<p> Chemistry Demonstrations Dry Ice: candles and stuff in aquarium Materials: Dry ice, candle, lighter, small (5 gallon) aquarium, cardboard piece to cover aquarium, 500 mL beaker. You can generate the carbon dioxide with baking soda and acid if you want. Three 500 mL graduated cylinders, universal indicators.</p><p>Safety: Dry ice is very cold and causes frostbite. Use gloves.</p><p>Set-up: Have an aquarium with a cover. Three graduated cylinders filled with water.</p><p>Procedure 1: Put a big chunk of dry ice in the aquarium. Cover with the cardboard piece. Allow to subliminate for a little while. Discuss sublimination while waiting. Ask a student to tell you when the aquarium is full of carbon dioxide. To determine if the aquarium is full, light the candle. Hold it carefully in the aquarium. When it sinks below the CO2 it will go out.</p><p>Discussion: Why can’t the student tell when the aquarium is full (CO2 is invisible). Why does the candle go out? (no oxygen). Carbon dioxide is heavier than air. Occasionally people are suffocated by carbon dioxide while cleaning out tanks.</p><p>Procedure 2: light the butane lighter. Carefully hold it in the aquarium. At the right level the flame will lift off the lighter and be suspended in space. </p><p>Discussion: Why does the flame become suspended (below the CO2 the butane cannot burn. As it hits the air it burns.)? </p><p>Procedure 3: Light the candle on the bench. Carefully scoop up a beaker full of </p><p>CO2. Ask a student if it is full. Pour the CO2 on the candle. For much greater flair pour the CO2 into another 500 mL beaker and then on the candle (requires some practice). </p><p>Procedure 4: Pour the CO2 from the beaker through a paper towel roll onto the candle. Try a longer tube. Procedure 5: Take large graduated cylinders and fill with water. Add universal indicator. Add some base to turn the color. Add a chunk of dry ice. As it sublimates the color of the indicator changes. Why? (carbon dioxide dissolves to form carbonic acid which lowers the pH. This is happening in the ocean from carbon dioxide pollution and lowering the amount of fish in the ocean.)</p><p>Equation: How many grams of dry ice are needed to fill a 20 liter aquarium? (about 40)</p><p>Topics: Gasses, density, combustion</p><p>Clean-up: put away the aquarium. If you used baking soda wash it out in the sink. Pour out the water in the graduated cylinders.</p>