Dry ice is the solid
form of carbon dioxide gas. It is an interesting substance in that it sublimes, or changes directly from the solid
to the gas
phase. Since the liquid
state is bypassed, dry ice does not melt. The solid
magically seems to disappear as it changes to CO2(g)
Carbon dioxide is a very common substance. It is a byproduct of animal respiration. You exhale the very same type of molecules that are in dry ice! Carbon dioxide is more dense than air. Some fire extinguishers make use of the fact that as the CO2
falls and surrounds a flame, the flame is smothered. The dense carbon dioxide gas
pushes away the air (which contains O2
needed to support combustion). Another use for CO2
is in the production of carbonated soda. The gas
is bubbled through cold cola syrup under pressure. Some of the gas
dissolves, resulting in the delightful fizziness that we so enjoy when we consume a carbonated
Please exercise caution when using dry ice. The temperature of the solid
is very low. Dry ice absorbs heat
from its surroundings. You will need to pick up the dry ice with a towel, tongs, or forceps. NEVER TOUCH DRY ICE WITH YOUR BARE HANDS!! Tissue damage or frostbite can result from the improper handling of dry ice.
- Obtain a small piece of dry ice. Place it on the lab counter top. Observe.
What two states of matter are present?
- Place the dry ice in a 50-mL plastic beaker. Tightly cover the beaker with the palm of your hand. What do you experience?
Explain, in terms of molecular motion and kinetic energy, why gas molecules can exert the pressure that you feel beneath your hand.
- Place the dry ice on the countertop. Using forceps, push a coin vertically down into the ice.
Why does the coin vibrate?
Why does icy frost form on the surface of the coin?
- Obtain a piece of dry ice with a flat surface. Using a pencil, slide the block of dry ice across the table. Attempt to have the block of ice come to rest as close as possible to the line taped down to the countertop.
Why does dry ice slide so easily?
Is the block of ice actually on the counter top or is it riding on a cushion of gas?
- Using an eyedropper, make a small (the size of a quarter) puddle of water on the counter. Using forceps, place a tiny piece of dry ice in the puddle.
What do you observe?
- Place several small pieces of dry ice into a clear plastic cup. Cover the cup with your hand to prevent the gas that forms from escaping. Have your partner light a candle. "Pour" the gaseous carbon dioxide over the candle flame.
What happens to the flame?
Based on your observations, is CO2 lighter or denser than air?
- Add enough water to the dry ice in the plastic cup to cover the dry ice. Observe.
What is inside the bubbles that form?
Watch carefully. Once the bubbling begins to subside or slow down, you can notice that the dry ice is encapsulated by a layer of regular ice. The water in the cup will actually freeze around the outside of the dry ice. Add some tap water to the cup. The ice layer will melt and the dry ice will be free to bubble once again.
- Add a few drops of Dawn detergent to the water in the cup. Stir to mix. Dip your fingers into the soapy water and spread a film of soap over the top of the cup. Watch as the carbon dioxide gas expands under the soap film to make a ghostly bubble!
What is dry ice?