By Antonio Torrisi
Friday, 1st July 2011.
The first rows of the lecture theatre were full of smiling faces and eyes full of expectations. “Guys, I don’t know you but I’m in the mood for something sweet”
Dave pointed to the audience.“Do you like ice-cream?”
A wave of sound with mixed frequencies fully invested me with all its intensity:
”Yeaaaaaaahhhhhh!!”. The kids had just gone mad. “Ok, what sauce do you fancy?”
Dave continued, “Cream? (“Yeaaahhh!!!!”), Chocolate? (“Yeaaahhh!!!”), Raspberry? (“Nooooooo!!”); “No Raspberries? But I like them…” (“Nooooooo!!!”)”
But there was a problem: there were sauces and raspberries, but there was no freezer.
It was then that Dave came out with a brilliant idea: “I know what we could use: the liquid nitrogen!!”.
A look of scepticism was written across the childrens’ faces. But a few minutes after the smoke in the room had started to dissipate, we could see their eyes twinkling: there was a great vanilla and chocolate ice-cream for at least fifty people.
Dave had got them this time again.
It was the end of the last session of SAUCE 2011 (Schools at University for Climate and Energy) event at the London Metropolitan University (LMU), organised by the Department of Applied Social Sciences (DASS), part of an EU project in collaboration with other European universities in Latvia, Germany, Austria, Netherlands and Denmark. The event consisted of a series of activities, such as talks, demonstrations, films and practical activities to introduce and inspire children from schools in London about issues such as energy, environment and climate change. The EU project covered two years from 2009 to 2011 and this year it ran from the 20th of June to 1st of July 2011, involving a total of 700 pupils from schools in Islington and Hackney.
Nicholas Watt, a lecturer in sociology and social policy at LMU, opened the session by talking about the difference between climate and weather, illustrating the advantages and disadvantages of possible renewable energy sources and speaking about eco-sustainability. After about ten minutes his voice announced: “But now it is time for some science demonstrations, which will be given by David and Antonio, two scientists from University College London”.
It was our turn to come onto the stage: Dave and I gave demonstrations about states of mattes and presented one of the main protagonists of climate change issues on Earth: carbon dioxide (CO2).
Dave started with simple question:
“Hey Guys, what do you think is in the containers?”, he asked, pointing at two big, glassy beakers, full of two transparent liquids.
“Water!” was the answer in chorus.
“In both of them? Are you sure?”, Dave enquired.
“You’re right!”, Dave agreed. ”In fact in one there is water and in the other toluene.” He continued: “So more generally speaking, what can you see in the two recipients?”
“Liquids!” was the right answer from the audience.
This was our chance to speak about the different states of matter: solids, liquids, gases, their properties such as volume and density, gas expansion. The kids rightly identified temperature as the fundamental factor which allows a substance to move from one state to another. They also learnt about sublimation, the direct transition from a solid state to gas, without passing through the liquid state as temperature increases.
The protagonist was already on the stage: dry ice, or solid CO2, which it is at temperatures below -78 Celsius.
CO2 is a nasty gas for the environment. Scientists discovered that there is a strong correlation between the amount of CO2 in the atmosphere and the temperature of the planet Earth. How does this happen? CO2 is denser than air and once in the atmosphere it does not leave it, but it stays there covering the planet like a blanket, which keeps the warmth of the planet coming from sunlight reflection. Bubbles can demonstrate this. Typical bubbles are made of soap and air. If we look at their behaviour we can see that when we blow them around in the atmosphere they fall down onto the ground, because they are denser than air. Let us blow them out into a box, where we previously put some dry ice, which sublimated. The bubbles float for a while! This is because there is CO2 gas in the box which is denser than the bubbles! Then they eventually fall down to the bottom, because CO2 tends to penetrate into the bubbles.
CO2 is nasty also for another reason. When in contact with water it gives reaction by forming acids that’s why Coca Cola, Fanta and sparkling water are all acidic. The same reaction occurs in the oceans when they adsorb CO2 from the atmosphere. To demonstrate this we put just tap water in a large glass container and used a pH indicator — this is an organic substance, which is highly sensitive to the acidity of a solution. It changes colour towards yellow when acidity increases. We put some drops of the substance into the water and the colour turned purple in few seconds. Then we dropped some dry ice pellets into the water. The guys got excited: the mixture stated to bubble and smoke violently.
But the best was still up to come…within a minute or two the colour of the solution turned rapidly from purple to yellow — and the children all started clapping loudly! Sweet! Of course, with humans, the increase in acidity caused by drinking sparkling water is only moderate and not harmful, but other beings on Earth are more sensitive to small variation of acidity, such as corals for example.
“Dry-ice is cold, below -78 Celsius, but we can get even colder! We can go below -195 Celsius!”, said Dave, introducing the pupils to liquid nitrogen.
Liquid nitrogen evaporates immediately in contact with any object at room temperature. We tried to pour it in a normal glass and it disappeared in the air within less than five seconds. You need a special kind of flask to keep it at -195 Celsius: the Dewar flask, which is the precursor of the thermos flask.
We showed the audience the thermal shock effect of liquid nitrogen on objects like rubber or bananas when kept in it for a few seconds and Dave invited volunteer teachers to put their fingers in the liquid nitrogen, to the excitement and fascination of all the pupils. Teachers are brave: we had two volunteers! The secret is to keep the finger in for just a fraction of a second.
What is liquid nitrogen useful for? Refrigeration, food conservation, helping high-temperature superconductors reach their lower operative temperatures, cooling computers, improving the quality of spectroscopic signals and freezing processes, like those involved in making ice-cream…
SAUCE 2011 ended with a blast of enthusiasm and although I am not sure it hit the target of inspiring the kids on topics such as climate change, it definitely gave a boost to their curiosity towards science in general. The kids were enthusiastic and left the room with chocolate-sauce-covered smiles on their faces. We left with a lot of new learning about children: they are responsive, prepared, merciless, and they hate raspberries. I later found out that raspberries contain antioxidants, vitamin C, iron — in other words they are healthy. It was then that I realised why children don’t like them.
The official website of SAUCE project is: http://www.schools-at-university.eu/index.html