 Okay, so we know that one of the powerful things about a chemical equation is that it allows us to make predictions about amounts of chemicals. For instance, in this hypothetical reaction we know that if we have two moles of A we will need one mole of B to react completely with it and that when that has happened we'll have three moles of C, the product. But no one has a setup in their lab that automatically measures moles. Design project for you, come up with one that does. What we do have generally are setups to measure mass and volume. So in order to make predictions that are really useful and measurable we need to convert our mole predictions into mass or volume predictions. Happily we already have a strategy for doing this. You know that it's possible to convert moles of a substance into mass or number of particles or volume if it's a gas. The conversion factors are either a proper constant like Avogadro's constant or a constant under defined conditions such as the gas-molar volume or can be calculated from information on the periodic table like the molar mass. So what we need to do is combine this skill with our understanding of mole ratios so that we can move freely between quantities of various reactants and products regardless of what unit we're measuring in. So let me take this conversion map and rearrange it slightly. I'm putting it all over on the left here and I'm going to specify that I'm talking about one particular chemical. Let's just label it A. Then I can reflect the map over to the other side of the page for another chemical B. So on the left hand side of the page I have the conversions that will let me move between mass, particles, volume and moles of A and on the right I have the same thing for B. And how do we relate A and B to each other? Well if they're both involved in a chemical reaction and we can write the equation for that reaction then we know the mole ratio in which they react, the stoichiometric ratio. So what we've done now is summarise what we know so far into a map and I'm going to honour Aaron Sams and Jonathan Bergman here who are the chemistry teachers in the US who came up with the idea of flipped learning in the first place and I'm going to borrow their name for the map which is called the land of the mole. So what this diagram does is map out the calculation path that you would take for any given stoichiometric problem. For instance, if you had a certain mass of reactant and you wanted to know what mass of product it would give you would convert the mass of the reactant to moles, you'd use the mole ratio to calculate the moles of product that would be produced and then you'd convert the moles of product into a mass. Quick tip for you, the most common conversions that you're going to need are the mass mole conversions. You do need to know how to do the particle and volume conversions but in terms of calculations that you're most likely to need as you work in the lab, the mass to mass calculations will be far and away the most useful.