A Christmas of Colorful Discovery for Kids

How does evaporation work?

Good morning, children. I’m Peter, and I work on evaporation instruments. And as it’s very cold this morning, I have made some hot chocolate, which is the perfect way to introduce you to evaporation.

You see all that swirling steam coming from the cups? Well, as the hot chocolate heats up, it begins to jump about and won't stay in one place, and the droplets near the top of the cup sometimes pop out because of all the jiggling. And once they pop out, they hit the cold air, lose energy, and stop jiggling. This is why the steam disappears after a while in the cold air.

If you hold your hands above your cups, you will feel them getting a little bit wet. This is you catching all the droplets that jiggled and popped out of the cup. But look at your hands, they have clear liquid on them, not chocolaty water! This is because it takes different amounts of heat to make things jiggle – this is called the boiling point.

In hot chocolate, the water is the first thing to start jiggling, so it pops out first. If we continued to heat the hot chocolate long enough, all the water would pop out, and you would be left with just the chocolate.

We have a special machine in our lab that can do this. But our machine has a special trick. Our machine can make the water pop out much faster. Come and see.

By putting hot chocolate in our special round flask, we can suck out some of the air surrounding the hot chocolate. This creates what we call a vacuum. When there’s less air around the hot chocolate, it doesn’t need to jiggle as much to pop out. That’s because, in a vacuum, there’s less air pressure pushing down on the liquid. Normally, air pressure holds the jiggling molecules in the liquid, but in a vacuum, it’s easier for them to escape.

So, in our machine, the water in the hot chocolate can start jiggling and popping out even when it’s not as hot as in your cups. The boiling point has been reduced – it’s like giving the water molecules a little extra help to escape! We can even catch the water in a separate part of the machine, leaving behind the yummy parts of the hot chocolate.

So now we know all about how to turn water into steam. Who can tell me what happens when we heat up ice like we heated the hot chocolate? “It melts,” says one of the children. “It turns into water,” says another. That’s correct, but what if I told you we also had another machine that could turn ice into air without melting into water?

Come and meet Bruno, who will tell you how it works.

How does freeze drying work?

Hello, children. I’m Bruno, and I work with freeze-drying machines that are used to make food for astronauts to eat in space. How do people get to space? “In a rocket,” says one of the children. Exactly, and it's much easier to send a light rocket into space, just as it’s easier to throw a small pebble than a huge rock.

Because there are no shops in space, the astronauts must take all their food with them, and food can be very heavy, especially if you need enough food for months. So, to make things lighter, we use our special freeze drying machine.

First, we take whatever yummy food the astronauts might want to eat, such as strawberries or ice cream, and we freeze it until it's super cold and solid.

You remember how the hot chocolate jiggled as it got hot; well, as you make things really cold, all the jiggling stops. That is why ice is solid and doesn’t fall about all over the place like water.

If you try to remove the water from ice cream in the same way you removed the water from hot chocolate - by heating it up - the ice cream would melt and turn into liquid, losing its shape; it would become thick and creamy before it finally boiled and let the water out.

Or, with a strawberry, you could squish it to get the water out, but you’d end up with a squished strawberry.

The magic trick of the freeze drying machine is that it can turn the ice into steam without turning into liquid first. So, you can take the water out of the ice cream without melting it – or take the water out of a strawberry without squishing it.

This works by a trick called ‘sublimation’ that turns ice into gas, bypassing the liquid stage. It’s like if you were playing a board game and you got to skip ahead several spaces.

When we freeze dry food, we freeze it until it is solid, and we place it into the freeze-drying machine, where something cool happens. We lower the air pressure, like Peter did with the rotary evaporator. This removes some of the air, creating a vacuum, and makes the inside of the machine a bit like space!

Now, when we heat up the food, the water instantly jiggles free as a gas because there is not enough pressure to hold it in the sample. This water vapor gets removed from the machine, leaving behind the dried food.

Here, try some freeze-dried ice cream. Notice how it still has the same shape but a more intense flavor. It is also much lighter as we zapped out all the water. It is also not cold, yet it hasn’t melted. This food can now be stored for a long time without needing a fridge, and when astronauts add water to it, it becomes like normal food again!

So, now you have seen how to jiggle water out of hot chocolate and zap water out of ice cream. And we have one more magical machine that Padma will show you. This machine can do more than just remove water – it can pull something apart and separate it so you can see all the parts that made it.

How does chromatography work?

Hello, children. My name is Padma, and I’m here to show you our special machine for separating things.

Imagine you are on the beach searching for seashells, but all of the shells are hidden in the sand. One way to find them would be to use a big sieve, like the type you use when cooking to sift through flour. If you put a big pile of sand into the sieve and shake it, all the sand passes through the little holes, and all that remains is the shells!

But what if you wanted to separate the shells? You could do this by creating sieves with different size holes – small holes, medium holes, and big holes. Now, you can easily separate the shells according to size.

But what if you want to separate different types of shells that are the same size? Well, you could then create sieves with different-shaped holes – round holes for round shells or long holes for thin shells.

There are many clever tricks you can use when you want to separate things, and that is what we do with these chromatography machines.

In these machines, there are two important things. One is what we call the stationary phase. This is like the sieves we used to find things in the sand. The sieves are not stationary as we must shake them to make the sand pass through, but they would be stationary if we had a way to blast the sand through – like having a big fan that blew the sand through.

In the chromatography machine, we blast our mixture using a mobile phase. The mobile phase is like the wind or a stream of water that helps carry things along through the stationary phase.

In our machine, the stationary phase is like a special type of sieve. It doesn’t have holes, but it does have a surface that interacts with different parts of the mixture in different ways. Some parts will stick to it a lot, and some just a little.

Now imagine a mixture of different colored dyes. When we pour this mixture into the machine, the mobile phase, which can be a special liquid or a gas, blasts the mixture through the stationary phase. The different dyes will stick to the special sieve in different ways, and they will move at different speeds.

The dyes that don’t stick much will move faster and come out first. The ones that stick a lot will move slowly and come out later. So, by the time everything comes out the other end, they have been separated.

Look at this strip of paper with different colored bands on it. This is the result of a simple chromatography experiment. Each band of color was once mixed with the others, but now they are separated, just like shells of different sizes and shapes.

And that is the magic of chromatography. It helps us separate things that are mixed together, even if they are very, very tiny or seem very similar. It’s a bit like being a detective, finding clues to solve a mystery, except we use this amazing machine and science to help us!

You can even perform a simple experiment at home using different color pens and coffee filters.

We hope you enjoyed this introduction to Evaporation, Freeze-Drying, and Chromatography. In the coming months, we hope to go into detail about these essential techniques and reveal all the remarkable things they help achieve.

Thanks for joining us on our Colorful Journey!