As you may know, I have recently helped to organise an open day demonstration at my University and I thought I would take this opportunity to show you what the end result was.
Carbon dioxide comprises of two oxygen atoms bound to a carbon atom. It is colourless, odorless, non-flammable, and slightly acidic. For most of these experiments I used solid carbon dioxide or dry ice. Carbon dioxide only exists as a solid and gas at atmospheric pressure and therefore sublimes between the two states. Dry ice sublimates at −78.5 °C (−109.3 °F) at atmospheric pressure and this extreme cold makes the solid dangerous to handle without protection due to burns caused by freezing. I don’t recommend playing with with dry ice. Please do not repeat any of these experiments at home. These were carried out by trained professionals wearing the correct PPE.
Carbon Dioxide is acidic
Carbon dioxide is acidic in solution. When it is dissolved in water it forms a weak acid called carbonic acid. To prove this, solid carbon dioxide (dry ice/cardice) was added to a solution of amine, in this case monoethanolamine, containing universal indicator. Universal indicator is purple/blue for alkalis and is red/orange for acids. You can clearly see that, on addition of the dry ice, we get a colour change from purple to blue to green to yellow to orange. Pretty cool huh?
Carbon dioxide is more dense than air
As you may know, the density of carbon dioxide is around 1.98 kg/m3 which is about 1.5 times that of air. To demonstrate this, we blew up a balloon (you can fill it with nitrogen also) and placed this on a layer of dry ice, which was subliming to give us CO2 gas. The balloon rested nicely on the layer of CO2 glass and gave us the illusion of a levitating balloon. We also showed this by blowing bubbles onto the CO2 but I forgot to take photos of that. The bubbles bob up and down on the layer of CO2 gas. It is pretty neat and well worth seeing for yourselves.
Some people asked the question, “but don’t we see balloons floating all the time when they are filled with helium?”…this of course is the opposite phenomenon, where helium is less dense than air.
Expansion of carbon dioxide from solid to gas
Dry ice and liquid carbon dioxide (which can be formed under pressure) expand they becomes a gas. Simply put, 44g (1 mole) of liquid CO2 will give approx. 22.4 litres of gaseous CO2. We demonstrated this expansion by filling a nitrile glove with dry ice and heating this up with water. We tied up the glove with a cable tie and watched it expand…behind a blast shield, just in case.
The glove got around 5-6 times this size. This experiment was very much a crowd pleaser and I am pleased to say that the glove didn’t once explode.
Carbon dioxide as a fire extinguisher
You will often have come across carbon dioxide fire extinguishers which are often used to put out electrical fires. The fire extinguisher basically works by replacing any oxygen, which is required for a fire, with carbon dioxide.
For this experiment you can use dry ice but you can also use carbonated drinks such as Coke or lemonade. As you can see, you put a CO2 source in a conical flask and seal it. You then attach a tube which allows CO2 to escape and you point the end of this tube at the ‘fire’. In this case we used a tea light but we also demonstrated that six birthday candles could be blown out.
Capture of carbon dioxide with monoethanolamine (MEA)
Carbon dioxide is a major greenhouse gas, responsible for substantial amount of global warming, currently ca. 380ppm. Post-combustion carbon capture removes CO2 from power station flue gas streams and can potentially be fitted to existing power stations. The process utilises amine solvents such as MEA, which reacts with CO2 to form a carbamate (shown below) or bicarbonate salt, and this holds it in an aqueous solution allowing other unreactive gases (N2, O2) to pass through. On heating to around120 ºC, the carboxylated amine regenerates the CO2 as a gas stream, and the amine solution is recycled.
In this experiment we added a solution of MEA to a pre-filled bottle of gaseous carbon dioxide. This creates a vacuum when the amine ‘captures’ the CO2 and crushes the bottle from the inside. This process is exothermic (gives out heat) and so the bottle gets very warm. Conversely, the release of CO2 is endothermic.
After CO2 capture to give carboxylated MEA, we then showed that CO2 release is possible. As previously mentioned this is usually carried out by simply heating the carboxylated amine solution. In this case, however, we used acid to release the amine and thus the CO2 gas. The carboxylated MEA was removed from the crushed bottle and poured in to a conical flask and acid added. The released CO2 was seen as bubbles which could also successfully blow up a balloon.
I hope you have enjoyed reading about my open day demonstration. Any ideas you have on future experiments to show off would be great and any comments on those shown above would be grand.