In this example question, it asks what volume in milliliters of 5.2 molar hydrobromic acid must be used to prepare 3.5 liters of 2.7 molar hydrobromic acid. Now, how do we know this is a dilution question? Well, typically in a dilution question, we're only talking about 1 compound. And with that one compound, to be talking about dilution, we tend to deal with 2 molarities. So the fact that we're dealing with just hydrobromic acid and have 2 molarities associated with it is a strong indication that we're dealing with the dilution. That means we're going to use the formula M1V1=M2V2. Now remember, M1 is larger than M2 because it represents the concentrated solution before you've begun dilution. Since 5.2 molar is the larger molarity, it must be M1. Associated with M1 is V1. We don't see any number around it, so V1 is what we're looking for. Now remember also that the word "of", when it's in between two numbers, means multiply. We're going to say here the 2.7 molar is M2, our diluted molarity. We're multiplying it with 3.5 liters, so based on the dilution equation, 3.5 liters must be V2. We will isolate V1. So, divide both sides by 5.2 molar. The molarities cancel out and look, we'll have V1, but it will be in liters. It comes out to be 1.8173 liters. We want the answer in milliliters, so just do a quick metric prefix conversion. Liters are on the bottom, milliliters on top. One milliliter is 10 to the negative 3 liters, so liters cancel out, and that comes out to be 1817.3 milliliters.

Here, 5.2, 3.5, and 2.7 all have 2 significant figures. So if we wanted 2 significant figures here, we would just write this as 1800 milliliters. Oh, it's 1800 milliliters as our final answer. Just remember, when we're dealing with 1 compound and we have different molarities, that's a strong indication that we're dealing with the dilution equation. So use the dilution formula and solve for the missing variable.