NL1 SUSPENSION AND EMULSION
This eighth-grade science lesson is about suspension and emulsion. It is the second lesson in a sequence of eight lessons about the properties of water. The lesson is 42 minutes in duration. There are 24 students in the class.
| Time | Caption |
|---|---|
| 00:00:17 | Are we complete or is anyone missing? |
| 00:00:28 | Guys, are we missing anyone? I don't think so, right? |
| 00:00:30 | No. |
| 00:00:42 | Okay. Last time we did experiment A and B, boiling water. And we examined whether certain substances dissolve in certain solvents. |
| 00:00:59 | And I'd like to discuss these experiments, like I did briefly last time at the end of the lesson. But let's get back to it for a moment. |
| 00:01:11 | Good, the idea of doing a test is to experiment and to examine if the present theory still holds. |
| 00:01:20 | And in case there isn't any theory yet then you could create one yourself, right? |
| 00:01:23 | Now, determining the boiling point of water, that's not too complicated since it's well known and has been tested many times. |
| 00:01:32 | So as far as that's concerned we're not dealing with high tech research here. |
| 00:01:35 | But the idea is rather that you grow accustomed to using a burner again and practice with it-how to read a thermometer, |
| 00:01:44 | Uh, and what Paracelsus said, right? What did Paracelsus say? |
| 00:01:50 | Me? |
| 00:01:52 | Yes. |
| 00:01:53 | That you understand something by experimenting. |
| 00:01:58 | Precisely, and so //don't reason- |
| 00:01:59 | //And tear up your books. |
| 00:02:00 | Tear up your books because all they contained was? What was the only thing they contained? |
| 00:02:04 | Facts. Arguments. |
| 00:02:05 | Arguments. Things that were made up but that were not tested by measurements. So we're just going to test them! |
| 00:02:14 | And I already heard some say, "Yeah, but we already know that the boiling point for water is 100 degrees." |
| 00:02:18 | Well, go ahead and measure that to see if that is indeed the result, whatever the book says. And we've seen some differences already, didn't we? |
| 00:02:24 | Not everybody had measured 100 degrees. The reading of the thermometer was already where it started to go wrong. |
| 00:02:31 | So that's what I'd like to address for a moment. |
| 00:02:33 | (inaudible) is broken. |
| 00:02:34 | That can happen as well. If you have a boyfriend or a girlfriend who works in a job and you ask, "How much do you earn?" |
| 00:02:45 | And, he says, "Well, I earn ten. Ten guilders." |
| 00:02:51 | And you ask another friend who does exactly the same work and earns the same amount and the answer is, "Ten twenty-three per hour." |
| 00:02:59 | They don't earn the same. |
| 00:03:00 | No. |
| 00:03:01 | (They have the same job and they earn the same.) |
| 00:03:04 | They say something different but they earn the same amount. Now what's more precise? |
| 00:03:09 | The one on the right. |
| 00:03:10 | Please raise your hand if you know it... go ahead, Ronald. |
| 00:03:13 | The one on the right. |
| 00:03:14 | Why? |
| 00:03:15 | Because there are more (decimals). |
| 00:03:17 | Exactly. The more decimals, the more precise it is. With the ten- the ten guilders, |
| 00:03:25 | Perhaps he earns, what shall I say, ten point fifteen, but that would be rounded off to ten guilders. |
| 00:03:33 | Or maybe he makes nine guilders ninety per hour, but if I go round that off into a whole number, then that's ten as well. |
| 00:03:41 | Therefore, the more numbers behind the point the more precise. Well, this doesn't only apply to money, it applies to everything you measure. |
| 00:03:47 | When I want to read a thermometer. |
| 00:03:55 | Presume 99 is here, and here's 100. |
| 00:04:01 | And the liquid in the thermometer reaches exactly halfway. What do you say then? What do you read in this case? Sandra? |
| 00:04:12 | Ninety-nine point five? |
| 00:04:14 | Ninety-nine point five. So you're here, you want to read it and it's 99.5. |
| 00:04:21 | True, there are no measuring stripes in between here but you can make an estimate, right? |
| 00:04:25 | These stripes have such a distance in between them that you can see whether you are on the 99, 100, or somewhere in between. |
| 00:04:32 | But you may not be able to see exactly if it's 99.4, or 99.5, or six. So you make an estimate. |
| 00:04:41 | So by presenting it with one extra decimal, we can be more precise. |
| 00:04:52 | Well, what else do I see going wrong? Here is the 90- oh, no, the 99- and here the 100, and he'll reach exactly up till here. |
| 00:05:06 | And then I see some of you write down 99 again. Why is that incorrect? |
| 00:05:13 | It has to say point zero. |
| 00:05:15 | That's right. You should add point zero, right? This way you indicate that you know it exactly up to one decimal. |
| 00:05:21 | Even though it's a zero, it does indicate the precision, doesn't it? So don't forget this. Each time you measure something- |
| 00:05:29 | No matter if it is a thermometer or a measuring cylinder, check to see if you can make an estimate of what's between the measuring stripes. |
| 00:05:38 | And show this in your answer. Indicate the accuracy, okay? |
| 00:05:43 | This time during the lab I have corrected it for most of you. But do you understand why it's like this now? Why it's good to read it this way? Yes? |
| 00:05:53 | Okay. So much for the thermometer. Then, we've discussed the deviations, right? |
| 00:06:06 | What could be the reason something deviates from what the theory says? Do you remember? |
| 00:06:12 | No. |
| 00:06:13 | No? |
| 00:06:14 | No. |
| 00:06:16 | If we measure something and the result is different from what we expected, then there's two things we can do. |
| 00:06:26 | We can try to find an explanation for this deviation, or we can try- we can say, "That theory is completely wrong. I think it should be this and that." |
| 00:06:37 | We are dealing with very slight deviations here, right. So in this case, we try to find an explanation for the deviation that we measure ourselves. |
| 00:06:46 | There are substantial differences between you all individually. One had 98 degrees, the other had something over 100, |
| 00:06:52 | One hundred and a half. |
| 00:06:56 | But, apparently, the theory says that the boiling point of water is exactly 100, one hundred point zero degrees Celsius. |
| 00:07:04 | Okay. Try to explain the deviation that you guys have found here. You are not allowed to write down 100 when you measure 98. Got that? |
| 00:07:12 | Write down what you measure. Loraine? |
| 00:07:16 | Can the (thermometer) be broken? |
| 00:07:18 | It can be broken, that's right. And what exactly do you mean by broken? |
| 00:07:24 | Because it doesn't reach to 100. |
| 00:07:28 | Yes... but something I noticed about several thermometers, and I'm not sure if that applies to your thermometers. |
| 00:07:34 | You'll have the liquid here. It reaches, for example, 98 degrees, but here above there was a little bit of that red liquid as well. |
| 00:07:46 | In fact, then that is still part of it, right? And that would, indeed, mean that it's broken. Was that the case with you guys? |
| 00:07:51 | Well, ours was constantly at 98 the whole time and then it went down to 97. |
| 00:07:54 | Yes, we had that too. |
| 00:07:56 | Yes... there is an explanation for that as well. What is- did you do something else when it was 98 and sunk back to 97? |
| 00:08:08 | I did something different with most of them. |
| 00:08:11 | I said, once it boils, the temperature isn't going to rise any further so there is no need to set that burner so high. |
| 00:08:17 | So I just brought the burner back a little bit- the airflow, you see- so that it started burning a little less violently. |
| 00:08:25 | We are going to take a more precise look at it now. I am holding the beaker here. Okay, the thermometer is in there with the top like this. |
| 00:08:35 | And over here I have... the burner underneath it. |
| 00:08:40 | That water, that can become 100 degrees at a maximum, right, according to the theory. So that's what we'll presume for the time being. |
| 00:08:48 | But the flame, how warm can that become? |
| 00:08:51 | Warmer. |
| 00:08:52 | A lot warmer, sure. It can easily become a couple of hundred degrees. That beaker, how warm could that possibly become? Yes? |
| 00:09:01 | (inaudible) |
| 00:09:04 | Much warmer, of course, than that water... Yeah, the melting point of glass lies somewhere beyond 1400 degrees, right. |
| 00:09:10 | So you need lots of heat, very special ovens in order to be able to melt it. Therefore, that beaker can also easily get warmer. |
| 00:09:20 | As long as that flame is warmer, it can get warmer here... If I put the thermometer mostly at the bottom here, |
| 00:09:26 | And it rests for a large part upon that beaker that gets so incredibly hot because I have that flame so high, |
| 00:09:32 | Then I'm actually not really acting honestly, am I? |
| 00:09:36 | Because, in fact, I'm not only measuring the temperature of the water, |
| 00:09:41 | but I am also measuring the beaker temperature of the bottom of the beaker, right? |
| 00:09:45 | So that could be an explanation why, in case you have this thing on really high ... |
| 00:09:50 | Why you could have read a higher temperature than those 100 degrees which I noticed was the case with some of you. |
| 00:09:55 | How could you avoid this? Lydia? |
| 00:10:00 | By holding the thermometer up a bit higher in the glass. |
| 00:10:04 | Correct. By making sure it's surrounded by nothing but water, right? Because the water can't get warmer. Some mentioned stirring. |
| 00:10:12 | Well, stirring matters mostly in the beginning. Because if I'm going to warm it up, where does it get warm first? |
| 00:10:18 | At the bottom. |
| 00:10:19 | Correct. That warmth comes from underneath so the water at the bottom here will become warmer than the water above. |
| 00:10:25 | But what you want is one and the same temperature. We had an expensive word for that. What was that again? |
| 00:10:34 | Homogenous. Homogenizing. It has to become homogenous. So you want all the qualities to be the same all over. That's what we call homogenous. |
| 00:10:48 | Okay. What could be a reason the temperature is too low? |
| 00:10:52 | (What do you mean by too low?) |
| 00:10:54 | Well, for instance, that you read 98 instead of 100. Ronald? |
| 00:11:00 | The burner isn't positioned properly. |
| 00:11:02 | Yes, exactly. The burner isn't positioned exactly, right. It might be slightly to the side. |
| 00:11:07 | If I see the way some of you guys do a lab, it's, in fact, a miracle that everything keeps standing up. |
| 00:11:11 | The wire gauze being all rounded instead of hollow, which makes it all very unbalanced, |
| 00:11:16 | Especially when it starts boiling and bubbling, you have to make sure it's all positioned steadily. That burner is sometimes put slightly sideways. |
| 00:11:22 | Make sure it's standing right underneath, huh? But what's also the case, what else did I tell you about those thermometers? |
| 00:11:29 | What were they made of in the past? |
| 00:11:31 | Mercury. |
| 00:11:32 | Mercury, right? And why don't we do that anymore? Jake? |
| 00:11:36 | It's dangerous. |
| 00:11:37 | It's dangerous, all right. Toxic. So we switched to alcohol-thermometers, and they just tend to be less precise. |
| 00:11:44 | Therefore, no matter how precisely you guys measure and how precisely you read, errors are going to pop up. System errors, we call those. |
| 00:11:52 | Errors in the equipment you use that cannot be avoided, no matter how well you do your best to be precise. |
| 00:11:59 | All right. We could focus on that in more depth, but that's not what we're going to do today. That's not what this is meant for. |
| 00:12:04 | I'd merely like to point out that when you measure something differently than what you would expect, then you're not gonna have to adjust it. |
| 00:12:11 | Like some of you did, as they had a tendency to write 100 everywhere. Like, "Sure, I already know what it is." |
| 00:12:15 | No, measuring is knowing. So even when it gives you something else than you expected, you are going to look for an explanation afterwards. |
| 00:12:23 | Good. Then we have tried to dissolve substances like sugar in water, and once sugar in alcohol. That was the second experiment, right? |
| 00:12:32 | Well, some did dissolve, and some didn't... What was dissolving?... Let's see. Ingrid. |
| 00:12:40 | That you cannot see the substance anymore. That you just see the water or the alcohol. |
| 00:12:46 | Correct. That it's divided so small that you do not see that solid substance. Or, alternatively, that liquid. Because you can dissolve those as well- |
| 00:12:51 | That you don't see it anymore. |
| 00:12:55 | What is then, um, what is a characteristic of a solution? That we cannot see it anymore... yes? |
| 00:13:04 | It changes... the color. |
| 00:13:06 | Not necessarily, the color doesn't have to change. If I dissolve sugar in water then it stays colorless, right? No color change. |
| 00:13:11 | We call that clear, right, the solution is clear. And what is clear? |
| 00:13:17 | //Not cloudy. |
| 00:13:18 | //Let's see. Not cloudy. |
| 00:13:20 | Ronald? |
| 00:13:21 | That you can see through it. |
| 00:13:22 | That you can see through it. That 's something else than colorless though, isn't it? If I look at tea for example, I can see through it. |
| 00:13:29 | It's clear, I don't see any solid substances left. Not even at the bottom. So it dissolves well. It's a solution, it's clear. |
| 00:13:36 | But it does have a color. It may be colorless, a solution, but it may also have a color. |
| 00:13:43 | All right. We have also made substances, or mixed substances together that didn't dissolve, can you remember? |
| 00:13:50 | Which experiment, what substances didn't dissolve? Lydia? |
| 00:13:55 | Chewing gum. |
| 00:13:56 | Chewing gum didn't dissolve. Yes? |
| 00:13:58 | Flour and chalk. |
| 00:14:01 | In what? |
| 00:14:02 | In water //and alcohol. |
| 00:14:03 | //Yes. Chalk in alcohol and chalk in water, it didn't dissolve. Yet we want to give this mixture a name. Does anybody remember what we called it? |
| 00:14:18 | Suspension? |
| 00:14:21 | We haven't gotten there yet. |
| 00:14:22 | Not there yet? Then I'll explain it to you now. All right. There are mixtures that do not dissolve. |
| 00:14:31 | And there are- and we can distinguish two different kinds of mixtures. One is a suspension, and the other is an emulsion. |
| 00:14:39 | Now what's the difference? In the case of a suspension we are dealing with a solid substance that doesn't want to dissolve. |
| 00:14:45 | For example that chalk in the alcohol, or um, for example sugar in the alcohol, or salt in alcohol... it doesn't dissolve, it becomes cloudy. |
| 00:14:55 | It starts floating through the liquid. And should you wait long enough, it will sink to the bottom, right? |
| 00:15:01 | Or an emulsion. And emulsion deals with two liquids... that don't dissolve into each other. So not a solid substance in a liquid but two liquids. |
| 00:15:15 | Okay, we're going to do an experiment with that, experiment 4C and 4D. I see that all the bags are put neatly at the side. |
| 00:15:23 | Um, you guys grab a plate, a coat, and a pair of goggles, that's all, and then you go sit down and you will get more explanation. |
| 00:15:29 | (Inaudible) |
| 00:15:33 | (Inaudible) |
| 00:15:35 | What doesn't it say anywhere, Danielle? |
| 00:15:37 | (That you have to take goggles). |
| 00:15:38 | That you have to take goggles? |
| 00:15:39 | Yes. |
| 00:15:41 | Yes? Is that what you wanted to say? |
| 00:15:43 | Yes. |
| 00:15:44 | No, but that is something we just do out of precaution. I don't want you to get any chemicals in your eye. |
| 00:15:51 | OHave they already, uh (inaudible)? |
| 00:15:54 | No, I haven't said, uh, anything about that yet. |
| 00:16:04 | These things are really dirty! |
| 00:16:05 | Dirty? But during summer break we have sent them all to the //laundromat. |
| 00:16:08 | O//Yeah. We've just washed them, dude. |
| 00:16:09 | But those are stains that won't ever come off again, you know. |
| 00:16:11 | This one is dirty as well. |
| 00:16:14 | This one is too large. |
| 00:16:15 | Right. Those can well be stains that will never come off anymore. That's the reason that you're wearing these, so that you will not get it on your clothes. |
| 00:16:20 | (I think this is size 48). |
| 00:16:24 | Yes, they tend to be kind of large indeed. Why don't you roll up your sleeves a bit. |
| 00:16:37 | (Do you have small glasses)? |
| 00:16:40 | Small glasses? Sure- |
| 00:16:44 | OYou have your coat on inside out. |
| 00:16:55 | OCome on you guys, hurry up a little! |
| 00:17:07 | OPut your coat on and sit down for a moment, then we'll explain what's the idea here. |
| 00:17:11 | That you still dare to wear a coat with that name on it, after yesterday evening. |
| 00:17:15 | Yeah, who would do a thing like that! |
| 00:17:19 | OYou're wearing yours inside out! |
| 00:17:20 | Ha, dope! Look! |
| 00:17:21 | OYou too! |
| 00:17:22 | Okay, //(inaudible). |
| 00:17:23 | [ laughter ] |
| 00:17:32 | OJust put your coat on properly. |
| 00:17:34 | Are you guys still getting dressed by your moms, or what? |
| 00:17:37 | (inaudible) How many dopes do you see here? |
| 00:17:43 | Look, you're starting wrong, you see? |
| 00:17:44 | [ laughter ] |
| 00:17:45 | Yes, what difference does it make which button is in //what hole? |
| 00:17:46 | //This way it's just sort of hanging here. //Look, here you're not matching ends. You have a button here but not there. |
| 00:17:49 | //Yes. |
| 00:17:52 | Dope! |
| 00:17:55 | Is that bad? |
| 00:17:56 | Go ahead and sit down, in your case it doesn't matter. |
| 00:18:02 | OSit down for a moment and listen to what the objective is. Experiment 4C and D, page 67. At 4C, at assignments. |
| 00:18:16 | OThe author of the book has, uh, forgotten one little line because at A it says: Put a spatula point of chalk in a test tube. |
| 00:18:25 | OWhich, by the way, we already have all set for us here, it already contains a bit of chalk. |
| 00:18:29 | OAnd then at B it says: Shake well, but that's of course not going to be any good unless you add a little water first. |
| 00:18:35 | OThat's what I mean. And when we talk about water in chemistry we always say: demiwater or distilled water. |
| 00:18:44 | OWhich is kept in those little bottles. And for B if you need lamp oil or dishwashing detergent than you can grab these things from over here. |
| 00:18:57 | OFor A you can find what you need over here- by the way you'll also need a little rack to put the test tube in. |
| 00:19:05 | OAnd if there are no questions then you can now start with A. Everybody keeps their goggles on though! |
| 00:19:12 | (inaudible) |
| 00:19:15 | (inaudible) |
| 00:19:16 | OThe racks are back there. |
| 00:19:19 | First a pair of goggles on and then you come get your things, //hey? |
| 00:19:21 | O//First put the goggles //on. |
| 00:19:22 | Yes, now I'm doing it correctly. |
| 00:19:28 | Miss? //And then you pick up your things, right? |
| 00:19:29 | //Yes? |
| 00:19:33 | Sure, because than you can get rid of them right away, you see? That's a lot more practical. |
| 00:19:37 | OGo ahead, go ahead and all three of you do B. //No, no (inaudible). |
| 00:19:39 | //(inaudible) |
| 00:19:41 | That's the next experiment, that's still coming up. |
| 00:19:49 | Who had the class folder, guys? |
| 00:19:50 | Not me. Not me either. |
| 00:19:52 | You? Ah. I have signed it already. so that you can bring it along right away, otherwise you might forget it later. |
| 00:20:06 | During this lab you may sit down. We're not working with a burner so you are allowed to sit down if you prefer that. |
| 00:20:13 | Ooh, How clumsily! |
| 00:20:15 | Yes. |
| 00:20:16 | Look, it's almost empty which makes it more difficult. If you hold it at an angle, then you are only squeezing a bit of air, right? |
| 00:20:21 | So hold it upright and as soon as it's no longer immersed you better refill it. |
| 00:20:26 | Do we shake it like this? |
| 00:20:27 | No, you were provided with a plug, weren't you? Because this way you'll get it on your thumb, you see, that's not allowed. |
| 00:20:36 | Do I have to add lamp oil //to this right away? |
| 00:20:37 | No. |
| 00:20:38 | No! //Read carefully! |
| 00:20:39 | //You've got to empty it out- |
| 00:20:42 | Oh, fill up with two centimeters of water. |
| 00:20:44 | Demiwater. |
| 00:20:47 | Oh, oh. You're lucky that it didn't break. |
| 00:20:49 | I've done that before. |
| 00:20:52 | OShake well... and read well what you're supposed to do! |
| 00:20:55 | Where do you have the chalk? |
| 00:20:57 | What chalk? |
| 00:20:58 | Didn't you have a test tube with chalk? |
| 00:20:59 | I threw it away. |
| 00:21:01 | Why? |
| 00:21:03 | It has water in it already. |
| 00:21:04 | So you want to get a new tube for that second experiment, or what are you doing? |
| 00:21:07 | Yes. |
| 00:21:08 | Ohh! You can also ask for a new tube over there, you know. |
| 00:21:11 | A new test tube? |
| 00:21:12 | Yes. |
| 00:21:13 | And look, rinsing, that's something we always just do with tap water, that doesn't matter. Only when we do a real experiment, then we get that water. |
| 00:21:18 | Would this be two centimeters? |
| 00:21:20 | Yes, but as you can see, there is still a little chalk in there, you see? |
| 00:21:22 | Here... here is a new test tube. |
| 00:21:24 | It's still slightly cloudy, see that? |
| 00:21:25 | What is the purpose of this cork? |
| 00:21:28 | Miss? |
| 00:21:30 | So that shortly you can shake it well. |
| 00:21:32 | (inaudible) we already had that, didn't we? |
| 00:21:34 | Uh huh. Yes, but you haven't had the concept of suspension yet and that's what this is about. |
| 00:21:39 | What kind of substance does not dissolve? |
| 00:21:41 | Yes. |
| 00:21:43 | And then the experiment is done? |
| 00:21:44 | And then the experiment is done. And you may start the next one. |
| 00:21:45 | (inaudible) |
| 00:21:50 | Do you need this for the second time again instead of (those over there)? |
| 00:21:52 | You can also get a new tube, there are plenty of tubes over there. |
| 00:21:55 | Yes, fine. |
| 00:22:01 | Do you have to, uh, get a new test tube then? |
| 00:22:03 | Yes, at the front are plenty of tubes left so you can go ahead and help yourself to //a new one. |
| 00:22:06 | //Yes, but this one is pretty clean. |
| 00:22:07 | No problem, in that case you use that one. |
| 00:22:11 | You know what I saw you doing just now, Sandra? |
| 00:22:12 | Yes? |
| 00:22:13 | You did it this way, didn't you? //I don't know how tight you fastened the plug, but it can't be too tight, right? |
| 00:22:15 | //Yes... yes. |
| 00:22:18 | Because then the glass would break so you just insert it gently but actually you should keep your finger on it just in case, yes? |
| 00:22:24 | Yes, okay. |
| 00:22:25 | Otherwise you'll end up with a little puddle here. |
| 00:22:28 | Right. |
| 00:22:33 | Um, I think we have to do our second experiment now. |
| 00:22:36 | With lamp oil and dishwashing detergent. |
| 00:22:39 | That's right. |
| 00:22:40 | Then we have to remove this- |
| 00:22:41 | Walter? |
| 00:22:42 | Yes. |
| 00:22:43 | Will you please start writing a little more neatly? It's totally illegible what is written here. |
| 00:22:47 | (inaudible) |
| 00:22:48 | Yes, really, I don't find it neat. It's impossible to read. Can you read this? |
| 00:22:56 | Well, I just happen to know, eh, what it's supposed to say, so - |
| 00:23:00 | Yes, look! Uh, no- [ laughter ] |
| 00:23:05 | Sure enough, that's okay if you guys see this... Look, if you know what it 's supposed to say then you get it, but I just find it too messy! |
| 00:23:11 | //No, it's beautiful. Look I can even read it upside down! |
| 00:23:16 | You can, but I cannot and I just want you to put more effort into your handwriting, just work on it, will you? |
| 00:23:23 | Yes, and I think this is very messy, too! |
| 00:23:46 | Moreover, I'm noticing that you haven't completed everything in chapter three yet. |
| 00:23:50 | What? |
| 00:23:51 | I'm seeing way too many empty questions in there. |
| 00:23:59 | This? |
| 00:24:00 | No, in chapter three. We have finished chapter three completely. But these questions here haven't been done yet, |
| 00:24:06 | This hasn't been done, this here, all open, here. |
| 00:24:09 | This here's a lab so at least you've written that down, but the homework over here, none of that has been done. |
| 00:24:18 | I suggest that this afternoon after school you'll come and sit with me for an hour and then you're going to work on it. |
| 00:24:24 | Because you're obviously not doing any of it at home, so you're going to do it with me. All right? |
| 00:24:31 | All right. |
| 00:24:32 | How many class periods do you have left today? |
| 00:24:33 | Uh, until... two o'clock. |
| 00:24:36 | Two o'clock. So at the seventh period you'll go over to room 64, okay? And there you're going to catch up. |
| 00:24:42 | Miss? |
| 00:24:43 | Yes? |
| 00:24:44 | Do you have to, over here, do you have to... do you have to (get) a new test tube? |
| 00:24:50 | Yes, go ahead and get a new one! |
| 00:24:52 | At least one, uh, (inaudible). |
| 00:24:53 | Get a new one because then you can compare it well. No! A new one! So you'll leave this one standing in here. |
| 00:24:59 | Oh. |
| 00:25:06 | Lydia, this is not the intention. You should stay on that side because that way they have some space too. |
| 00:25:19 | And these chairs we're going to keep them standing like this. |
| 00:25:23 | No, that was already sitting like this. |
| 00:25:24 | Oops! |
| 00:25:30 | Did you shake this already? |
| 00:25:31 | Yes. |
| 00:25:32 | Did you do so very firmly? |
| 00:25:33 | Yes. |
| 00:25:34 | What did you see then? |
| 00:25:36 | Everything mixed up. |
| 00:25:37 | So well blended, then. |
| 00:25:38 | Yes. |
| 00:25:39 | Yes. And after one minute? |
| 00:25:42 | It went back up. |
| 00:25:43 | Then it parted again, didn't it. All right. |
| 00:25:51 | Ah, that is at least some firm shaking you're doing there. |
| 00:25:54 | Yes, we did that too. Except after a while it sort of moves //back up. |
| 00:25:56 | //It goes back up. |
| 00:25:57 | Yes, that 's also a question, isn't it? |
| 00:26:00 | Yes, so this is an emulsion. |
| 00:26:02 | (You already did that twice.) (shake it well) (angled) (Oh, after one minute) (rinse it out) |
| 00:26:14 | Miss? |
| 00:26:15 | Yes? |
| 00:26:16 | (inaudible) when this substance goes up to the top of the test tube, doesn't it have the highest resolution level or something? |
| 00:26:21 | The substance that has the highest resolution is below. |
| 00:26:23 | Oh, then water has the highest resolution level. |
| 00:26:27 | If you're in doubt, you could always look it up in the back of your table booklet, right? |
| 00:26:30 | Yes. |
| 00:26:31 | It foams, miss. |
| 00:26:32 | Yes? |
| 00:26:33 | (inaudible) it's because it's dishwashing detergent. |
| 00:26:35 | Oh, yes, I'll be darned! |
| 00:26:36 | (foams) |
| 00:26:37 | Do you ever wash dishes at home? |
| 00:26:38 | No. |
| 00:26:39 | (inaudible) have a dishwasher. |
| 00:26:40 | That's right, huh, you all have dishwashers at home these days. |
| 00:26:42 | Not me, I have to wash dishes every day. |
| 00:26:44 | Really? |
| 00:26:45 | Yes. |
| 00:26:48 | That's good upbringing. |
| 00:26:49 | (not really) |
| 00:26:51 | We don't have a dishwasher at home either. |
| 00:26:53 | You know what my dad says? As long as we have you guys, we will not need a dishwasher. |
| 00:26:55 | Right. |
| 00:26:56 | My daddy says the same! |
| 00:26:57 | [ laughter ] |
| 00:26:58 | I only have to do dishes when I am late for dinner. |
| 00:27:01 | Yes. |
| 00:27:02 | So, that's //everyday. |
| 00:27:03 | //(inaudible) |
| 00:27:09 | Pink below... pinkish (inaudible) |
| 00:27:17 | (inaudible) (we have a milkshake) |
| 00:27:22 | Did you make a solution? |
| 00:27:24 | Huh? |
| 00:27:25 | Did you make a solution? |
| 00:27:26 | Uh... I did here. |
| 00:27:28 | No. |
| 00:27:29 | Why- |
| 00:27:30 | No, because it's not clear. |
| 00:27:31 | It's not clear, is it? So then it's not a solution. Though it is //mixed together. |
| 00:27:33 | //It is going to sink, just like that one. That one was okay as well. |
| 00:27:35 | It's not a solution. So then what is it? A suspension or an emulsion? |
| 00:27:40 | Uh... a suspension? |
| 00:27:42 | Why? |
| 00:27:43 | Because it doesn't dissolve into each other. |
| 00:27:45 | Yes, but then it could still be an emulsion, couldn't it? What was the difference again between a suspension and an emulsion? |
| 00:27:53 | With one it's a solid substance, and with the other it's a liquid (inaudible). |
| 00:27:57 | Exactly. Look for yourself, it's even written on the blackboard. |
| 00:27:59 | Yes, that's why I know it! |
| 00:28:00 | And so, what have you got? |
| 00:28:03 | Suspension was... oh, yes. |
| 00:28:06 | Yes? |
| 00:28:07 | Yes. We made an emulsion. |
| 00:28:08 | Yes, you've made an emulsion. Therefore, a real milkshake, that's? |
| 00:28:14 | Emulsion. |
| 00:28:15 | Is also an emulsion, right? |
| 00:28:16 | (Miss)? |
| 00:28:17 | Yes? Are you done? Then you can clean up. |
| 00:28:20 | (inaudible) |
| 00:28:21 | Yes? |
| 00:28:22 | (Is this normal)? Look here. |
| 00:28:23 | You may never push it in that deeply, because a little test tube like that breaks easily. The idea is to shut it off, but it is, |
| 00:28:31 | Uh, not meant to be like this. |
| 00:28:33 | Oh. We never learned that. He didn't say it. |
| 00:28:39 | That's just using your common sense a little more. |
| 00:28:42 | (Well, that's kind of difficult). |
| 00:28:43 | Oh well, it didn't break. All right, go ahead and clean up. |
| 00:28:47 | And because you guys were finished this quickly, you can do clean-up duty. |
| 00:28:52 | That gives you enough time to pick up the coats from the floor, arrange them by size, et cetera. |
| 00:28:56 | //(inaudible) |
| 00:28:57 | //Huh? |
| 00:28:58 | (inaudible) (through the room with the coats). |
| 00:29:01 | OWhen you guys are done, you rinse the tubes thoroughly, //and clean everything up. |
| 00:29:03 | //You picked them up from over there? |
| 00:29:04 | Yes, (inaudible). |
| 00:29:08 | Aha. In that case just hang them back //neatly. |
| 00:29:09 | //Miss, the function of (inaudible). |
| 00:29:12 | No, the function of the dish- |
| 00:29:15 | Here, this is the oil. |
| 00:29:17 | We call the whole emulsion, and the dishwashing detergent is what we call the emulsifier. So that is the substance that- what do you have in your hair here? |
| 00:29:26 | It's strange, isn't it? |
| 00:29:27 | Yes, I told you this morning. |
| 00:29:28 | A leaf! //Yes, I was biking through the forest this morning and an acorn hit me in the head which made me ride into a tree. |
| 00:29:29 | //Yes, so- [ laughter ] Yes? |
| 00:29:33 | Yes. |
| 00:29:36 | So the soap is the emulsifier and that's the substance that prevents the two liquids from separating. |
| 00:29:42 | So that's the function of the soap. Making sure that the two liquids don't separate. |
| 00:29:48 | Because here they separated, didn't they? |
| 00:29:50 | Yes. |
| 00:29:51 | Here it's not a mixture anymore. So the soap makes that those two liquids that don't dissolve into each other, that they do not separate. Sandra. |
| 00:30:00 | I have a problem. I can't get the lid on this because of the dishwashing liquid. It keeps popping off. |
| 00:30:04 | Yes? It's well stuck on this way. This is far enough. Just close off, that's the main thing. Then you can start shaking it firmly. |
| 00:30:11 | Okay. |
| 00:30:13 | Turn a little bit, wet it a little bit that might help sometimes, when it's dry it's more difficult, when it's wet it goes smoother. |
| 00:30:19 | (dishwashing detergent underneath) |
| 00:30:22 | Well, now you have to shake harder. |
| 00:30:27 | That's why you shouldn't fill up the test tube too much, then it's harder to shake, you make sure you have a little space left. |
| 00:30:32 | (inaudible). Wait a second, dishwashing detergent underneath. |
| 00:30:36 | Oh, no! Come on! |
| 00:30:41 | That is the dishwashing detergent. |
| 00:30:42 | It's come off again! I did it again! |
| 00:30:45 | Now, what do you see? Yes? |
| 00:30:46 | (dishwashing detergent goes up) |
| 00:30:47 | The emulsifier (inaudible) causes the substances not to separate. |
| 00:30:50 | Correct. Very well. What do you see here? |
| 00:30:54 | Dishwashing detergent. [ laughter ] |
| 00:30:57 | Was that dishwashing detergent red, then? |
| 00:30:58 | No, oh, no that has been, uh, been mixed with water and dishwashing liquid. |
| 00:31:03 | The dishwashing detergent has been added. But what's this here? |
| 00:31:07 | (inaudible) |
| 00:31:08 | It's a pity you have thrown that other tube away, but look behind you for a moment. Do you see those differences? |
| 00:31:16 | A moment ago you saw the difference between the water and the lamp oil very clearly. And now you see that it has been mixed a lot more here. |
| 00:31:24 | This is not clear anymore, this is mixed. So the two liquids are mixed together. So oil and water have been mixed together? |
| 00:31:30 | In the end it will sag a bit again, but not nearly as fast as when you would not add any soap, right? |
| 00:31:36 | Yes. |
| 00:31:39 | So what did we make here? A? A mixture of two liquids that didn't dissolve into each other and what do we call such thing? |
| 00:31:46 | Emulsion. |
| 00:31:47 | An emulsion, well done. |
| 00:31:49 | (inaudible) both substances. So it has a, uh, (I think) a higher density. |
| 00:32:11 | [ laughter ] Yes, what, um, what is the function of the dishwashing detergent? |
| 00:32:16 | My god, you guys started your homework at your own impulse. Very good, very good, you are learning, Jake, you are learning! |
| 00:32:21 | (inaudible) I have finished everything! |
| 00:32:23 | Yes. |
| 00:32:24 | We were supposed to have finished up to 21A, right? |
| 00:32:26 | Yes, that's right. Ha, it 's getting somewhere. |
| 00:32:28 | Yes, um, miss, does question eight apply to the lab or not? |
| 00:32:33 | No, because it doesn't have a gray stripe, does it? |
| 00:32:36 | Yeah, I thought- |
| 00:32:37 | And everything that has a gray stripe is lab, so these are regular questions, right? And you also could have noticed this because, uh, the question has a number, you see? |
| 00:32:45 | (Do we have to do that much)? |
| 00:32:47 | Neat, //huh? |
| 00:32:48 | //Yes. |
| 00:32:50 | We are on duty! |
| 00:32:51 | //Uh, the boiling point of acetone? |
| 00:32:52 | //Yes? |
| 00:32:53 | O(Is this) homework? |
| 00:32:54 | Yes, this is homework. Homework is written on the blackboard, guys, so if you're done then you can continue with homework. |
| 00:33:01 | I already finished that. |
| 00:33:02 | Miss? How can you, uh, an emulsifier is a substance that- how can you, what is the best way to describe that? |
| 00:33:09 | Yes, what is that substance doing? |
| 00:33:10 | Yes, mix with another substance. |
| 00:33:12 | Yes. |
| 00:33:13 | Can I throw this away? |
| 00:33:14 | Hold on for a second, I just want to explain something to him and then you may throw it away. Here that one isn't added, is it? |
| 00:33:20 | No. |
| 00:33:21 | So here I have two liquids that do not dissolve into each other. |
| 00:33:23 | Yes. |
| 00:33:24 | And they have gotten separated again, not mixed anymore we call separated. Here, however, it's still mixed. So what does that soap do? |
| 00:33:33 | And the oil, so that soap causes the oil and the water to stay mixed. |
| 00:33:34 | Mix it with water. |
| 00:33:37 | Yes. |
| 00:33:38 | If I'd want to say this very generally I could say the emulsifier causes two liquids that don't dissolve into each other to stay mixed. |
| 00:33:46 | Yes. |
| 00:33:47 | Yes? Here, Walter, you can clean up now. |
| 00:33:50 | May the glasses come off? |
| 00:33:52 | No, because you're still handling substances. |
| 00:34:03 | Homework is on the blackboard. You can begin with it once you're done. |
| 00:34:10 | //Book and workbook as well? |
| 00:34:11 | O//(We will quickly) clean up the supplies, yes? |
| 00:34:13 | Why don't we have 4.1B? |
| 00:34:17 | Because the introduction about water is so simple, and B are the more complicated sections, therefore they didn't- the section just isn't there. |
| 00:34:25 | So it's not difficult? |
| 00:34:27 | Not section one, no. That wasn't difficult, was it? That was just sort of about what kinds of water there are and all that? |
| 00:34:33 | (inaudible) heat up, heat the water up. That's not that difficult. |
| 00:34:37 | No, now you're talking about lab. I'm talking about the theory in your book. |
| 00:34:40 | Oh, yes. That's not difficult either. |
| 00:34:42 | That was only about what kinds of water there are. Surface water and (heaven) water and so on. |
| 00:34:46 | But you have to study that as well, right? |
| 00:34:47 | Sure, it's something you should know. But it's not so hard in the sense that they should dedicate an extra section to that. Yes? |
| 00:34:57 | Is it going all right over there? Okay. |
| 00:34:59 | (What is this)? They've never had service this good before! |
| 00:35:02 | Really? |
| 00:35:03 | Yes. Ronald took my coat for me. |
| 00:35:14 | Well, this is a slow row here. Everybody is still working. |
| 00:35:18 | (inaudible). Let's see, finish up to 4.2. I have done up to four. |
| 00:35:25 | You've got to (inaudible). (Yes, that is correct). |
| 00:35:29 | Miss, why isn't there a section 4.B? |
| 00:35:31 | That's what he just asked as well. Because that section is so easy, and B is meant for an in-depth section. |
| 00:35:36 | That focuses on the matter a little more deeply, but that's not possible with this subject. |
| 00:35:39 | Oh. |
| 00:35:46 | Gosh, you're taking it for them. What a gentleman! |
| 00:35:49 | (inaudible) otherwise they all have to (inaudible). |
| 00:35:53 | Yes, normally they have to clean everything up. |
| 00:35:54 | Yes- [ laughter ] |
| 00:35:56 | (Yes, usually they have to clean everything). |
| 00:35:58 | They may think that this was planned. |
| 00:36:00 | What's this thing in cola that makes ( ) it bubbles? |
| 00:36:05 | It starts bubbling? |
| 00:36:06 | Well, yes, that it, uh, all that carbon dioxide and all. |
| 00:36:09 | Yes, carbon dioxide is a gas. And that gas gets released so you see that as bubbles. But that is not a question in here, is it? |
| 00:36:19 | No, but when you open a bottle of sparkling water then you see little bubbles everywhere. It seems as though sparkling water is boiling. |
| 00:36:28 | Ah, yes. And what is boiling? You've got to first check up on the definition, right? What's boiling? |
| 00:36:35 | (inaudible) |
| 00:36:37 | That it starts bubbling. |
| 00:36:38 | Now with sparkling water there are bubbles released as well, but is that the same thing? |
| 00:36:41 | No. |
| 00:36:42 | No. What is the difference? Why isn't that boiling? |
| 00:36:46 | (It is also not warm, right?) |
| 00:36:49 | Precisely. What is the boiling point of water? |
| 00:36:52 | Hundred degrees. |
| 00:36:53 | Hundred degrees. Well, normal SPA isn't 100 degrees, so then it must be something different. It's the gasses in there. It's not boiling. |
| 00:36:59 | Okay. |
| 00:37:05 | John, go ahead and start your homework. |
| 00:37:07 | Well, I finished it already. |
| 00:37:08 | You finished it already? Did you correct it already as well? |
| 00:37:11 | No. |
| 00:37:13 | You can do that with those white folders, remember? |
| 00:37:14 | I am working ahead for the time being. |
| 00:37:15 | That's allowed. But then you still have to correct it at home, right? |
| 00:37:17 | Yes. |
| 00:37:18 | What is an emulsifier? |
| 00:37:19 | An emulsifier, in fact the soap you used during the experiment that's the emulsifier, and that causes the two liquids to not dissolve into each other |
| 00:37:29 | Like in this case the water and the oil. |
| 00:37:31 | It's pretty weird. |
| 00:37:33 | Yeah, that's quite a- so it causes them to stay mixed, not dissolved because you still cannot see through the mixture so it's not a solution. |
| 00:37:41 | It only stays mixed if- |
| 00:37:42 | It stays mixed together. |
| 00:37:44 | True, if you wouldn't have the soap in there but with the soap it stayed mixed much longer, even without shaking. At last it sags anyway. |
| 00:37:51 | Soap is not a very good emulsifier, but it stays mixed much longer then it would if I wouldn't have the soap there. |
| 00:37:57 | (inaudible) after one minute (inaudible). |
| 00:37:59 | Yes. |
| 00:38:00 | (soap) |
| 00:38:01 | Miss! (inaudible) |
| 00:38:04 | No, you have to hand your coat over to them. |
| 00:38:06 | Yes. |
| 00:38:08 | Walter! Walter! Don't start wrestling! Take off your coat and hand it in orderly! |
| 00:38:15 | You should throw it over them. |
| 00:38:16 | Yes. (inaudible) Yes. [ laughter ] |
| 00:38:22 | Walter! |
| 00:38:31 | Anything left? Is it all cleared? |
| 00:38:34 | Is everything neat? Okay, come sit down, then. |
| 00:38:41 | Thank you for cleaning up... But do you understand it now? |
| 00:38:45 | Yes. |
| 00:38:46 | It's not a very good emulsifier and if you wait long enough then it will separate. |
| 00:38:50 | But it will stay mixed much longer than when I wouldn't have added the soap. Okay? |
| 00:38:56 | Yes? |
| 00:38:57 | Miss? |
| 00:39:00 | Nah, that- |
| 00:39:01 | But it does look neat this way. |
| 00:39:02 | Yes... but the next time I'll check whether you guys manage to make it just as neat. |
| 00:39:06 | (But we've already been) |
| 00:39:07 | Anyway your turn will come up more than once a year, you see? |
| 00:39:10 | Yes, but there are a lot who haven't been yet. |
| 00:39:11 | //Yes... Yes, what did you want to ask me? |
| 00:39:12 | //(inaudible) |
| 00:39:15 | At question 14, do you put more sugar in tea? |
| 00:39:21 | Yes. |
| 00:39:22 | Yes. |
| 00:39:22 | Yes. |
| 00:39:23 | No, but //(inaudible) |
| 00:39:25 | Yes, but (inaudible) |
| 00:39:28 | No, then you have to stir a little longer. It sometimes just takes time. |
| 00:39:31 | And if it is too cold then, would it still dissolve? |
| 00:39:33 | Yes, but it's more difficult and you can dissolve less in it. You've done an experiment in which you also had cold water with a little bit of sugar. |
| 00:39:39 | And that dissolved all right, only you had to shake a little longer, it sometimes takes more time. |
| 00:39:44 | Oh, right (inaudible). |
| 00:39:45 | Yes, when it gets warmer it's going better, you're right about that. |
| 00:39:58 | Miss, how do you calculate density? |
| 00:40:03 | That part you are going to do with me in the lesson. That homework hasn't been done yet. Now you're working on Chapter 4. |
| 00:40:07 | Homework is up till two point four? //That includes this, doesn't it? |
| 00:40:10 | //Yes, but. Yes, but you understand that it means from the beginning of Chapter 4. |
| 00:40:28 | If you don't know it anymore just go ahead and look it up in your book. It's something you should have learned for today. |
| 00:40:32 | But if you don't know it anymore just look it up in your book. |
| 00:40:37 | Miss? |
| 00:40:38 | All right guys, it's time. We are going to clean up. |
| 00:40:43 | Was there anything you wanted to ask me, Jake? |
| 00:40:44 | How does it feel to be a movie star? |
| 00:40:47 | Well, it didn't feel like that at all. //After a while you forget all about that. |
| 00:40:49 | //Hey miss, with this, two times the amount of water does that boil at exactly the same time? |
| 00:40:55 | No. If I want to get a little bit to boil, does that take longer than when I want to boil a bucket full? |
| 00:41:01 | Oh, so it (inaudible) a little bit like this. |
| 00:41:04 | Yes, exactly, exactly, this is how I do it, yes. |
| 00:41:07 | (inaudible) the other one. |
| 00:41:11 | [ bell ] |
| 00:41:12 | How many times a year are you filmed? |
| 00:41:14 | Never, actually. |
| 00:41:15 | Oh, so this is an exception? |
| 00:41:17 | Yes, that's truly an exception. |
| 00:41:18 | Well, that's a relief. |