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.

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