Meet CO2


Carbon Dioxide gas can be detected by the human nose.


A small empty box, bigger than your fist.

A piece of paper to cover the box

Dry ice

a working nose.


Places dry ice into the box and cover the top of the box with a piece of paper.

(Warning be careful with dry ice, if your skin contacts dry ice for more than a few second you may get a painful frostbite. Wear gloves when handling dry ice.)

Wait 5 minutes.

To Do and Notice

Slide the paper off the top of the box so as to not disturb the gas inside.

Stick your nose and tongue into the box and take a gentle whiff of the gas. Or fan some of the gas toward your nose with your hand. Pretend you are scooping the gas out of the box toward your nose.

Notice the tangy smell and taste of the carbon dioxide.

What does it remind you of?

If you lower a burning candle into the CO2 the candle will go out. The candle requires oxygen to burn, it cannot burn in carbon dioxide.

What's Going On?

The dry ice sublimes at room temperature, it goes directly from being a solid to a gas.

The carbon dioxide gas fills the box. the carbon dioxide gas drives the atmospheric gasses up and out of the box. Carbon dioxide has an atomic mass of 44 grams per mole while the atmospheric gasses have an average mass of 29 grams per mole so the denser carbon dioxide drives the less dense atmosphere up and out of the box.

You probably smelled the smell of soda water. Soda water is water with carbon dioxide dissolved in it.

When it enters water in the mucous lining of your nose, or water in the saliva in your mouth, carbon dioxide produces carbonic acid. The acid produces the tangy taste of carbonated water.

Carbonic acid is H2CO3 which dissociates in water to form both

HCO3- and H+


CO3-- and 2 H+

The release of the hydrogens identifies it as an acid.

So What?

Tapwater often has a pH of 5.6 due to dissolved carbon dioxide.

Rainwater unpolluted by other acids has a pH near 6.0.

Acid rain contains other acids which lower the pH still further.


Joseph Priestly, the discoverer of Oxygen also discovered that CO2 will dissolve in water to produce the tangy drink known as soda water. He received a medal for this discovery.


Scientific Explorations with Paul Doherty

© 2006

22 April 2006