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ExposeExciteIgniteMay2012

unnecessary weight to

unnecessary weight to the balloon and prevent it from floating. The reaction rate has to be slowed down. Here are some recommendations: • Do not add more than 3 heaped teaspoons of caustic soda • Do not add more than 3 rolled aluminium sheets at a time • Cool the reaction mixture in cold water using a beaker or trough • Let the bottle and its contents cool before filling the next balloon 8. When the balloon is filled to its maximum capacity or if the reaction in the bottle ceases, gently remove the balloon from the bottle while someone else holds the bottle steady. Take care - the bottle will be very hot. 9. Secure the balloon clip to the balloon base and check that no gas can escape. To fill another balloon: Wait a few minutes for the solution to cool, add more caustic soda and repeat the procedure. The inflated balloon should rise - if not, then ! the balloon might contain too much condensed water. The reaction proceeded too quickly – repeat the process by replacing the cooling water and reducing the concentration of the caustic soda ! the balloon might not be filled to its full capacity. Add more reagents next time Ask students what the identity of the gas is and invariably they will reply “helium”. So this may be the moment to demonstrate “helium’s” inertness by making it react violently with atmospheric oxygen. There are many things to do with hydrogen balloons. Turn to the next chapter to see what your options are, or simply explode them as described in the next activity. Making the hydrogen accessible Here is a novel way to deliver the prepared hydrogen “on demand”. Source an air tool known as an air pistol blowgun at a tool or hardware shop. They are used for cleaning equipment with compressed air and only cost a few dollars. You will need to purchase a clip-on connector also so the balloon can fit onto the blowgun (Figure 3.8). Figure 3.8 We will use this device in the next chapter. 29

B. Exploding a Hydrogen Balloon [] This is the fun part that most students love, but also the more hazardous part. Do plan this carefully. The biggest potential hazard is the possibility of igniting other chemicals or combustible substances. The explosion can be loud but no solid shrapnel pieces are produced. Here’s how 1. Tie the hydrogen balloon’s string to a table, chair or other structure away from combustible material (Figure 3.9). 2. Tape a thin candle securely to a wooden dowel. This will allow you to ignite the balloon from a safe distance (Figure 3.10). 3. Light the candle. Safety: Warn all bystanders to stand off (at least 5 m) and to protect their ears. Wear safety goggles and ear protection. Have a fire extinguisher on hand. Figure 3.9 4. Use the lit candle at arm’s length to ignite the bottom of the balloon . . . BANG !!!! Bang! Candle taped to dowel Figure 3.10 30