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• Water cooler for

• Water cooler for cooling the bottle. A beaker or cut-off plastic milk container will do. Check that the glass bottle fits into it • Plastic funnel (to fit bottle) • Teaspoon • Thin candle taped to a dowel stick • Ear protection, goggles, lab coat & gloves Here’s how 1. Fill the glass bottle up to one third of its volume with water. Do NOT use a plastic bottle! 2. Stand the bottle in the container of water to cool the exothermic process and protect the bottle from cracking (Figure 3.4). The container water level should be at least the same as the level inside the bottle. 3. Safety glasses and gloves on! Carefully add three heaped teaspoons of caustic soda to the water in the bottle using the funnel (Figure 3.5). Be sure to close the caustic soda container as caustic soda is hygroscopic (absorbs moisture from the atmosphere). Do not seal the glass bottle. Figure 3.4 Figure 3.5 4. Swirl the bottle gently until all the solids have dissolved. Take care not to slosh any solution from the bottle. [Note that the solution will get hot as the dissolution of sodium hydroxide is an exothermic process]. 5. Tear three sheets of aluminium foil, each approximately 20 cm x 30 cm (8” x 12”). Tear each sheet in half and roll into a cylinder so it will easily fit through the mouth of the bottle (Figure 3.6). Pop them into the bottle. 27

Figure 3.6 Three sheets should be sufficient to launch one large balloon. 6. Inflate a balloon once to stretch it, let the air out and pull the balloon over the mouth of the bottle, while someone else holds the bottle steady. Gently swirl the foil and solution a few times and place the bottle back in the water container. 7. The balloon will slowly fill up with hydrogen gas (H2) (Figure 3.7). Draw the students attention to the exothermic process, the colour change of the solution (sodium aluminate) and the formation of gas bubbles. 28 Figure 3.7 Safety: It is important that the caustic soda solution should not get too hot as this will produce water vapour in the balloon that will add