 Okay, we're going to build the pH scale. And this is actually an interactive thing. So I'm going to be asking you questions and giving you jobs. And if you need to pause me, by all means, pause away any other time you're not allowed to pause me. But this time you are. So let's go ahead and take a look at this activity. The first thing, let's see if I'm all, is this going to work? The first thing that we're going to do is draw a scale. So you, you could drive your scale any way you want. You can draw it up and down, you can draw it in like a diagonal from left to right from right to left. It doesn't matter. But we're going to add labels to our scale. You can do it the same as I do it, which is going to let you follow along with me. But the way I'm doing it is just one way to do it. So the way I'm going to label this image or this, this, whatever that thing is, the scale down the bottom is I'm going to label the left side acidic. And then I'm going to label the right side basic. This is easy so far, huh? What do you think I'm going to label the middle? Maybe you should put neutral in the middle. You now have labels on your scale. Take a look at that thing. That's exactly the way I labeled it in the lecture previously. So we're looking at it the same way and in all actuality, most scales label it in this order. So that makes it easier for our brains. Next, we're going to add relative hydrogen ion concentration. So now what I want you to add in here is where do you expect a high hydrogen ion concentration and where do you expect a low hydrogen ion concentration? And I gave you the little symbols to add. Now you're going to add it somewhere. I think I have a box for each of them to go into. So take a minute and figure out which end of the scale, the acidic end or the basic end gets this low hydrogen ion concentration symbol box right here. And which one gets the high hydrogen ion concentration? And let's see. Let's just do the low first. You have a guess for where you're going to put the low hydrogen ion concentration. Okay, let's see if you agree with me, except in order for this to work. Don't worry, I can't see over my notebook thing holder. My holder of my notebook is like over my keyboard, so I can't see. That's what we're moving first. And is that where you put the low hydrogen ion concentration? I hope so, because that's where it goes. It goes on the basic side, which means where does the high hydrogen ion concentration go? It goes into the acidic side. Okay, so far this is an easy game, isn't it? Well step three, I want you to add some actual hydrogen ion concentrations and watch what we're going to do. I'm going to give you three actual concentrations. And I want you to look at what these actually are. So this first one is, we'll deal with the first one first. And this is actually one-tenth, one-tenth molar solution. So this, we're looking at molarity. We have a one-tenth to the negative one, which is a one-tenth molar solution. We have a one-tenth to the negative seven, and we have a one-tenth to the negative 14. So if you look at this first one, it's actually a point one molar solution. We're good with that? If you look at the second one, what is that actually? If you had to look at that number, how would you write that number out? I'm going to go ahead and do it for you. If negative one made a point, like it moved the decimal point. We had a one, and we moved the decimal point one place. Then a negative seven, a tenth of the negative seven, we're going to move the decimal point from the one back seven places so that you end up with this. That's actually one-tenth millionth of a mole. That's a smaller number, wouldn't you say? And how about this one? What do you think this one is? It's 14. We're going to move the decimal point 14 places, and we're going to end up with all those zeros in front of the one, and that's one-hundred trillionth of a mole. So look at what these things mean now. We have three different concentrations. We have a tenth of a mole, something else of a mole, and a hundred trillionth of a mole of hydrogen ions in a liter of water. Are you getting a sense of where the biggest concentrations are? I hope so. Okay, so now I want you to add the actual hydrogen ion concentrations, those molar numbers to your chart. I'm going to tell you that one is going to fit on each one of these lines that we've got created here. So let's go ahead and start here with this first arrow. Which one of these concentrations do you think is going to fit in a place where we want a higher concentration of hydrogen ions? Did you take a wild guess? Okay, I'm going to move this one. Did you take the first one because it has more hydrogen ions? One times ten to the negative one, there's a tenth molar solution, and that's more hydrogen ions than any of the other ones, which is why it goes on the acidic side. Where do you think? I think I'm doing the basic one next. Which one do you think is the most basic? Which one of those that's left has the fewest number of hydrogen ions in it? Did you pick one times ten to the negative fourteen? I hope you did because that is indeed the most basic solution that has the fewest hydrogen ions in that concentration. And what does that mean about one times ten to the seven? Where would you put it? Okay, this is awesome. I give you three options. You can either put it right in the middle at neutral, or you can put it between neutral and acidic, or between neutral and basic. Where do you think that seven is actually going to end up fitting? I mean the one times ten to the negative seven. That was a gigantic hint for you all. It does indeed go at the seven. Now what do you notice? Neutral is in the middle. We definitely, our numbers actually do tell us some information about the number of hydrogen ions, and we have a fourth step. Now we're going to add actual pH values to our scale. Are you getting an idea of where those pH values are actually going to come from? Well here are a pile of pH values, and I think I want us to start, let's go ahead and start with number fourteen, because why would you start with zero or one? If you had to take a wild guess, where is something that sort of might make you think fourteen could go? How about in the zone where the concentration of hydrogen ions is one times ten to the negative fourteen? Where would you put the seven? Where you have one times ten to the negative seven? Hydrogen ions in a liter of solution, moles of hydrogen ions in a liter of solution. Where are you going to put the one? Where you have one times ten to the negative one? Moles of hydrogen ions in a liter of solution. Where are you going to put four? Now we don't have a number to match. Now we have to estimate, are we going to put this on the acidic side of things or are we going to put it on the basic side of things? It's definitely going to be on the acidic side. How about your nine on the basic side and what about the zero? Yeah, totally on the acidic side. One times ten to the zero power is one and that means there's one mole of hydrogen ions in one liter of solution and the pH is zero. Okay, what started as like, dude, how is this even possible? This doesn't make any sense. It's counterintuitive. Now goes, oh, it's because and my kid was just in here, I think today telling me that he just learned that the pH scale is logarithmic. This is a logarithmic scale. Each number is actually increasing by powers of ten instead of just by powers of one. So the concentrations are vastly different on this scale, but also the numbers are related to the exponents and not the one doesn't mean only one hydrogen ion and the fourteen means well there's fourteen hydrogen ions, it's actually to the power of negative one and to the power of negative fourteen and you can see why to the power of negative fourteen is a much smaller number. Okay, let's go ahead and check ourselves. So we've got this information up here. Take a look at this guy. If you had a solution with one times ten to the negative, a one times ten to the negative four molar solution of an acid, where's it going to go on the pH scale? It's easy. Once you've got this pattern, once you see the pattern, it becomes easy. What about this one? One times ten to the negative twelve. Where would you put this one? We don't have a box already in place for that, but it's got to be somewhere on the basic side of things, wouldn't you say? And what's the pH of that one times ten to the negative twelve? What would you say the pH of that is? Easy. It's twelve. Let's put it as twelve. Okay, hopefully this activity that you just did helps you understand why the pH scale acidic pHs are low numbers, but they indicate high concentrations of hydrogen ions. I'm not kidding. How long have I been teaching and how many times have I taught this right here? Many, many, many and long, long, long. I have to think it through every time. I do and I often draw myself a picture. I'll draw like, oh, high hydrogen ions in acid. Yes. Okay. Because it's hydrogen ions are what causes it to be acidic and I walk myself through it and then I can match up the numbers, the pH numbers with what I would be expecting. So this is a counterintuitive thing, but hopefully this little activity assisted you. Now where are we going next? Biomolecules. It's time for us to look at biomolecules, which is great because pH changes the shape and function of biomolecules.