empirical formula of the question in description

Question

A 2.21g sample of a compound consisting of carbon, hydrogen, oxygen, nitrogen, and sulfur was combusted in excess oxygen. This produced 2.39g CO2 and 1.3g H2O. A second sample of this compound with a mass of 5.64g produced 3.7g SO3. A third sample of this compound with a mass of 8.41g produced 4.34g HNO3. Determine the empirical formula of the compound. Enter the correct subscripts on the given chemical formula.

Answer 1

To solve this problem, you first need to determine the percent composition of each element in the original sample. You know that all of the carbon in the sample will become CO₂, all of the hydrogen in the sample will become H₂O, etcetera. Therefore, we need to set up some mole conversions. Start with 2.39 g CO₂, convert it into moles of CO₂ (by dividing by its molar mass of 44.01 g/mol), then convert it into moles of C (there is 1 mole of C in every 1 mole of CO₂), and then convert that into grams of C (by multiplying by its molar mass of 12.01 g/mol). You should find that the 2.21 g sample contains 0.652 g of carbon (C) in it. This is 29.5% of the original sample. Repeat this process with the 1.3 g of H₂O to determine the mass of H (remember that there are 2 moles of H in every 1 mole of H₂O) and then find the percent of H in the original sample. Continue this process with S (from the 5.64 g sample of SO₃) and N (from the 8.41 g sample of HNO₃). Finally, you should have calculated the percent compositions of C, H, N, and S. You know that all of the percentages must add up to 100%, so you can subtract these values from 100 to determine the percent composition of oxygen.

Once you have determined the percent compositions of all five elements in the sample, it becomes a simple empirical formula problem. Assume a 100g sample, so all of your percentages become grams. Use each element's molar mass to convert the grams into moles and then divide them all by the smallest number of moles to determine the empirical ratio.