Chemical Curiosities: Surprising Science and Dramatic Demonstrations - with Chris BishopJun 05, 2021
Welcome to this lecture on
chemicaldetails. I'm going to start with the liquid from this jug, which I'm going to pour into this cylinder. You can see that it is a nice red color. Let's see what happens if I keep casting. You can see that every time I pour the liquid, I get a different color. In the dictionary, the word specialty... means something remarkable,
surprisingor unexpected. This demonstration seems quite curious at first glance, until we realize that the cylinders were not empty. Each cylinder contained a small amount of a substance that reacted with the liquid... in this jar.
That gave a color change, which we will discuss in more detail later. First we observe the colorless liquids in these two glasses. Let's see what happens when I pour the liquid from this cup... into the other cup. Once again we see a color change; It turns darker and darker blue. But if I keep pouring... it disappears. That's pretty strange. It seems like... it started a
chemicalreaction that produced a color change, but then it changed its mind and went back again. But did that happen? Did that reaction really come back? The chemistry behind these
demonstrationsis based on the simple idea that every substance is...an acid...or a base.
More Interesting Facts About,
chemical curiosities surprising science and dramatic demonstrations with chris bishop...
If it is neither, then if it is in the middle, then we say it is neutral. We can use different substances to see if... something is an acid or a base. The best known is probably litmus. Litmus is a substance that is red in an acid... and blue in a base. However, there are more indicators of this type. The one I used in this experiment was a universal indicator... that can display different colors. It is red in strong acids, in the medium, when it is neutral it is green and in a strong base it is purple.
This experiment was based on an indicator called thymolphthalein which... is colorless in an acid and... turns blue in a base. So the cylinders contained different amounts of acids and bases, which gave the different... colors. In this experiment, the first beaker contained a mixture of thymolphthalein and an acid... and the second beaker contained a base. The idea behind this is that when an acid reacts... with a base, it produces salt and water. They are then a kind of opposites that cancel each other out. When I began to pour the liquid, the acid and thymolphthalein from this glass moved to the base of the other glass.
The base quickly deactivated the acid, causing the thymolphthalein to end up in a base...and therefore turn blue. But as I keep pouring, I keep adding more acid. This neutralizes the base and therefore this liquid also becomes acidic. This caused the thymolphthalein to become colorless again. So this reaction did not go back, but was precisely the same reaction that continued. Now we can ask if there is a chemical reaction that goes backwards. Can chemical reactions really reverse? That's actually a very interesting question. It's a question that... we will return to several times throughout this conference. But first let me show you another example... of a reaction that uses the universal indicator.
This cylinder contains a universal indicator and some sodium hydroxide, which is a base. As a result, it now has a bit of a blue/purple color. I'm going to add some acid now. Now we should see it through a series of colors, similar to these cylinders. The acid I'm using is an acid that will be produced... in water using carbon dioxide. In this glass I have carbon dioxide, but it is frozen. It is now -79 degrees Celsius, making it a solid we call dry ice. When this is heated, it does not melt and become a liquid, but goes directly to a gas.
This way it will always be dry. If I put this dry ice in water, it will react with it and form an acid called carbonic acid. It's the same thing that's in soft drinks. That gives sodas their bubbles. Let's see what happens when I add this. And pay close attention to the color changes. You should see that range of colors. In all of these reactions so far, we mixed two substances... causing a chemical reaction that caused a color change. Now let's look at this bottle. This bottle... contains a colorless substance, but when I shake it... it turns blue.
surprisingbecause it doesn't seem like we are mixing substances. I just shook a liquid. Here's another bottle with the same idea. It's a yellow liquid... that turns red when I shake it. And if I shake it really well, it turns green. There is something more surprising in this. If we keep looking, the green will turn red again. And if we look here, the blue will be colorless again. In fact, the red here will turn yellow again. So it goes back... through that range of colors. I can repeat this. Now if I shake it again, it will turn blue again... and if I shake this one, this one will turn green again.
If I wait, it will come again. So it seems like we have a reaction... that really goes back in time. But the first mystery is actually... why we have an answer. It didn't look like he was mixing substances. What we need to know is that this bottle obviously contains not only water... but also gas. Gas is just air. Air is of course a substance and when I shake the bottle I mix oxygen from the air... with the liquid and that produces the reaction. The next question then is whether this reaction really reversed... when it changed color from blue to colorless.
Unfortunately that is not the case, because what happened... is that a second reaction occurred. This bottle contains a dye called methylene blue. When it reacts with oxygen, it turns from colorless to blue. The bottle also contains some glucose and that ensures that the methylene blue... slowly changes from blue to colorless. This is the same idea, but with indigo carmine. Again we did not have a retrospective answer, but we will continue to search for that answer in this reading. In all the reactions so far we mixed two substances... and then we got a color change. Now let's see what happens when...
I mix these two colorless liquids. First of all, we call this device magnetic stirring device. It spins a small magnet and mixes the liquids that way. I use this... because I don't feel like stirring it by hand. We now have a colorless liquid that is being stirred. Now I'm going to add this second colorless liquid... and then I'll look closely to see if you can see a color change. Keep looking closely. (Audience is surprised) Ok (laughs) Very strange indeed. We mixed these two liquids and it seemed like... no reaction occurred. It stayed there for about 10 seconds and suddenly the substances reacted.
That certainly seems strange and surprising, but what really happened was... there were actually two different reactions... in this cup. The initial response was quite slow. It was a reaction between two substances that together formed iodine. Now remember that this reaction slowly introduced iodine into this liquid. Iodine would normally give a brown color, but you can't see the iodine because... a second reaction with another substance took place in this liquid. That substance reacts very quickly to iodine and absorbs all the iodine immediately as soon as it is produced. So the secret is to ensure that not much of that second substance remains in the liquid.
So the iodine is produced slowly... and is immediately absorbed by the second substance as soon as it is released. If that second substance runs out after about 10 seconds... then the first piece of iodine that forms will remain in the liquid. Because iodine is difficult for people in the back to see, we added a small amount of... starch. The iodine reacts with the starch, giving it that dark blue color that almost looks black. We call this clock reaction. Now that you know how it works, let's look at this experiment. For this, three colorless liquids are used. First I pour this liquid... into this second liquid and then I pour everything into this last liquid.
Now look carefully again. So this is kind of a two-step clock reaction and I'll let you... figure out how it works. In the reactions so far... we have mixed substances and we know that a reaction took place because there was a change... in color. But there are several ways a reaction can take place. One of them is a change of state. The state of a substance... means that something is solid, liquid, or gas. So when something goes from solid to...liquid or from...gas to solid, its state changes. Let me show you an example of a... response where the state changes.
We use these two liquids. I have a red liquid and a colorless one. What I'm going to do is carefully pour the colorless liquid... over the red liquid... creating two layers. What I want to happen is for the colorless liquid... to float on top of the red liquid... in two separate layers. They don't mix, so it turned out fine. What I have now are two liquids on top of each other... and where they touch a reaction occurs. They create a solid... where they touch each other and what I can do is... take out that solid. The moment I take it out of the glass... that allows the two liquids to touch again... and then they react again and produce more solid.
Now, if you carefully... I take this substance out of the cup. Now I lift more of this fabric and that causes the liquids to touch each other again and... form more fabric. The fabric we are making now is nylon. As I speak, we are making nylon... and if I'm careful... I can keep turning and making this long, thin nylon rope... until, of course, we run out of liquids. This is an example of a response... where a state change occurred. Now let's look at another answer where... that happens and for this I need a volunteer. Who would like to volunteer?
If you really want it, come closer. Please give our volunteer a round of applause. If you want to stop here and put these glasses on. What is your name? -Dylan. Okay, Dylan, stay here. Let's do some chemistry. Let's make a solid. I'll start with this bottle... which contains a solution of silver nitrate. I'm going to add a small amount of ammonia...and when I do...you'll see that it produces a brown color. I keep adding ammonia and...very quickly the brown color will disappear. It's completely gone now. Now I'm going to add sodium hydroxide... which will produce a dark brown, almost black liquid.
Now I add ammonia again... and again the liquid will be colorless again. This will take a while. There is. Finally, I'm going to add some glucose. Now that it's in place, I'll put the cap back on the bottle... and put a clip around it. I'm giving it to you now, Dylan, and I'd like you to... shake it really well now. Just shake it well. That's how it works, keep shaking. Now what happens in the bottle is that a reaction occurs...creating a solid...and that substance is silver. Now we make pure silver metal. Keep shaking. It will take about 45 minutes, okay? (The audience laughs).
It actually takes a minute or two...but the harder you shake it, the better it will work. So keep shaking, but don't let it fall. Now we're making silver metal, atom by atom... and you can see it's already starting to turn quite black. That's because very fine silver... is actually black. What we expect to happen is that in about a minute... those silver atoms will stick to the inside of the bottle... and as they slowly become more... we should start to see mirror-like silver metal. ....inside the bottle. You know those Christmas decorations, those shiny balls. They are made with the same chemical reaction.
Those shiny Christmas balls... where the inside has a coating of silver, they are made the same way. It is going well. Can I take a quick look? We're almost there, just a little bit more. It still seems a little dark. Good. Okay, give it back to me. I remove the clip and remove the cap. Rinse. I throw away the remaining chemicals... and rinse the bottle with a little... distilled water. I do it a second time... and a third time. Put the cap back on, let it dry... and put the clip back on. A little more cleaning.
And now if you want to hold him by the neck and if we can get a camera... and look... we have a beautiful silver mirror. I'll take this from you and you can take that mirror home as a souvenir. You can go back to your seat. A quick round of applause for our volunteer. So that was a response that changed the status... and now I want to show you another example... of a response. Once again we go from a liquid to a solid. This bottle contains... a solution of sodium acetate. This sodium acetate is liquid as you can see, but it would very much like to become solid.
It would like to become a crystal, but it needs a little help getting going... and that help comes from small crystals of solid sodium acetate... at this scale. Pay close attention to what happens when I pour the liquid... over the crystals. You see, when the liquid hits the crystals, it immediately turns into a solid. And with a little luck we can make a chemical statue. It seems to work. This is a sodium acetate statue. Although it may seem strange, this is also useful. And this is that use. This is a glove warmer and contains the same liquid as the baby bottle.
So it's also sodium acetate... the one that wants to solidify. But he needs help... and that help is this metal disc. If I do this, if you move the disk back and forth, that's enough to... start the process. And here we see how... it actually changes and as it does, it gets hot. Sogives off heat. Now it's completely turned into crystals and... I can put this in my glove to keep my hands warm... for about half an hour. And I can put this in boiling water... for a few minutes... and the crystals will liquefy again. If I let it cool, it will stay that way...for weeks or months...until I want to use it again.
And I can use it thousands of times. So that was sodium acetate. Now I want to show you another way to make a chemical statue. Chris has prepared this and in this glass... there is a mixture of paranitroacetanilide... and sulfuric acid. Chris has... heated this... and when it is hot enough, it will undergo a reaction in which the liquid turns into a solid. This produces quite a bit of smoke, so we have this cabinet that... sucks in the smoke. (Audience applauds) So that was a reaction that changed the state. Now we have seen reactions involving... color changes and... state changes.
We wonder... if a reaction can go back. You've seen answers where that seemed to be happening, but now that we understand them better, we know they didn't back down. That's why we still want to know if a comment can really go back. To know, we first need to know why the reactions occur. Why does that really happen? To understand this, let's look at some simple chemistry... and that is the combustion of hydrogen. Chris has filled a balloon with hydrogen... and we're going to set it on fire. What's going to happen is that the hydrogen... is going to react with the oxygen in the air... and that's going to produce water vapor... and it's also going to release energy.
This is the reaction between hydrogen... and oxygen in the air. Could everyone who liked this raise their hands? There are quite a few people. And who would like to see a slightly larger version? So that's everyone. The previous balloon made a pop... but this one is going to make a big pop. Since I'm close to that, I use these earplugs. What you can do is cover your ears because it can be quite noisy. The lights can be turned off. And this is the reaction between hydrogen and oxygen. You will have noticed that energy was released. Clearly.
We heard the sound, saw the flame, felt the heat... and probably the front row too. Energy was then released. And what happened... is that the starting materials, hydrogen and oxygen, were in a high energy state. And the reaction has caused them to enter a low energy state. The total amount of energy in the world is always the same, energy cannot be created or destroyed, so the difference in energy was released in the form of an explosion, heat and light. And maybe that's why... reactions happen. So maybe reactions occur because substances go from high energy... to low energy and release the energy difference.
Compare it to a ball that you place on a slope. The ball will roll down, from high energy... to low energy. Maybe that's why the reactions occur. If so, it immediately becomes clear that a comment...cannot go back. That would mean... the ball would roll back up the hill. And that's not going to happen. But for now we will keep this in mind. We will see other reactions that also release energy. We have seen that energy was released in the form of an explosion, light was created in the form of a flame, and... now I want to show you a reaction that produces a particularly large amount of light.
It is the reaction of a rather special element called phosphorus. The word phosphorus comes from Greek and means giver or carrier of light. So it is a reaction that will provide a lot of light. We could leave a little match burning on the table, but we wanted to do it on the largest scale possible. This is the largest bottle on sale in the UK, so you won't find anything bigger than this and... so we're going to burn a lot of white phosphorus... in this bottle. And for it to burn correctly we are going to fill the bottle with pure oxygen.
To do that, we use...liquid oxygen and we're going to do it...using another liquid gas, liquid nitrogen. This vacuum bottle... contains liquid nitrogen. It's colorless and looks a bit like water, but it's incredibly cold. Now it is minus 196 degrees Celsius. Just for fun, I want to show what happens... when we pour liquid nitrogen at -196 degrees Celsius... into almost boiling water. This is what happens. This is of no use, it's just for fun. So this liquid nitrogen is extremely cold and we can use it to... cool gaseous oxygen until it becomes liquid. That's what Chris has done here.
This cylinder contains gaseous oxygen... and Chris passed it through a copper coil... which was placed in liquid nitrogen, which converted the gaseous oxygen... into liquid oxygen. That's in this bottle now. I want to show you something more interesting about liquid oxygen. Now I'm pouring it into... this test tube... and you can see that even though the air... is one-fifth oxygen and the air... is completely transparent... liquid oxygen. It is a beautiful blue color. Now we're going to use this... to fill this bottle with oxygen. I'm going to pour this into the bottle... and we'll add a little more.
This should be enough. The liquid oxygen heats up... when it hits the bottle and evaporates, becoming... gaseous oxygen. As it turns into a gas, it expels the air from the bottle. As you can see, vapors come out of the opening... and the bottle fills with oxygen. And to help a little bit, I'm going to move the bottle a little. You see a small amount of oxygen... of that blue color, sloshing back and forth at the bottom... of this bottle. While this slowly evaporates and fills the bottle with pure... oxygen. Of course, we could also have put a hose from this cylinder... on the bottle and filled it with oxygen that way... but this is more fun to do.
While this evaporates, we add the phosphorus. There are two types of phosphorus. Red phosphorus and white phosphorus. This is white phosphorus, which is the most reactive type. In fact, it's so reactive... that it even reacts with air. If I put it on the table... it would catch fire in a few minutes. That's why we store it in water. Now I'm going to take a piece of white phosphorus and I'm going to put it on a spoon... that is attached to the lid of the bottle. You will see that as soon as the match comes into contact with the air, it starts to smoke... and that will catch fire in a few minutes.
To help you a little... I'm going to heat this glass rod... and touch the match with it. Once the match lights, we'll dim the lights... and what you'll see is the reaction of the match... burning in pure oxygen. You see this beautiful white light. It's a violent reaction... and the bottle fills with phosphorus oxides. That is white phosphorus, the carrier of light. So that was a reaction that released energy... in the form of light. Now I'm going to show you another reaction... in which energy is released in the form of light, but also in the form of sound.
This is a reaction between a colorless gas... contained in this tube, called nitric oxide... and a liquid called carbon disulfide. This is carbon disulfide. I'm going to put a little bit of this in the tube... and then we're going to mix them together. Chris is going to mix the carbon disulfide with the nitrogen oxide. The carbon disulfide evaporates and... becomes a gas. There is a little bit of water in the tube to help them mix better and… once they are well mixed… we turn it on. This reaction happens pretty quickly... so first we'll dim the lights.
Now we've looked at a number of reactions that actually use...combustion and that can generate some very interesting chemistry. Now I'm going to set fire to a new £50 note... as an example of burning. Now first I'm going to dip this bill in a flammable liquid... and then we'll light it. This is my £50 note, it's new and here you can see it burning. The flames have disappeared and fortunately the bill is still... completely intact. I'm very happy with that. The reason the note survived has to do with the liquid. This liquid is made up of 50 percent alcohol, which is flammable, and 50 percent water.
And it was that water... that protected the bill. It absorbed the heat and prevented the bill from catching fire. Frankly, that's not very surprising, because we know that water... is used to put out fires. That's why firefighters also use it. They have hoses... and they use them to put out fires. Now let's look at other ways to put out fires. I have here... three fire extinguishers that use different forms of chemistry. It would be very surprising if we could... use a fire extinguisher not to put out a fire, but to make it worse. And it would be completely amazing if we could use them... to start a fire.
We look at the first fire extinguisher. This is a water extinguisher and it uses water... which is under pressure. When you use the fire extinguisher, water comes out of the hose... you spray it on the fire and it goes out. If I were to use that here, I'd flood this space and then we'll do something else that's similar...chemistry-wise. And for that we use a water gun. This contains water that I can pressurize... and then... Be careful what you wish for. But this looks like that water extinguisher. Spray a stream of water. Could we use this to start a fire?
I would like to have a volunteer for this. You are very fast. Please give our volunteer a round of applause. What is your name? -Ciara. Okay, Ciara, if you put on these... glasses. They are special safety glasses with tinted lenses. That looks great. What you need to do now is spray water...on a metal container. See the tray on that stand? That container contains a mixture of silver nitrate and... and finely ground magnesium. If you can get some water in the tank... we'll see if we can start a fire. Because magnesium is used..., it will produce a very bright light.
That's why I advise you... not to look directly at the container, but to look to the side. Of course you have to look at the tank, because you have to pour water into it and... that's why you have those special glasses. Try to see if you can pour water into the container. Well done! Thank you so much. That was the first fire extinguisher and that was the...water extinguisher. So if you see a fire made of magnesium and silver nitrate... don't put it out with water. The next extinguisher extinguishes with carbon dioxide... and the extinguisher contains liquid carbon dioxide... at high pressure.
I pull out the pin and... if I point the nozzle, we can turn it off. As you can see, the liquid carbon dioxide comes out of the nozzle due to the high pressure... and turns into a gas. Carbon dioxide is often one of the... waste products of combustion. For example, when you burn wood or paper... carbon reacts with oxygen in the air to form carbon dioxide. Therefore, it is a final product of combustion. That's why it also works so well for putting out fires. We use... the carbon dioxide extinguisher to put out a fire. It leaves out the air and, therefore, the oxygen, which is how you put out a fire.
So it would be crazy... to use a fire extinguisher to make a fire worse... instead of putting it out. Let's see what that looks like. We are using concentrated carbon dioxide again... in the form of solid carbon dioxide, also known as dry ice... which we have seen before. This is a block of dry ice. And we are also going to use magnesium again. I've got some magnesium here... and I'm making a little mound... in a slot we made in this block. I'm going to light the magnesium and once... it burns, Chris will put the other half of the block... so that the magnesium is trapped inside.
And if we dim the lights... you can see... the combustion becomes more intense. So this is magnesium burning into carbon dioxide and not putting out the fire...it actually sustains it. It gives off this beautiful white light and the smoke you see is magnesium oxide. This is also used in antacids. I wouldn't recommend using this though. Magnesium reacts with carbon dioxide...creating magnesium carbon oxide. We have a third extinguisher and... that's this powder extinguisher. It contains a pressurized powder... and when we use it, the powder comes out of the hose. We point the hose at the fire to put it out.
They are very good fire extinguishers. If you have a fire extinguisher at home or in your car… it is probably a powder extinguisher. These extinguishers usually contain sodium or potassium carbonate... or sodium or potassium bicarbonate. They are very effective extinguishers...they can be used on many different types of fires...and it would be very surprising if the powder from one of these extinguishers...could make the combustion faster or more intense. But maybe that's possible. This spoon contains one gram of gunpowder. It is composed of three ingredients: Saltpeter, whose chemical name is potassium nitrate and… which acts as a concentrated form of oxygen.
That's why we call it an oxidizer. It also contains carbon. That acts as fuel... and burns due to the oxygen released by the potassium nitrate. Finally, it contains sulfur and that helps combustion and therefore makes the gunpowder burn more easily. What would happen if we made gunpowder and... instead of charcoal, which is the fuel, we put gunpowder from one of the fire extinguishers? That seems pretty strange. We take out the fuel... and replace it with a substance used in fire extinguishers. We are going to use potassium carbonate. If we mix those three substances, then... potassium nitrate, potassium carbonate and sulfur... we get a yellow powder.
This spoon contains one gram of gunpowder... and this spoon contains one gram of yellow powder. Now I'm going to... heat up these two spoons. And we observe if there is any difference between these two powders. This isgunpowder... and this is yellow gunpowder. When gunpowder burns, it does not produce an explosion. It burns with a little smoke, so we don't expect the gunpowder to cause an explosion. Yellow powder, on the other hand, will produce a fairly loud noise. In the next minute... there will be a loud bang that you might want to cover your ears for. As the spoons heat up... the gunpowder will ignite and you will see some smoke.
The yellow dust... is something else. In the spoon the substances begin to melt... now they come together and... the chemical composition changes due to heating. And at some point that mixture of substances... will cause a small explosion. Gives a nice smoke ring. That's part of the
scienceof combustion and that's also how the powder... from a powder extinguisher can make the combustion more intense. As you know, we've been wondering if comments can be returned. I already said it's an interesting question. Let me now show you a fascinating reaction. This glass contains a colorless liquid and... I'm going to add a second colorless liquid.
I also add a yellow liquid to it and... then it turns orange. I add another red liquid and then... it turns green. It looks a little muddy. In about a minute... that mud will disappear and you will be able to see the color. And what I would like... is for you to look closely at the color change. The story behind this answer is interesting. It was discovered around 1951... by a Russian chemist, Boris Belousov. He studied the way citric acid behaves in the human body. He mixed different substances in a beaker and...discovered a very interesting color change and in particular...discovered an oscillating chemical reaction.
That's a reaction that goes through... a series of colors and then back to the first color. You can see that... that muddy thing is leaving. We had a green liquid that now turns blue. So remember that it started out green and now it's blue. Belousov was very enthusiastic about this answer. It seems a little... like the reaction is receding and... a lot of people thought that the reactions didn't do that. He wrote it all down and sent it to... the largest chemical journal in Russia. The editors looked at it and rejected... the report because... they thought it couldn't be done.
Now it has gone from blue to red. So green, blue, red. The report was rejected, so Belousov... sent it to another magazine and they rejected it too, because they also thought the comments weren't supposed to go that way. Something must be wrong, they thought. Belousov was so depressed that he stopped working as a scientist. Subsequently the discovery of him was forgotten. But about ten years later, a chemistry student, Anatol Zhabotinsky, a Russian student, discovered Belousov's notes. Now it has turned blue again. And now it's green again. Remember that order. First green, then blue, then red, then back to blue and now back to green.
Zhabotinsky discovered the notes and... copied the experiment and was then able to publish it at a... conference in Vienna. After this, everyone knew about it and... it became a sensation. People were excited by this kind of response. It's back to blue and now it's changing back to red. Keep... going through those colors. So we seem to have a backlash reaction. Or at least it goes in a circle. Several people began to study these types of responses... and found... other oscillatory responses. Now I want to show you one with a nice story, because this reaction was not discovered by chemists, but by two professors.
Their names are Briggs and Rauscher. They worked at a high school in San Francisco and... used the chemistry classrooms after school. There they discovered another oscillatory response. Again I have a colorless liquid, I add a second and... a third colorless liquid and... then it turns amber. Stay tuned. And here it turns blue. It's a bit like the reaction of the watch. That was the reaction between starch and iodine. But this time it does not remain blue, but becomes colorless. It is colorless, then it turns amber again and if we keep looking it turns blue again. So those are two oscillating reactions.
It seems that we have found reactions that retreat. But that's not what happened. It's not like a ball that rolls down... changes its mind... and goes back up. It's more like a ball... spiraling downward. The color will be... the same color as at the beginning, but it is no longer in the same condition. Some substances have been used. We could continue to observe... these reactions... but after ten to twenty minutes they will stop. This is because all substances are completely used up. So we don't have a... retrospective reaction. Does that mean our theory about reactions... is still good?
Our theory was that reactions are like a ball rolling downhill. It goes from a high energy state to a low energy state and... they release the difference in energy as heat, light, sound or whatever. So let's look at this reaction. This is a reaction between two powders. This cup contains barium hydroxide, it is a white powder. I have a block of wood here and I'm going to put some water on it to make a puddle. I put the cup there. This bottle contains ammonium chloride. I'm going to add that to the barium hydroxide and... I'm going to stir it with this probe that... is connected to this digital thermometer.
You can see that the temperature now is about twenty degrees. Now, if I mix the two substances, we'll see what effect that has... on the temperature. The temperature is dropping rapidly and is now well below ten degrees. The temperature is now negative, so it is already below zero degrees. Now it's minus seven degrees. Then the temperature drops very quickly. Another thing that's happening now is that it went from solid... to liquid. It has turned into a kind of white slush. The temperature is now fifteen degrees below zero, well below the freezing point of water. I put this in a puddle of water... so the water should be frozen now.
Indeed. Now it is frozen in the wood. This is quite strange, because it is a reaction that... does not release energy but actually absorbs it. It absorbed heat from its surroundings and that is why the environment, like the thermometer, dropped in temperature. This is comparable to a ball rolling up a slope. That shouldn't be possible. So this is a strange reaction. It means that our theory of why chemical reactions occur... is not entirely correct or at least not complete. Something is still missing. What is missing from our theory? I'm going to show this using a computer game.
Here we have a hundred disks and... each disk is yellow on one side and... red on the other. The bar on the right... shows how many slices are yellow. Now they are all yellow, but look what happens... when we start the simulation. About a hundred times a second... the computer selects a disk and then decides... whether to keep the yellow disk or turn it over. On the right... you can see how many red and yellow disks there are. We start with just yellow disks... and very quickly we get to a state where about half of them are red and... the other half are yellow.
Let's try again and now we make them all red. They all start red and very quickly... about half are red and the other half are yellow. So we started in a state... that was very orderly. They were all the same color. And as the simulation went on... the disorder increased. It went from a state of order to a more disordered state. This is such an important principle that we have given it a name. We call the degree... of disorder... entropy. Therefore we say that entropy increases as time passes. We started with order and everything became very messy.
The reason why this happens is very simple. There's only one way for the disks... to be all yellow. But there are many ways to make the discs about half yellow and half red. So it all comes down to the number of ways the slices can be arranged... which causes them to go from an ordered state... to a more disordered state. Now you might be thinking that if we wait long enough... that sooner or later, by chance, all the disks will turn yellow again. Then it would have gone from a disordered state to an ordered state. You're absolutely right about that, but you'll have to wait a long time for it.
Now a disk spins one hundred times per second. If we did this a trillion times a second... we'd still have to wait longer than the universe is old... before everyone turned yellow again. Therefore, it is very likely that the world will move from a state of order to a state of disorder. I also have two teenage children and...their bedrooms are the perfect example. If I tidy up your bedroom so everything is tidy and then come back the next day… chances are it has become very messy. And without effort on my part it will not go from disorder to order.
That's the idea of entropy. The entropy will increase and that can explain a reaction. Think for a moment about a solid. In a solid, the atoms or molecules... are arranged in rows. So it's very neat. In a liquid the molecules can move, they are no longer in fixed places. So this is messier than solid state. A gas is even more disordered because its atoms or molecules can move freely. So, as we go from solid to liquid to gas... entropy increases. So there are two things that can cause a reaction. The ball rolls downhill, so the energy decreases.
And there is the increase in entropy, which is why the teenage bedroom effect occurs. This reaction is caused by the increase in entropy. It went from solid to liquid and that increase in entropy is so large... that it overcomes the fact that the energy has to increase for this... reaction to occur. The reaction occurs spontaneously... it draws energy from its surroundings and thus cools it. That is the reason behind this answer. This means that we have two reasons that can explain a reaction. It's not just the ball rolling downhill, but also the bedroom effect. And maybe... now that we better understand what causes the reactions, we can now look for a reaction that backs off.
To find this, I will use the word particularity in a different way. We use it to mean strange, surprising or unexpected, but it can also mean... a desire to learn. Now I am going to tell a story about that wish... of a young chemist, Ira Remsen. As an adult, he became famous for...founding the chemistry department at Johns Hopkins University and...discovering...the first artificial sweetener, saccharin. But when he was a teenager he wanted to know more... about chemistry and that's why he did little experiments. I'm going to tell you a story, in his words, about an experiment he did...when he was a teenager.
The experiment is about the reaction between copper and... nitric acid and once we get to the right point in the story... I'll show you the reaction. The reaction will take place in this bottle. This cylinder above contains nitric acid... and inside the bottle it contains copper. We're using a copper coin and you'll hear why in a moment. We can't use modern one or two cent coins because... they're made of steel with just a thin layer of copper around them. I have an old 1945 penny here and... it's made entirely of copper. We put one of these coins... in the bottle and perform this experiment in a sealed bottle.
All released vapors are conducted through this hose to the sodium hydroxide, where they are absorbed. You will soon see the reason for this. This is the story of Ira Remsen. 'While reading a book on chemistry, I came across the phrase 'nitric acid reacts with copper'. I got tired of reading crazy stuff like this and I was determined... to find out what this meant. I knew what copper was because we had copper pennies. He had also seen a bottle with the word 'nitric acid' written on it... in the doctor's office where he worked at the time. He didn't know the details, but he had a eagerness to learn and an adventurous spirit.
Now that he had nitric acid and copper, all he had to do was learn what... the words "reacts with" meant. So the statement "nitric acid reacts with copper"... would be more than just words. For the sake of learning, I was even willing to sacrifice one of the few copper coins I had. “I put one on the table, opened the bottle of nitric acid… and poured some on the copper… and was ready to see what was going to happen.” Now I'll add the nitric acid to the copper... and we'll see what happens. I think you can see there's a pretty strong reaction going on.
We have a green liquid that bubbles a little and... gives off fumes. I'll continue with the story. 'What was this wonderful thing I observed? The penny had already changed and it was no small change. A bluish-green liquid foamed and smoked on the coin and...on the table. The air in the vicinity of the experiment... turned dark red. A great cloud arose. This was unpleasant and suffocating. How could I stop this? I tried to clean up this disgusting mess by picking it up... and throwing it out the window, which I had opened in the meantime. I learned another fact.
Nitric acid not only reacts with copper, it also reacts... with your fingers. The pain led to another unpremeditated experiment. I wiped my fingers on my pants and discovered another fact. Nitric acid also reacts...with the pants. Looking back now, that was probably the most impressive and...relatively the most expensive...experiment she ever performed. I still say now that... it was a revelation to me. It resulted in a desire on my part... to know more about this type of remarkable action. Simply put, the only way to learn about this was to… see the results, experiment, and… work in a laboratory.” That was the reaction between nitric acid and copper.
It produces this dark brown vapor... and that vapor is what we call nitrogen dioxide. And that's a pretty nasty substance. That's why we also make it in a closed bottle. Nitrogen dioxide is a substance that can teach us more about whether reactions... can reverse. These tubes contain... equal amounts of nitrogen dioxide. What I'm going to do is place one of the tubes in ice water to cool it down. I put the other tube in... hot water, so it warms up. We'll come back to this in a moment to see if anything has changed. Let's look at the chemistry that takes place in the tubes.
Nitrogen dioxide has a molecule... made up of one nitrogen atom and two oxygen atoms. If we have two molecules of nitrogen dioxide, they can react together to form... a molecule called... dinitrogen tetraoxide. In this process energy is released. If that extra nitrogen-nitrogen bond is created, it provides energy. This can be compared to a ball rolling down a hill. The ball rolling down causes the formation of dinitrogen tetraoxide. But that substance... can be divided. The molecule... can split in two to form two more molecules of nitrogen dioxide. And because for every molecule of dinitrogen tetraoxide, we get two molecules of nitrogen dioxide... we have twice as many molecules that can be organized in many more ways... and that means the entropy has increased.
So entropy wants this reaction to go from right to left. So these two effects, the downward rolling ball and... the teenage bedroom effect, cause this reaction to occur in opposite directions. What happens is that the reaction actually goes both ways... at the same time. In this way it achieves... a balance, we call that balance. Both nitrogen dioxide and... dinitrogen tetraoxide are present. The relative amounts of these depend on temperature. If we increase the temperature, if we add energy, comparable to pushing the ball up the mountain... then we go from right to left. If we let it cool, we will move it from left to right.
That's the prediction... and we can test it... because nitrogen dioxide is dark brown, as you can see on the bottle... but... dinitrogen tetroxide is colorless. If we go back to the tubes and this is the tube in the cold water, you'll see that it has turned a pale color. This is the hot water tube and if I put them next to each other... you will see that when you heat the gas you get a dark color and... then it contains more nitrogen dioxide. As it cools... it has made it paler and contains... more dinitrogen tetraoxide. And to test our theory... we take the dark, warm tube... and place it in cold water.
We place the pale, cold tube in the warm water. We'll come back to this in a moment to see if the colors have been changed. That brings us to the end of this lecture, but I'd like to show you... another feature that uses an interesting and special element. This element was found in a mine... on the outskirts of a small town called Ytterby, near Stockholm, Sweden. There they extracted minerals from the ground and... they found a mineral that was quite strange. They didn't understand... what was in that mineral. In the end, they felt there was a new element to it.
This was at the beginning of the 18th century. At that time it was normal that if you found a new element you could also determine the name. It was decided to name the element... after the city, so this element is called yttrium. What is interesting is that this mineral did not contain any new elements, but was found to contain four elements. That is why it was decided to name all the elements after the city of Ytterby. That's why these four elements are called... yttrium, ytterbium... erbium and terbium. Which can be a little confusing. Let's look at the first element, yttrium.
Yttrium can be used to make a mixture and I have some of that mixture here. It's called yttrium barium copper oxide... and it's actually a hard, black ceramic material. What I'm going to do is put this in...liquid hydrogen. And now that yttrium-barium-copper oxide is cooled to minus 196 degrees. That's going to take a while, so while we wait, I have a little more of that stuff in this glass, exactly the same as the first one, and I'm going to cover it with...liquid hydrogen. So that's cooling now too. At room temperature this material is not very special, but when it is cold enough it acquires a very special property.
It then becomes a superconductor. A superconductor is a material that has lost all of its electrical resistance. A material that no longer has electrical resistance has the property of repelling a magnetic field. This ring is made of steel and has small... but very strong magnets that point alternately upwards with the north and south poles. Once it has cooled enough, we will see if yttrium-barium-copper oxide can repel the magnetic field of these magnets. This takes a while to cool down. When I look at this, I see that it is boiling quite strongly. This means that the ceramic material gives up its heat... to the liquid hydrogen, evaporates it, so to speak, and therefore cools.
Now I'm waiting for it to stop boiling and... when it stops, the ceramic material... has reached the same temperature as liquid hydrogen, i.e. -196 degrees. If I take it out now, we'll see if this can repel a magnetic field... This is actually a pretty special type of superconductor; We call them type II superconductors, which means they can repel and retain magnetic fields. We also put one in this cup and... underneath there is a cylinder and above it... a very strong magnet. The field from that magnet already passed through... the ceramic material before I added the liquid hydrogen.
It has now cooled and should have become a superconductor... and hopefully captured the magnetic field. So it should still contain that... field. You should then be able to remove this bracket from under the cylinder. By the way, the cylinder bears the logo of the International Year... of Chemistry. 2011 was the year around the world that we celebrated the joy of chemistry... and its importance in our daily lives. I thought it was a good way to draw attention to that. This has already cooled down, so I'm going to see if I can carefully lower it down. Thank you!
This actually brings us to the end of the conference. Before we head home, I think it would be nice to stop with a... fun experiment. But before I do that, I would like to ask you to thank someone who has helped me a lot... in preparing and presenting this conference... and that is Chris Brackstone. Before stopping, we took a quick look at this block of dry ice. You may remember that we burned magnesium in this. The chemistry was that magnesium reacted with carbon dioxide to form...magnesium carbon oxide. If we look at the surface... we see that it is covered with a white layer and that is... magnesium oxide.
If we dig a little... we see this black material and that's carbon. And, of course, we had changed both tubes. We place the darker one in cold water and the lighter one in warm water. And we can see that they have indeed changed color. So the dark tube has cooled and turned light... and the lighter tube has warmed and turned dark. So we come to the extraordinary conclusion that reactions can move forward... and backward at the same time. That's really... the end of the conference. But we have one more experiment to finish with. We are repeating one of the experiments we have done before.
It's the experiment... with nitric oxide and carbon disulfide... but on a larger scale. Chris brings the tube of... nitrous oxide. I add the carbon disulfide. Chris now mixes the two. Once they are well mixed we turn it on. We dimmed the lights for this and... thank you all so much for coming.
If you have any copyright issue, please Contact