We're talking about this last property of water, the fact that water tends to dissociate into ions. Remember that dissociate means to break apart. And we looked at a more simplified version of this.
formula. We looked at water dissociating into hydrogen ions and hydroxide ions. And do you recall which ions make a solution more acidic?
So this is what's going to make a solution an acid, when more of the H-plus ions are free in the solution. So when the concentration of the hydrogen ions is greater than the concentration of the hydroxide ions in the solution, that's what we call an acid. When the hydroxide ions are higher, that's what we call a base. And when these two are equal, recall that's what we call a neutral solution. And this is the basis for acid-base chemistry.
scale which goes from 0 to 14 so 14 is going to be a very very strong base one is going to be a very very strong acid so remember that anything below pH 7 is an acid anything above pH 7 is considered a base pH 7 is considered neutral So if we added acid to water of any type, any type of acid, not any type of water, but if we added any type of acid to water, it's going to tend to break down into these hydrogen ions. adding a base to water is going to tend to dissociate into these hydroxide ions. How does the body deal with this?
How does the body deal with reactions that release more hydrogen ions into the blood? blood or extracellular fluid or inside the cell, how does it deal with the opposite situation? Well, we have something called buffers in the body.
And buffers serve to keep pH relatively constant for whatever the normal pH is in that environment. So buffers don't really serve to keep pH at 7. Buffers serve to keep pH at 7. To keep pH relatively constant, they keep it normal for whatever normal is for that environment. So the pH of the stomach obviously is significantly lower than the pH of the blood.
So the pH of the blood is about 7.3 to 7.4. The pH of the stomach... Thank you.
might be pH 1 to 2. So the role of buffers is to keep pH constant for whatever normal is in that environment. The way buffers work, it's usually called a buffer system. Because buffer systems can... Adjust regardless of what the situation is. In other words, if it becomes too acidic, the buffer system will shift one direction, and if it becomes too basic, the buffer system will shift the other direction.
What do I mean by that? Here's a very basic example of that. No pun intended.
It's not necessarily basic. So this would be the buffer with the hydrogen ion attached. And now this is going to be the buffer with the hydrogen ion released. There's something I need to tell you about chemical equations. I'm just going to give you a really basic chemical equation to start.
This is just kind of a little side story so you understand the formula for these buffer systems. And this is something we haven't talked about yet in this course. So I'm just going to write a basic chemical equation.
I'm going to write the basic equation for salt respiration. Okay, so two things you should note right away. Remember that when a number is written as subscript... That only applies to the preceding atoms.
So this would be saying we have six carbons, not that we have six hydrogens. We have six carbons, twelve hydrogens, six oxygens to make up this one glucose molecule. This, on the other hand, this six is telling us we have six O2s. It doesn't mean we have 12 oxygens bonded together. What it's telling us is that we have six of these.
This arrow is showing you the direction in which this reaction is proceeding. Everything to the left of the arrow is considered a reactant. So these are the reactants. and everything on this side, these are the products.
This arrow is telling you this reaction proceeds in this direction from reactants to products. Something else you should note is that in every single chemical reaction that takes place, the number of atoms on this side of the arrow has to equal the number on this side. We're not creating or destroying matter. We are simply breaking atoms apart, rearranging them to form different molecules. But all the atoms are the same.
That's pretty amazing because if you think about it, Glucose and oxygen are very different from carbon dioxide and water. In fact, I can get energy from this glucose. I can't get energy from carbon dioxide and water.
So while they are very different once you rearrange those atoms, the number of each type of atom on each side is the same. So let's look at this. Carbon, hydrogen, and oxygen on the left side of the arrow. Carbon, hydrogen, and oxygen on the right side.
This is a good practice in counting the numbers of atoms we have on each side of the arrow. Okay, so I have 6 carbons, I have 12 hydrogens, and I have 6 oxygens. And then here I have 6 times 2, which is 12 oxygens, so 18 total. So let's go to this side of the arrow.
Even though carbon dioxide and water are very different from glucose and oxygen, the number of each atom should be the same. Six carbons. Remember, it's imaginary parentheses here, so this six applies to the carbon and the O2s that are bonded together. So here we have six carbons, 12 oxygens. Here I have six times two, 12 hydrogens.
And six oxygens. So 6-12-18, 6-12-18. They're equal.
Sometimes we have reactions that can move in either direction. They're reversible. And reversible reactions are shown with a different type of arrow.
In a reversible reaction, we might just have some imaginary atoms here to show this example. This would be reversible. So depending on which way we're going, the reactants are going to be on one side of the equation, on one side of the arrow, and then the products will be on the other side.
Okay, so now let's look at an actual real buffer system, not just a cartoon buffer system. Let's look at a real buffer system. We're going to look at the carbonic acid buffer system as our example.
The carbonic acid buffer system is one of many important buffer systems in the human body. And it's a very good example of how buffer systems work. Okay, so this is the big formula for the carbonic acid buffer system.
Carbonic acid is going to form from carbon dioxide and water. But I'm only going to talk about this part of the equation. So, H2CO3, and now these are our reversible arrows, meaning this reaction can proceed in either direction, not just one direction.
Okay, so here are my two hydrogens. Two hydrogens. This becomes an ion, and this becomes an ion when they separate. This, you wouldn't know if this was an acid or a base. It's really irrelevant.
What's significant is that when we go to this direction, hydrogen ions are now free in the solution. And do hydrogen ions make something more basic or more acidic? Hydrogen ions make something more acidic.
This is what makes something an acid. So when we move this direction, we're making this solution more acidic. Is the pH going to go up or down? The pH will go down. So when would we want the pH to go down?
Well, when the pH gets too high. So if the pH in your blood gets too high, you would want to release some hydrogen ions to bring that pH back down again. So when pH is too high, in other words, too basic. If the pH becomes too basic, we want to release some hydrogen ions to make that solution a little more acidic and bring the pH back down to normal.
When it gets too acidic, we want to tie that acid up again. So when that acid is bound to another molecule or to other atoms, when it's not free in the solution, it's not acting like an acid anymore. Okay, so imagine that this marker is the HDO3 part and this is the hydrogen ion part. When this is free in the solution, it's making it an acid.
When it's attached, no longer an acid. So removing this lowers the pH. Putting these back together increases the pH. So when the pH gets too low, we want to shift back the other direction. So when pH is too low, in other words, too acidic, we're going to shift back this direction.
Okay, again, one more time. Here's our H2CO3, not an acid. When this H plus is free in the solution, it's going to make it more acidic. It's going to lower the pH. Put them back together, we increase the pH. This is a little bit complicated. If you don't understand that story, please rewind and listen again.
Just a couple of quick review questions. But before I do that, I just want to remind you of the properties of water we've now covered. Remember that water has a high specific heat and a high heat of vaporization. This is how water is going to moderate temperature change. Water has these two important properties, cohesion and adhesion.
Water molecules stick to each other via hydrogen. bonds and stick to other molecules and surfaces via hydrogen bonds. That's how we can pull water up a tube.
That's how fluids can move through living systems. Solid water is less dense than liquid water. In other words ice floats. Water is an excellent solvent meaning solutes dissolve readily in water.
Water shapes nonpolar molecules. We looked at that in particular with phospholipids and remember that's how cell membranes form. important concept.
And then lastly, water dissociates into ions and this is the basis for acid-base chemistry. So which pH value represents a very strong acid? So remember, higher the number over 7 is basic, below 7 is an acid, so the lowest number you could get would be the strongest acid.
So the correct answer is 1. 1.0 would be the strongest acid. acid of those listed. 14.0 would be the strongest base. Okay, 7 would be neutral. 5 would be a somewhat weak acid.
9 would be a relatively weak base relative to 14. How do buffers keep pH relatively constant? Remember, buffers are not trying to keep pH at 7. In fact, if your blood gets to pH 7, that's way too acidic. We want it to stay normal.
is for that environment. So how do buffers keep pH relatively constant? By being able to shift in one direction or the other to either release hydrogen ions or tie them up. Releasing them to make it more acidic when the pH gets too high, tying them up when the pH gets too low. If you have any questions about that, please rewind the video and watch that part again.
We're going to now start talking about organic chemistry in the next unit.