This eighth-grade science lesson is about chemical compounds. It is the 10th lesson in a sequence of 12 lessons on salts. The lesson is 45 minutes in duration. There are 30 students in the class.

00:00:14Good afternoon, boys and girls. Have a seat.
00:00:25Even though we have had this subject for a short time.
00:00:29We have done a few lessons. We've already discovered some things about chemistry.
00:00:42We've learned something about chemistry. What exactly is chemistry, youngsters? Evo?
00:00:47It's a science, which is studying substances and their transformations.
00:00:51It's transformations and compositions. Correct.
00:00:54And later on in the other half of today's lesson, we'll get to it. We will get to the fundamentals of the chemically pure substances.
00:01:03We also discussed mixtures right? What are mixtures? Don't be afraid.
00:01:10Mixtures are substances composed of different components.
00:01:12Yes. Mixtures are matter of different components. What are the ingredients?
00:01:19So, it's your turn.
00:01:20They are chemically pure matter.
00:01:21Yes, they are chemically pure matter. How are chemically pure matters distinguished?
00:01:24By the values of the physical variables.
00:01:26By the values of the physical variables. What kind of value of physical variables do you know of? Yes?
00:01:30The boiling point, the melting point, and the density.
00:01:33The boiling point, the melting point, and the density. Those are the three most important quantities. Correct.
00:01:39Good. And, I'd like to go back to the mixtures for a bit.
00:01:45I'm going to make some mixtures here, and you are going to identify them and characterize them as well. So, let's begin.
00:01:57Here is white chalk, which is used in school. I'll combine it with the chemically pure //distilled water.
00:02:06//Distilled water.
00:02:07What is the distinguishing characteristic of distilled water?
00:02:10It consists of pure water molecules.
00:02:11It consists of pure water molecules. Very well. So it's just the chalk and water.
00:02:18I'll shake it, and watch what's going to happen.
00:02:23It's settling at the bottom.
00:02:25Yes, it's settling down. What kind of mixture is it? Homogenous or heterogeneous? Nicolo?
00:02:33Because we can recognize the parts of the chalk.
00:02:34Yes, we recognize the parts of the chalk, because they are way too-
00:02:40Great. So, that would be a suspension.
00:02:44Good, let's try another one.
00:02:49I'll take oil.
00:03:01So I have oil in there and let's put some water in it. I'm mixing it again and what do we see?
00:03:14So, all of you participate, don't be afraid. Veroniko!
00:03:15It is insoluble liquid matter in another liquid. Correct. So, that was another mixture. Let's try a new one.
00:03:16Emulsion. It's undissolved liquid matter in another liquid.
00:03:35I'll take a little bit of a soap and put it in the test tube. Again I'll add distilled water to it.
00:03:51And what is it?
00:03:55What is foam?
00:03:57It's a dissolved solid matter in, uh... dissolved-
00:04:02Think about it!
00:04:05It's dispersed solid matter...
00:04:10It's insoluble gas matter.
00:04:12Yes, it's insoluble gas matter in a liquid. Where do we come across foam on a regular basis?
00:04:21In the bathtub.
00:04:22More you play with it //the more foam you make.
00:04:24//More of the foam we have.
00:04:27Correct. Let's try something else.
00:04:33I have one matter here, you pay very close attention.
00:04:45I'll add a little drop, a little drop.
00:05:04What do you see?
00:05:07Yes, it's burning. We'll talk about it later, but what is this?
00:05:11It is smoke. What is smoke? I can see it clearly even though I put a little amount of it there, so we wouldn't get smoked out.
00:05:18It's insoluble solid matter in a gas matter.
00:05:21That's right. You are absolutely correct. Where do we experience smoke?
00:05:28Industrial factories.
00:05:30Of course. And we have a lot of trouble with it, because it's polluting the air and so on.
00:05:36So we have practiced some of the heterogeneous, heterogeneous mixtures. And I also wanted to show you one more thing.
00:05:48I have some blue vitriol here and you've seen it already, of course.
00:05:53But I'd like you to see the difference between what we just did and what we're about to do now.
00:06:06So, I'm putting the blue vitriol into the test tube, and I'll mix it with the distilled water again.
00:06:17I shake it up and now, everybody, watch the reaction. Look at the difference between this one and that one.
00:06:27Simon, can you see it here in the first row? Go ahead, please.
00:06:30What kind of mixture is this? We've already said that. You identified this correctly the first time.
00:06:34Correct. Can you see it? And why?
00:06:36Because we don't recognize the difference between the two components.
00:06:39We don't recognize the differences between the two components. Why not?
00:06:44Because they are not visible to the eye.
00:06:45They are not visible just to the eye because it's in what kind of form? You know that from your physics class?
00:06:50Atomic form.
00:06:53Possibly? Anything else?
00:06:56Molecules. Correct. Possibly the bigger molecules. So that is the basic difference between homogenous and heterogeneous mixtures.
00:07:06The purpose of chemistry and physics is to separate each component, so we can get to the chemically pure matter.
00:07:18Do you know some of the methods of separation of matter? You've seen some already.
00:07:21It is distillation. What is distillation?
00:07:23Only one student knows? That would be a shame.
00:07:27It's based on different-
00:07:29The boiling points.
00:07:31Temperatures at which ingredients boil. That's right. We've also paid some attention to the air.
00:07:36And we talked about the oxygen and //nitrogen and other gases which are made by distillation of liquefied air at its boiling point.
00:07:44Tell me some of the boiling points. Do you remember them?
00:07:47Nitrogen is minus 194 degrees Celsius.
00:07:51And oxygen is //minus 183 degrees.
00:07:53Yes. Another method of mixture separation //is crystallization.
00:07:59Look at this. You have already done it, and we talked about it during your laboratory work. And here I have little crystals of blue vitriol.
00:08:08I'd like to show you one important thing. I hope that I'll be successful. I want to show you a different kind of crystallization.
00:08:21I'll use a substance which you already know. It's naphthalene. And next, I'll take- I'd like to ask you first?
00:08:33Is naphthalene soluble? Do you remember? In water?
00:08:38In what is naphthalene soluble?
00:08:39In organic solvents.
00:08:41In organic solvents. Correct. So now, I put little bit of the naphthalene into the test tube.
00:08:54So far, I have a little too much of it in here, so I'll put that aside. I have to scoop it up again.
00:09:11So now I have the naphthalene in the test tube, and let's add the organic solvent.
00:09:26As you can see, the naphthalene is really dissolving, isn't it.
00:09:37Now, I'll take a Petri dish and we'll try something.
00:09:48So now you can see the reflection and I drop a little bit of the dissolved naphthalene- I'll put a drop in the Petri dish.
00:10:04And now, you can keep watching it.
00:10:16If anything is going to happen. So, keep watching it.
00:10:38So now you can see it. It's appearing in the reflection and everybody can see it. What do you see, //slowly?
00:10:47Yes. You can start seeing little crystals. It's quite fast crystallization and now I'll tell you why.
00:10:55When there is crystallization of blue vitriol, it takes a lot longer. Here, you see, I haven't raised the temperature at all.
00:11:03Because the organic solvent quickly-
00:11:07It evaporates quickly.
00:11:08Correct. It evaporates quickly and I think it's obvious that it was a successful experiment.
00:11:15So that's information regarding the mixtures.
00:11:20One of the most important mixtures- the mixtures for our survival is for example-
00:11:25That's not a mixture.
00:11:27Water, good. And also the other gas mixture?
00:11:32It is the air. Can any of you tell me- we have little time for this. Can you tell me, what kind of ingredients are in the air?
00:11:40So, Ivono, I think you know this stuff very well today. Please, go ahead.
00:11:43So argon, neon, nitrogen, oxygen, sodium, helium, krypton, cobalt and-
00:11:53No. Definitely not the cobalt.
00:11:55But it's 78% nitrogen, 21% oxygen //and the rest is inert gases.
00:12:03Inert gases. Now, we're not going to discuss any details, but I'd like to show you three different types of gases.
00:12:12And you should be able to recognize them and characterize them. So I'm going to start now.
00:12:23So into this test tube, I'll put-.
00:12:35Potassium permanganate, yes.
00:12:45So that's enough. I've put calcium carbonate in this beaker. I'm only going to tell you that it's a marble. It's calcium carbonate.
00:13:01And in this test tube, I have hydrogen. I'm sorry, it's zinc. I apologize. It's zinc. And now we'll watch the reaction.
00:13:11I'll put hydrogen chloride into the first beaker. And I'd like you to notice that the dishes are set next to one another.
00:13:31So I added hydrogen chloride to that, okay? Look at it.
00:13:37Here, I have that potassium permanganate, and I'm going to warm it up.
00:13:52So now, I'll take... okay? We can turn this off and you can see the crystals here, okay?
00:14:07So now we're going to take a look at the changes. Here you can see that it's effervescing and foaming.
00:14:28I'll put it in this first beaker. It's burning.
00:14:34It died immediately.
00:14:35The nitrogen.
00:14:38You could be correct because you're not so familiar with chemistry yet. It definitely shut down the flame.
00:14:43So we know that there is a passive component of the air which doesn't support the burning. I completely agree.
00:14:47But I've told you kids, that I put calcium //carbonate in there. So I think that should help you little bit.
00:14:52//Calcium carbonate.
00:15:00So now, I'm going to do something different.
00:15:06We have to wait little longer. It's already visible even if this wasn't very successful. Did you see how it flamed up?
00:15:20Now, it's more obvious, okay? There is a substance, which is-
00:15:26Supporting burning.
00:15:27Yes, correct, it supports burning. So what is it going to be?
00:15:31Yes, it's oxygen. And some of you already realize that the previous element wasn't nitrogen because I'm not able to create it here.
00:15:36Carbon dioxide.
00:15:37It is carbon dioxide. Vero, could you possibly characterize the oxygen, please?
00:15:40It is heavier than air and it's non-reactive, and it's (inaudible) and it's suffocating the flame. It's a passive fire extinguisher.
00:15:50Yes, it's also used in fire extinguishers. Correct. And oxygen is an active air component- let someone else answer the question. So you go ahead.
00:16:03Where and what for, do we use oxygen?
00:16:08For welding metals and cutting //metals.
00:16:09//For welding and cutting metals. Oxygen- acetylene, oxygen- hydrogen flame. Correct.
00:16:14And now I'm going to add little bit of hydrogen chloride into the zinc. So.
00:16:26From the layout of the beakers, you could've realized- when I left it out here, that-
00:16:34That oxygen is heavier than-
00:16:35Than the air and over here-
00:16:36The same. //It's also heavier.
00:16:38//Also. And here you can see that I have a little different position, and I have to let it sit for a while.
00:16:43(inaudible) It's very light.
00:16:45Yes, yes, that's correct. It's the lightest-
00:16:51//Gas. Correct. What was the hydrogen used for? I've said used.
00:16:55In airships.
00:16:56Why can't we use it anymore? I think it's obvious.
00:16:59Because it's explosive.
00:17:00Yes. It's very explosive. I've also said, that it's going to be hydrogen, so let's prove it.
00:17:12And because we're running out of time. What time is it?
00:17:21Nine twenty.
00:17:22Nine twenty, great. So soon enough we'll move on.
00:17:34So, let's see if it's there.
00:17:37Yes. So, we will pay attention to this a little more.
00:17:41First of all it was a little explosion and the second part is, who watched it carefully see, that the test tube got //foggy.
00:17:48That means, there is-
00:17:52Because hydrogen was combined with oxygen, and we've got water. Water. Good. Now, we're going to pay attention to a new subject.
00:18:01Because, to my knowledge, you covered this very well. So again, what do I have here (inaudible)?
00:18:08Distilled water.
00:18:09Distilled water. Distilled water. It is-
00:18:14Chemically pure.
00:18:15Correct. It contains only... Don't be afraid.
00:18:17Water molecules.
00:18:18Molecules of pure water. That means that the basic building blocks of chemically pure compounds are-
00:18:27(inaudible) The molecules.
00:18:29The molecules. And now, please take your notebooks and write it down.
00:18:52The subject of today's lesson is elementary composition of matter. Elementary composition of matter.
00:19:16As you formulated correctly, the basic building blocks of compounds are molecules. By the way, I think you should know that from physics.
00:19:26So, the building blocks of compounds are molecules... are molecules. The building blocks of compounds are molecules.
00:19:56And of course, we mean chemically pure compounds.
00:20:02And today, we're going to pay attention to the typical characteristics of matter. Let's try it out. I'll take another Petri Dish.
00:20:22And I'll take chemically pure water again and-
00:20:39Now, I'll take the different matter which is the organic matter. It's called camphor. Camphor is very light and that is its typical quality.
00:21:02So, I'll put some of it there and add little bit of water.
00:21:15I have to remind you that it's distilled water.
00:21:21And again, I'll turn on the overhead projector and now I'll put down little bit of the camphor. You can probably see it.
00:21:40And now you know it from physics, and I'm glad I can continue on that-
00:21:43It's Brownian motion.
00:21:45Yes, there is water, molecules of water, nothing else. We also have the camphor there and like you've said, it's Brownian motion.
00:21:59Mr. Robert Brown was observing this motion in a slightly different form in the year 1827 when he observed- you might know.
00:22:07He observed pollen and water.
00:22:10Yes, water and pollen grains. He was a botanist and he observed water and pollen grains. And, all of a sudden, he saw this movement.
00:22:20Originally, he thought that it's done by some vital force, by vitality of the pollen.
00:22:27But because he was a scientist, he knew that in chemistry, physics, and any other natural science, you need to do a controlled test.
00:22:32So he did it. And instead of pollen grains, he used a printer's ink, and he got the same reaction.
00:22:41So now we understand Brownian motion. What is hitting the molecules of camphor? What is pushing it?
00:22:46Molecules of water.
00:22:48There are molecules of water. Yes, molecules of water. So the first basic quality of molecules is?
00:22:57Chaotic movement.
00:22:58Yes, and its chaotic movement. Very well. Random. So now we're going to write it down.
00:23:33Yes. So Brownian motion is constant and random movement of molecules.
00:23:49And now we're going to investigate...
00:23:55How molecules move in different environments. I'm going to use the environment of the classroom. Pavel, what is it?
00:24:11Great. So I'm going to use what state of matter?
00:24:15Gaseous state. I'm going to use //liquid state as well.
00:24:18//Liquid state.
00:24:21And I'm also going to use some kind of unusual state of matter which I made before. It is a thick gelatinous matter.
00:24:34So, let's begin. First of all, gaseous matter. And watch.
00:24:44By the way, what is it?
00:24:48Fog, yes. Great. It's an aerosol. It's a fog. And look at this. And now use your other sense.
00:25:03Is it done?
00:25:05Not yet.
00:25:07Good. You are resisting; I know you. Here, I have water.
00:25:17And on the top of the test tube with water, I put nothing else than filter paper. And I'll add to it, something we've already used today...
00:25:36Potassium permanganate.
00:25:47Now, you're going to watch it. I'll add little bit of water.
00:26:09And keep watching it.
00:26:13Girls and boys, I have four complex chemical compounds here for you. They are salts of heavy colored //metals.
00:26:27We don't really care about the names at this point. I'll show it to you later on, but first, I need to put it there.
00:26:33Here, I have the thick, very thick solutions. Can you see it? Yes, it is the gelatin. I put iron trichloride into one of them, for example.
00:26:51Iron trichloride. Later on, I'll show you that closer.
00:27:02Into the second one, I put nickel sulfate.
00:27:15Here we go.
00:27:25Yes, I put it here. Into the third one, I put copper sulfate.
00:27:47For example into the next one I add copper nitrate. Look at this- beautiful blue crystalline matter.
00:27:59Girls, wouldn't you like that?
00:28:08And now, I let it react, kids.
00:28:14So, we do a lot of it together, but you can see the great penetration. Are you able to see that the potassium permanganate-
00:28:27And here I take it, so you can see it better. It's much slower even though here you can see //the penetration.
00:28:43In this kind of experiment, the waiting period is 24 hours. Of course we're not going to wait that long.
00:28:50But still today, after the break, you should come back and check out how far the penetration went. Here, you can see it very nicely.
00:29:00But I wanted to get one thing out of it. In what kind of environment did the molecules expand the fastest?
00:29:08In liquid.
00:29:09No. In gas.
00:29:10In gas, correct. It was very obvious. The next one was //liquid matter.
00:29:12//Liquid matter.
00:29:16And the slowest one was in the thickest environment- gelatinous matter.
00:29:21In the solid state, absolutely solid state, penetration is very, very slow, almost none.
00:29:41The penetration of molecules from one substance into another substance. Not "into another" but between the molecules of another substance. What is it called?
00:29:53Does anyone know? This effect is called? Ireno? //You should know it.
00:29:57//Diffusion. Diffusion.
00:30:00Yes, it is diffusion.
00:30:02So diffusion is penetration of molecules of one substance- But be careful. Not the molecules into another substance, but between the molecules of another substance.
00:30:13I told you to pay attention to this experiment because I did something very different with this potassium permanganate.
00:30:23I warmed it up and the potassium permanganate started //cracking, yes. There was some releasing of water.
00:30:32But most definitely, the potassium permanganate was decomposing because there was the formation of oxygen.
00:30:36So that means that it was a chemical change. A new chemical substance was formed.
00:30:39And I'm asking you: Is this a chemical or physical change?
00:30:44Chemical, physical.
00:30:48This is maybe a bit difficult for you, but one more time. This is all, obviously, a chemical //change. There is a formation of new substances.
00:30:52//Chemical change.
00:30:55This is a //physical change.
00:30:57//Physical change.
00:31:00The base of potassium permanganate //is not changing.
00:31:03//Is not changing.
00:31:04So please, write it down. Diffusion...
00:31:28It is the penetration of molecule one of one substance...
00:31:35Between molecules, molecules...
00:31:46Of different matter.
00:31:51Between molecules of different substances.
00:31:58Between molecules of different substances.
00:32:05So the fastest one, like you've said before, is //gaseous state.
00:32:09Just for your interest, I'm going to mention that the speed of the hydrogen molecules- the lightest element- is fantastic.
00:32:16It is around seven or eight thousand kilometers in one hour. The speed of molecules of oxygen is 1,800.
00:32:27Molecules of carbon dioxide, which we made here is 1,200 kilometers in an hour.
00:32:34Please, tell me.
00:32:35Why are the molecules of hydrogen the fastest, molecules of oxygen slower, and molecules of carbon dioxide the slowest?
00:32:41Only two of you? It should be more of you. So, Simone, try it.
00:32:46The hydrogen is the lightest.
00:32:48Hydrogen is the lightest element. It has the smallest molecules, yes. After that is oxygen, after is... good.
00:32:55So write it down. You can do it by yourself. I'm just going to dictate. The speed of movement of molecules...
00:33:12The speed of movement of molecules is the fastest...
00:33:24In a gaseous state.
00:33:35A dot. In a gaseous state.
00:33:47Good. Some of the molecules are very simple, and some of them are very difficult.
00:33:54Can any of you draw some simple molecules on the blackboard? Don't be afraid. Come here, take a chalk. You can choose a color.
00:34:08It depends on what you're going to draw, good. Come on.
00:34:14Some of the molecules are very simple. Today we prepared hydrogen and oxygen.
00:34:24So, yes.
00:34:34What does the one blue... mean? One blue circle?
00:34:41An atom.
00:34:42Yes, it's an atom. Great, Simone. What did you draw there exactly? Tell us something about that in your own words. Don't worry.
00:34:50It's oxygen.
00:34:51Yes, an atom of oxygen.
00:34:53Plus oxygen.
00:34:57A molecule of oxygen.
00:34:58So you can see that an oxygen molecule is very simple. It has two atoms. Can somebody draw a hydrogen molecule?
00:35:03Come on up. You can sit down, Simone. Very good job.
00:35:14And, Nikolo, you can try to draw the water molecule. Let's go.
00:35:33So you put it together this way. I agree.
00:35:36And we talked about how water originated on our planet. Does anyone remember that?
00:35:43(inaudible) No, no. The Earth came from the universe. There was water, air, and bacterial substances. Water and air formed condensation.
00:35:49Condensation is the compounding of molecules of hydrogen and oxygen and water. This creates clouds, which result in rain.
00:35:58Yes. So, simply put during the condensation.
00:36:01And Norbert is trying to outline, at the board, what is being said.
00:36:06What does it mean? Please explain.
00:36:08One atom of oxygen //plus two atoms of hydrogen is a molecule of water.
00:36:11//Yes, we can-
00:36:16The molecule of water. So, kids. Some of the molecules are very simple. Some of them are very simple.
00:36:24For example, you saw- I don't know where I put it now, but that's not important now. A solution of blue vitriol.
00:36:32Or here, you can see the solution of potassium permanganate. But I'll show you at the end of today's class that some of the molecules,
00:36:41Are very complex. These are primary molecules that can be found in natural substances. I have a simple egg here.
00:36:55And girls should help me now, girls. And I'm trying to do one thing.
00:37:07And I'm separating-
00:37:09Egg yolk from the egg white.
00:37:10Not very successful and yet I've done it all right. So I separated the egg yolk from //the egg white.
00:37:22//From the egg white.
00:37:24Correct. So now, I have the egg white here. What state of matter is it?
00:37:33It's a liquid.
00:37:34Yes, it's a liquid. That means that it's a //solution.
00:37:42Solution. But be careful. Look at this solution and look at this one as well.
00:37:50Well, the egg white is denser than the other one.
00:37:53It has higher density. I agree. But if you again look at this solution, is it clear or it is not?
00:38:08It is cloudy.
00:38:09It is cloudy. It's cloudy. This cloudiness is called opalescence in foreign terminology. It is cloudy. Do you know why it's cloudy?
00:38:23Why is this one clear even though it's colored?
00:38:28It didn't change (inaudible).
00:38:29No. It's not because of that, but why? We've said that homogeneous mixtures are the kind of mixtures... yeah...
00:38:45where we do not recognize each... Ok, I'll finish this myself... each ingredient. Because in another form are molecules.
00:38:53The molecules are so little here, so we can't see them.
00:38:56But here in the complicated organic compounds, the molecules are so small, so we can't see them with the naked eye.
00:39:06But they are so big that they reflect //the light. So that's why we have the cloudiness here, and that's why we have the opalescence.
00:39:10//The light.
00:39:17We call this a colloid solution. A colloid solution, or different name, is a false solution. All right.
00:39:28Some of the molecules are so big that they can reflect the light. How do you translate big in a different language? It's a prefix.
00:39:41It's in German.
00:39:43That's good. I'm glad you know it in German. So, small- Let's do it this way: One meter, one thousandth of one meter is?
00:39:55Milli, mega. Well. Well.
00:39:58Milli, milli, small is milli, milli, milli.
00:40:02Yes, it could be mega. And here it is macro, so I'll finish it myself so we can finish the class on time. Macro.
00:40:07You know the huge supermarkets, don't you? Macro. That's why we call it macro. So these are macromolecules.
00:40:18So now, let's write it down: Some of the molecules are simple. They are simple.
00:40:44What kind of solutions do they make? The ones where we do not recognize, these solutions we call the true simple solutions. Simple molecules create true solutions. You already know the symbol for solution, don't you? So, the true solutions.
00:41:01Some of the molecules are simple, true solutions.
00:41:07Some of the molecules are complicated, big. We call them macromolecules. Macromolecules, big, complicated.
00:41:37Macromolecules, macro, big, kids write it down. Macro.
00:41:49And they make colloid solutions... colloid solutions.
00:42:07And we have to mention that they are mostly natural substances.
00:42:16So now, I'm going to write it over here. You're going to continue under... mostly natural matter, natural matter.
00:42:27What kind of natural matter, for example, did you see here? The one what makes a colloid solution?
00:42:34Yes. That is true, Petre. But I mean the colloid solution.
00:42:37The egg white.
00:42:38The egg white. Yes. So proteins, for example. So I'll write it down. Proteins.
00:42:46And in today's life, they come into our lives more and more. And what about these substances? Like I have it right here.
00:42:56Yes, it is plastic. Plastic is also formed by macromolecular matter. So now we're going to add it there, plastic.
00:43:13And so on-
00:43:21So, girls and boys, have you finished writing it down? So today we repeated mixtures, some substances. For example, oxygen, hydrogen.
00:43:30Next we talked about new substances, like molecules and their unsteady and random movement.
00:43:40And then where the movement is the biggest, the fastest, the smallest. And next, we discussed the true solutions and colloid solutions.
00:43:50I'd like to say that you worked very well. I won't have time right now to go around and look at your work, but I pretty much know how you work.
00:43:58So at the beginning of the next lesson, I'll go over that and grade your work. We'll consider today's lesson as a little oral grading. Yes.
00:44:08We'll do the grading later. Please, take out your textbooks. The big new books on pages 20 and 21, please.
00:44:25And you have a section there-
00:44:29Why didn't you excuse yourself?
00:44:30I forgot.
00:44:31You forgot again. All right.
00:44:37So, pages 20 and 21. So, on pages 20 and 21, you have an article about the things I was talking about.
00:44:49Everything I've mentioned today is in this section here. And we finished on the page 21 at the macromolecules, right here.
00:44:59Okay. So that was good timing. And next time, you're going to know something about molecules.
00:45:08And I'll come back to the grading of your work. That would be all.
00:45:26You can leave now. Bye.