Elemental analysis of a carbohydrate X showed the sample contained 48.7 % carbon and 8.1 % hydrogen by mass. Find the empirical formula of X.

These sorts of questions can look difficult, but if you learn the steps needed to solve them then they are all very similar.Step 1: Since we are told that X is a carbohydrate, we know that the only other constituent element must be oxygen. Step 2: Then we need to convert our percentage mass into moles. We aren't given absolute masses in this puzzle, so we can assume that the total mass is 100 g to simplify the numbers. Step 3: To convert our masses to moles we divide by the relative atomic mass of each element in turn. Step 4: Divide the moles of each element by the lowest number of moles present. In this case it is oxygen. Step 5: An empirical formula is the simplest whole number ratio of atoms of each element in a compound. In this example we can find it by doubling the numbers of moles of every element. Step 6: In step 5 you worked out the number of moles of each element in the empirical formula, but the examiner asked you to give the empirical formula so don't forget to write it clearly at the bottom of the page.