 Now, I want to talk about the concept of pH. pH is a measure, well, when you think of pH, you probably think of acids and bases, right? Of course you do. So we're going to look, now pH is an extremely important characteristic or quality or descriptor in a system because it tells you essentially the concentration of hydrogen ions in a system. Now, the more hydrogen ions you have, the more acidic your substance is. So acids have a lot of hydrogen ions and bases don't have as many hydrogen ions and this is all relative. Do you remember that picture that I drew you? I drew you in a picture. I drew you a chemical reaction, hydrogen ions and hydroxide ions and we can go back and forth and we make water. What this reaction right here is actually happening all the time in all watery systems. We're bouncing around from hydrogen ions and hydroxides to water back to hydrogens and hydroxides. You have a bunch of these guys in the system. You're going to have an acidic system. If you don't have very many, you're going to have a basic system. Now, who cares? Like why? Nobody cares. This is wild and this is the magic of chemistry. For some reason, the hydrogen ion, and this is why it's relevant in living systems. For some reason, the hydrogen ion messes with protein structure. We're going to look at protein structure. We're going to build proteins. DNA, found in the nucleus of all your cells, is used to build proteins and proteins are the machines in your body that do all the work. Here I go. Look at me go. I'm doing all proteins, doing work to make me do all these crazy things. Crazy. If you have a substance that messes with that, you are going to end up with funkiness, like wackadoosicalness, and you're going to get sick. Sorry, I don't want you to get sick. Your blood has a super narrow pH range that you need to stick in. You have to have the exactly proper amount of concentration of hydrogen ions. Okay, so what is that amount? Well, here's the thing. Atoms are hard to count. Do you have a sense of that? That an atom, like, okay, is it one hydrogen ion makes something acidic? Is it 10 hydrogen ions that make something acidic? No, it's a mole, or a part of a mole. Okay, so stick with me here. Let me talk about atom quantities in moles. So one mole of anything is equal to 6.02 times 10 to the 23rd anythings, just like one dozen is equal to 12 anythings. I would love to have a dozen donuts, and you know, oh, man, that makes me, like, drool just thinking about it. I would love to have a dozen donuts right now, and you would know, dude, she's got 12 donuts right there, and let's take some bets on how fast she's going to eat them, and I'm going to say do that in about 10 seconds, and they're all going to be gone, because that's how good a dozen donuts sound to me. I could have a mole of donuts. How many donuts would I have? 602 sextillion. I should write that out for you, because I can't help it. 602, that's 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 zeros. What? No, that's so crazy. Big number. If I had a mole of donuts, they would like, oh my gosh, wouldn't that be a fun, fast fact? How many buildings would I need to hold a mole of donuts? I think they would cover, like, the whole planet, and they probably would, like, engulf the whole planet and go, like, miles into the air if I really did. Oh my gosh, that would be a fantastic math problem. Somebody knock yourself out and then report back. How big would my pile of donuts be if I had a mole of donuts? A mole, one mole of hydrogen ions is one gram, which is basically a paperclip. That alone should tell you, like, dude, atoms are so small. Okay, why do we care? Well, we care because we have to talk about, if we're going to talk about pH, we have to talk about concentration of hydrogen atoms, hydrogen ions, and concentration is the number of particles of something in a volume of a solution. So particles, particles of, we call it a solute, and the hydrogen ions are the solute. And what do you think the solvent is? What a... So if we want to know the pH of something, we have to know how many hydrogen ions there are in a volume of solution, and I will tell you right now that we measure that in molarity. So the molarity of a solution, for example, a one molar solution is one mole of particles in one liter of solution. So a molar solution of, say, hydrochloric acid has a mole, 602 sextillion hydrochloric acid particles in a liter of water. A two molar solution is going to have two moles of particles. Now, we could say, let's measure something in a dozen molarity, and just that would be how many dozen particles are in a liter of solution. And if we were measuring the doughnut pool, I'm not even going to try and carry my analogy on. I should stop thinking about doughnuts because I have more lectures to do tonight before I'm finished. And then I'm stopping at the doughnut store, guaranteed. Okay, molarity, yeah, yeah, yeah, because molarity is how we're going to measure our hydrogen ion concentration. I want to talk about the pH. I want to talk about the pH of what is pH and what is the pH scale. So I'm going to carry this over to the next little lecture where now you're going to have to use the molarity of a solution in terms of the molarity of hydrogen ions. And then we're going to see what is pH in the first place or the second place or the third place.