 in this video let us talk about molecular formula and empirical formula. A molecular formula tells us the exact number of atoms in one molecule of any compound. So for example in the case of water H2O, this tells me that there are two atoms of hydrogen and one atom of oxygen in one molecule of water. So this formula is giving me that exact information of the number of atoms. This is a molecular formula. Similarly for benzene the molecular formula will be C6H6. This is telling me how many atoms of carbon and how many atoms of hydrogen exactly are there in one molecule of benzene. For glucose it will be C6H12O6. These are all molecular formulas. They tell me the exact number of atoms. Makes sense. Now empirical formula on the other hand does not tell me information about the exact number of atoms but it tells me the information about the ratio of the number of atoms. For example for glucose the empirical formula will be CH2O. What this is telling me that for every one atom of carbon there are two atoms of hydrogen and one atom of oxygen in a glucose compound. It's not telling me how many exact number of atoms there are in one molecule but it's telling me what is the ratio of the atoms. Similarly if I ask you what will be the empirical formula for benzene can you write it down? Pause this video and give it a shot. For benzene the empirical formula will be simply CH. For every one atom of carbon we have one atom of hydrogen. So the ratio is 1 is to 1. So the empirical formula is CH. What about water? What will be the empirical formula for water? Can you try this? The empirical formula for water is H2O itself. The ratio is 2 is to 1. We cannot simplify it further. So in this case the two are the same but in general the empirical formula only gives us information about the ratio of the number of atoms. Alright what can we do with this empirical formula? Well one thing that we can do with this empirical formula is we can find how much percentage of carbon hydrogen and oxygen will be contained by mass in a sample of glucose. We can calculate that percentage. Let's see how to do that and that is often asked in our problems as well. So we know that this formula is telling me that if I have one mole of carbon then I will have two moles of hydrogen and one mole of oxygen. Because I know that for every atom of carbon I have two atoms of hydrogen and one atom of oxygen. So if I take 6.022 into 10 to the power 23 atoms I am basically taking one mole of carbon I will have two moles of hydrogen and one mole of oxygen. I am just multiplying the number of atoms here. So if I know this I know that for every 12 grams of carbon I will have two grams of hydrogen because two moles of hydrogen is one times two two grams of hydrogen and I will have 16 grams of oxygen because the molar mass of oxygen is 16 and now that I have the masses I can calculate the percentages. So the percentage of carbon will be 12 divided by the total which is 14 plus 16 12 by 30 times 100 percent and the percentage of hydrogen will be 2 by 30 times 100 percent and the percentage of oxygen will be 16 by 30 times 100 percent. So we can calculate the percentages using the empirical formula.