multiplication factor, I divided the molar mass of the molecular formula by the molar mass of the empirical formula. The molar mass of the molecular formula given in the problem is 256.26 grams per mole, and the molar mass of the empirical formula that I've calculated is 128.13 grams per mole. So, my multiplication factor is 2. To find my molecular formula, I take the empirical formula x 2, and I get C12H16O6.