The Magic of Chemistry - with Andrew Szydlo

Yes, when I was 10 I lived in Shepherd's Bush in west London, not far from here. And every Saturday afternoon she used to go to Shepherd's Bush market. You see, she really wanted to see what people were selling. What they were buying. But most importantly, what they were throwing away. Because very often among the rubbish I could find something useful For example wooden boxes, with which I could make a cricket bat But, every Saturday afternoon There was a very strange man He was completely daring and he sold medicines He sold medicines in the form of purple tablets Like this, and he told everyone That these tablets were very good for you Because they could cure you of any illness Whether you had a headache, a toothache, muscle pain, neuralgia, homesickness, whatever, this medicine would cure he.

So people were very fascinated to be able to buy this medicine. It was made about three hundred years ago. They quickly realized that there are 2 main gases in the air, one of them responsible for combustion and which was called Oxygen. They called the other Nitrogen. And they recognized that approximately one fifth of the air is Oxygen. And then they began to do experiments to make fuels burn better, not by mixing them with air but by trying to mix them with Oxygen or get them to combine with Oxygen and I wanted to show you the result of one of those experiments that was a notable triumph of science. of

chemistry

and was produced using the most mundane substance you can imagine: cotton.

Cotton is a natural fiber. Human beings have known it for more than five thousand years and we know that cotton was cultivated and used for the first time on a large scale in India and also in Mexico. But it is in India that the great cotton culture, the culture of cotton weaving, cotton weaving, grew for thousands of years long before reaching Europe. Now cotton, what is cotton chemically speaking? Well, it is a very delicate fabric, it is used in clothing of course as you know and for cosmetic applications. and chemically speaking it is called cellulose. It is a naturally produced polymer that is very, very comfortable to the touch and warm to the touch. and that is why it has a great place in our human history.

Not to mention the fact that cotton played a huge role in the industrial revolution in this country during the 18th century, when cotton weaving and spinning were developed. Now, if you look closely, who would think of getting burned? Well, the chemist thought about burning everything and this is one of the things. They burned cotton, you see, they thought it could be wonderful. There it is, burning in the air, an enormously boring experiment. It is seen to burn in air, because air contains only about 20 percent oxygen. This is what we have incomplete combustion. It burns with this kind of slightly yellowish color. calls and a little bit of ash remains and it is nothing spectacular, almost like a piece of paper.

Now what I wanted to tell you next during the 19th century, in the middle of the 19th century, chemists were experimenting with adding oxygen to different fuels, either by mixing them or combining them chemically and the remarkable result was achieved by 2 scientists who worked independently. cotton, one of them was Ascanio Sobrero who was Italian. The other was Christian Schönbein, a German organic chemist. Christian Schönbein was a good friend and colleague of the great Michael Faraday, who gave teaching lectures in this very place for more than 30 years during the 19th century. So it was Christian Schönbein who was the first person who managed to add extra oxygen to cotton.

Now, how did he achieve that? And also, I told you at the beginning that we can often recognize a chemical change by a color change and yet you say look at this cotton I have here, it looks the same and feels exactly the same as the cotton I have. I had a minute ago. And yet, this has additional oxygen, as I'll show you in a second. How is this different then? Dear children, the difference can be seen by weighing it. You'll see, if you weigh one of those. They weigh 1.7 g but this one weighs 2.8 g. An extra 1.1g of Oxygen.

That's a lot of extra oxygen added. It actually has some nitrogen too. Can you say how did they add this? Well, first of all let's see if it works, of course, because there's no point in talking about the effect if we don't see how it was done if it doesn't work. First of all, let's find something to talk about. So here is our cotton with extra oxygen added. And let's see how this burns and see the difference. And as you can see, there was an instant combustion. Everything burned very, very, very quickly and there was practically nothing left at all, as you can see.

Now that, of course, Now that's clear, dear children, it is proof that the experiment was successful. Now, when Schönbein accomplished this experiment, he was absolutely delighted. And as Sobrero said, they were working separately, one of them with cotton, the other with glycerin and They were similar substances and they achieved this type of result. They thought this was absolutely amazing. FYI, the way it was made is using a substance very similar to that used in gunpowder. Gunpowder contains sulfur, carbon and potassium. Nitrate, nitrates. This uses nitric acid and sulfuric acid. You mix them and soak the cotton for half an hour.

And you end with this. So oxygen arises indirectly. But then chemists are people who understood this process. and that is why they can cause the effect. Now, what I've really done here is a high explosive. Of course, it is a very, very dangerous substance. Is popular. Its name in the industry is called gun cotton, nitrocellulose. It is enormously dangerous. It is used in engineering and for military purposes. And I would like to demonstrate to you an explosion. Unfortunately, that would be too dangerous. So what I'm going to do is demonstrate a propulsion and even 2 propulsions if we're lucky.

And what is a propulsion? A propulsion is a directed explosion. An explosion is a rapid release of gases everywhere, breaking something apart. However, a propulsion is when you direct them in a direction. So I'm going to start by showing you how to use this to make a simple mortar. It's quite similar to a canon. And I'm going to propel a ping pong ball, hopefully onto the roof of our beloved Royal Institution. Now what I have here is a special, it's like a canon. Technically it is called a mortar and its principle is that the fuel that will be gun cotton burns at the bottom.

Release a large amount of hot gases and they will force the ping pong ball to fly, hopefully to the ceiling. So that's the beginning of this and what I wanted to tell you, dear children, is that every time you see one of those fireworks shows where there are huge projectiles exploding in the sky and colors. All of them are projected from these. Only they are made of thick cardboard and their shelves rise and explode in the air. We're not going to blow up the shelves up there today. We're just going to shoot ping pong balls. Now