1. Concentration (not the “thinking very hard” kind of concentration)

2. Concentration Matters Sometimes, how much stuff you have is less important than how concentrated it is. Consider two bottles of Kool Aid, each with 1 scoop of powder added: vs

3. Concentration Matters Sometimes, how much stuff you have is less important than how concentrated it is. Consider two bottles of Kool Aid, each with 1 scoop of powder added: vs I’m going to drink the good one 

4. Concentration Units All units of concentration are a ratio (what else?): amount of stuff dissolved vs how much it’s dissolved in (solute)(solvent) The mixture of the two is a solution There are many units out there, but most of them are bad:

5. Concentration Units All units of concentration are a ratio (what else?): amount of stuff dissolved vs how much it’s dissolved in (solute)(solvent) There are many units out there, but most of them are bad: Percent: The vinegar was listed as 5% acid. The problem is, 5% by what? The unit is unclear 5% by weight ≠ 5% by volume ≠ 5% by moles

6. Concentration Units All units of concentration are a ratio (what else?): amount of stuff dissolved vs how much it’s dissolved in (solute)(solvent) There are many units out there, but most of them are bad: Percent: The vinegar was listed as 5% acid. The problem is, 5% by what? The unit is unclear 5% by weight ≠ 5% by volume ≠ 5% by moles Mass per volume: usually given in grams per 100 mL. This is better, because at least you know the units, but there’s still a problem: 5 g/100 mL NaCl (aq) is more concentrated than 5 g/100 mL CaCl 2 (aq) Calcium chloride is heavy, so five grams is actually less stuff (fewer formula units)

7. Molarity

9. An Annoying Detail Let’s say I’m making that 3M salt solution. I go and get myself 6 moles of salt, and 2 liters of water: +

10. An Annoying Detail When I mix them, it won’t be 2L anymore—the salt takes up space.

11. Proper Procedure Put your 6 moles of salt in, then fill it up until the total gets to 2L.

12. Why Molarity?

13. Summary