The Many Forms of Carbon Dioxide
What have I demonstrated in class and what have we learned?
The air around us contains CO2 in the gas phase.
Dry Ice is solid carbon dioxide, and is approx. -78.3 oC That’s VERY cold.
Sublimation is the phase change from solid to gas, which happens at room temperature ( 20oC) and pressure ( 1 atm). Sublimation requires the input of heat energy; this heat comes from the surrounding warm(er) air or water.
In water, a chunk of dry ice sublimes and gives off lots of bubbles of CO2 and makes lots of white vapor that crawls out of the beaker and goes over the counter and “sinks” towards the floor.
This is because the CO2 molecules are too dense to rise; each molecule of carbon dioxide has more mass than the nitrogen molecules (N2) which are the main components in air (78%) .
The chemical reaction of carbon dioxide in water yields Carbonic Acid:
H2O(water) + CO2 à H2CO3
We know it forms an acid because we used an indicator (bromothymol blue) that changes color(from blue to yellow) in acidic solutions.
Carbon dioxide can be a clear liquid if it is pressurized to 5.1 atm or more. We saw this in the apparatus with the clear hose and the pressure gauge. We put some crushed up dry ice in the hose, closed the valve, and let the vapor form (it sublimed) and cause the pressure to develop. Suddenly the white pieces of solid carbon dioxide turned to a clear runny liquid (looked like water), when the pressure was near 5 atm.
