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As most of us can still recall from our science lab days, matter exists in three states: solid, liquid and gaseous. In fact the same substance can exist in all three states, if the conditions are right. The most common example used is water, which can be a solid when frozen, a liquid at most temperatures and a gas once it reaches the boiling point.
But there is another substance we can obtain readily from an ice house or packing plant that also can exist in different forms- solid carbon dioxide, better known as dry ice. This unusual and fascinating material serves several useful purposes as a freezing agent and food preserver, but can also be the focus of many experiments and fun projects. If you can obtain a supply of dry ice and the safety equipment necessary to handle it (heavy gloves, eye protection, tongs), here are some very interesting experiments you and your children can try at home.
1. Smashing dry ice with a hammer. This little experiment can explain the transformation of matter from one state to another. Explain to your child that dry ice is a solid form of carbon dioxide, which is usually found in gas form. Take a small portion of dry ice and place it on a very firm surface, like a concrete slab or flat stone. Explain to your child that sometimes solids change into gases without going through a liquid stage. Strike the piece of dry ice with a hammer and see what happens next.
2. Freezing objects far below 32 degrees Fahrenheit. This is a popular experiment with children, because of the spectacular and largely unexpected results. Explain to your child that dry ice is much colder than the ice cubes in the freezer at home. Frozen carbon dioxide doesn't reach Absolute Zero, which is the coldest any object can get, but it does come fairly close.
Take some common household items such as flowers, fruits, rubber balls, balloons, or whatever you find that can withstand freezing. Place these objects in an insulated cooler filled with dry ice, and leave them undisturbed for several hours.
Wearing eye protection and heavy gloves, carefully use tongs to remove the items one at a time for inspection. Ask your child what he or she thinks might happen if you strike the object against a hard surface. After your child has offered his opinion, forcefully strike the various objects on a hard surface, making sure that everyone is at a safe distance. Compare the results with your child's predictions.
3. Balloons that inflate themselves. Place a small amount of dry ice inside a latex balloon and tie it securely. As the solid begins to turn into gas, the balloon will inflate by itself.
4. Homemade fire extinguishers. You can explain the heaviness of carbon dioxide gas by setting up this experiment. Place a candle inside a pyrex glass measuring cup. Use a small birthday candle, and sand to hold it upright. In another container place some dry ice in some water to create fog. Light the candle. Carefully 'pour' the fog over the candle, making sure not to spill any actual liquid. Explain to your child that the gas in the fog is heavier than air, so it wants to sink into the glass. When the gas reaches the candle flame, it chokes out the oxygen that the candle needs for fire. The candle goes out. This is the same thing that some fire extinguisher do to put out fires- they make carbon dioxide gas that smothers out the oxygen a fire needs to burn.
5. Create an entire room of fog. No Halloween party would be complete without a spooky atmosphere filled with fog. Obtain several large tubs that will hold water, and place a substantial amount of dry ice in each just before the party. Make sure the room has plenty of ventilation. Within minutes, your room should fill up with rivers of fog, which will add just the right amount of atmosphere to a haunted house party.
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