 Okay, today we're going to talk a little bit more about molarity and we're going to do some practice problems working with molarity. So you'll remember molarity is a measure of concentration represented by capital M. It's equivalent to moles of solute per liter of solvent. And so that means a one molar solution is one mole per one liter. For the purposes of this course, the solvent is likely to be water. And for the purposes of when you're working in the lab after you've completed this course, you may also find that your solvents are often water. Sometimes they're alcohols or some other solvents. But if you have a water-based solution, it's known as an aqueous solution, which is sometimes designated by an AQ in parentheses. So if you see that, you'll know that you're dealing with water as a solvent. Same with aqueous. So for example, when you're asked how would you prepare one liter of a one molar aqueous solution of potassium nitrate, you know that you're dealing with dissolving in water. So in order to tackle a problem like this, we're going to start out the same way we did with calculating the molecular weight of a molecule because we need to know how much the potassium nitrate weighs for one mole. So we have one potassium, one nitrogen, and three oxygen atoms. We're going to use our periodic table, see that potassium is 40.078, see that nitrogen is 14.007, and oxygen is 15.999. Okay, again, we're going to multiply by the number of atoms in the molecule. So these two are just one, and oxygen is three, 15.999 times three is 47.997. And then we're going to add all three of those together. And that's going to give us a total molecular weight of 102.082 grams per mole of potassium nitrate. And so we need to determine how we would prepare one liter of a one molar potassium nitrate solution. So we have 102.082 grams per mole. And we need a one molar solution, which means we need one mole per liter. So those moles will cancel. And we'll know we need 102.082 grams per liter. So then you need to dissolve 102.082 grams of potassium nitrate in water and bring to the volume of one liter. So that's how we would prepare a one liter of a one molar potassium nitrate solution.