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In a chemical reaction, matter is neither created nor destroyed-except in this discrepant event demonstration! Let students discover what is really measured when something is “weighed” on a balance. First carry out a gas producing reaction in a capped bottle to verify the law of conservation of mass in a chemical reaction. When a balloon is substituted for the cap, the balloon captures the product gases and is supported by buoyant forces in air. The mass decreases as the balloon fills up! The apparent mass discrepancy should help students understand the difference between “weighing” and “massing.” Enough materials are provided to perform the demonstration seven times.
Concepts: Conservation of mass, buoyancy, mass versus weight.
Time Required: 15 minutes
Materials Provided: Acetic acid, sodium carbonate, balloon, 1-L bottle and cap, weighing dishes.