 So let's do some problems involving molar mass. First, what's the molar mass of Sulfur? Well Sulfur is an element so this means we can look it up on the periodic table. So we go to the periodic table and we look for the mass number under the element symbol of Sulfur. So here's Sulfur and there's the mass number, 32.06. Now this means two things, this number. It means that the average atomic weight of a Sulfur atom is 32.06 atomic mass units. And it also means that the mass of one mole of Sulfur atoms is 32.06 grams. From this we directly get the molar mass. If one mole of Sulfur weighs 32.06 grams then the molar mass of Sulfur is 32.06 grams per mole. So either we can write grams per mole as grams slash mole or grams dot moles to the minus one. It means the same thing. Okay how about water? Water is not an element but like everything in the universe it is made up of elements. The formula for water is H2O. So one water molecule is made up of one oxygen atom and two hydrogen atoms. If you have two water molecules then there are two oxygen atoms and four hydrogen atoms. And if you have one mole of water molecules that means you have one mole of oxygen atoms and two moles of hydrogen atoms. This means that we can work out the molar mass of water by adding together the molar masses of the atoms that make it up. So to work this out we need the values for the molar mass of oxygen and the molar mass of hydrogen. So we go back to the periodic table and we find oxygen here at 15.999 and hydrogen here at 1.008. So we're going to go back and put those in and then we're going to calculate that. And it comes out as 18.015 grams per mole. Don't forget the units. So that means that one mole of water weighs 18 grams.