 So this lesson is going to be on mass concentration and molar concentration. So as we talk about in the lesson on solutions and number of concentration, concentration is defined as the amount of constituent per an amount of volume, and number of concentration is defined as the number of entities per an amount of volume, but that's only applicable for a system with a very small number of constituents. In practice in chemistry, that is usually not the case because you usually will be dealing with a very large number of entities, so you will be more often using mass and molar concentrations. So mass concentration is defined as the mass of a constituent mi, divided by the volume of the mixture, v, and molar concentration is defined. It's similar to the number of concentration, but the amount of constituent is represented in moles instead of number because there are just too many of them. So let's do a question. Say you put 2.1 grams of sucrose in a cup and filled a cup with water onto the 1.5 liter mark. Let's calculate the mass concentration and the molar concentration of this solution. So the mass concentration of sucrose in this solution is equal to the mass of constituent, which is 2.1 grams, divided by the amount of volume, which is 1.5 liters, which is equal to 1.4 grams per liter. So this is the mass concentration of sucrose. It tells you that for every liter of this solution, you get 1.4 grams of sucrose. Now let's calculate the molar concentration of sucrose. So the molar concentration of sucrose in this solution is equal to the number of moles of constituents, divided by the corresponding amount of volume. We know that the volume is 1.5 liters, so we don't know the number of moles of sucrose. So we do need to calculate that first. All right. So how do we do that? First, you would need the molar mass of sucrose, which is 342.3 grams per moles. Now the number of moles of sugar in 2.1 grams of sucrose is 6.1 times 10 to the minus 3 mole. So we got our number of moles of sucrose. Now we have all the ingredients that we need to calculate the molar concentration of the sucrose solution that we made. C equal n divided by V, so that's equal to 4.1 times 10 to the negative 3. And the unit, as you can see from the calculation, it is more divided by liters, so the unit is more per liter. There's also another unit for this, which is practically mean the same thing, and it's molar. So I would say that this is equal to 4.1 times 10 to the negative 3 molar. The symbol is Big M, so you will quite often see people use this unit to represent the molar concentration, but you should know that it translates to more per liter.