if we can determine the percent composition of a compound it is easy to determine the empirical formula once again this is the lowest whole number ratio of the number of atoms of each element within a compound this will really only involve one additional step than the situation where we have the masses of each element because we can take the percentages and convert them into some convenient hypothetical Mass for example let's say we know that the percent composition of a compound containing carbon and oxygen is 27.29 percent carbon and 72.71 percent oxygen all we need to do is simply assume that we have a hundred grams of the substance it doesn't matter what this number is because any amount of it will display the same percent composition and if we choose a hundred grams it makes the math nice and easy if we have a total of a hundred grams that means we will have 27.29 grams of carbon and 72.71 grams of oxygen now we just continue with the strategy we already know use the molar mass of each element to convert into moles for that element 27.29 grams of carbon times 1 mole over 12.01 grams gives us 2.272 moles of carbon atoms 72.71 grams of oxygen times 1 mole over 16 grams gives us 4.544 moles of oxygen atoms dividing both numbers by the smaller number will hopefully give us this ratio in terms of integers 2.272 over 2.272 gives us 1 for carbon and 4.544 over 2.272 gives us 2 for oxygen this means that carbon atoms and oxygen atoms are present in a one to two ratio in this compound resulting in an empirical formula of CO2 this could represent carbon dioxide or a larger compound with the same numerical ratio let's try one more if a compound is 40 carbon 6.71 percent hydrogen and 53.28 oxygen by Mass what is its empirical formula once again assuming 100 grams we get the masses of each element from the masses of each element we can convert to moles and finally get these in an integer ratio we should get ch2o as the empirical formula for this compound