They will say the balloon popped, and that it made a sound, but ask them if there is anything else they should comment on. Using the lit candle on the meter stick, carefully touch the blue balloon filled with helium with the flame. In order to test the hypothesis that the balloons contain helium, inform them of the fact that hydrogen is a flammable gas while helium is not. Mention these are the first two elements in the periodic table, and show this if a table is available. Ask them if this is the only possible gas the balloons can contain - more informative people may mention hydrogen. Ask them to comment about their buoyancy - they may volunteer that the balloons are filled with helium, based on previous experience. When asked about the colors of the balloons, audience members usually are not specific about what they see - reinforce the fact that there are a specific number of red, yellow and blue balloons - not all balloons are all colors - this is important to emphasize so that know the importance of good observations in experiments. Since the demonstrator is the closest to the balloons and loud sounds are generated, ear protection is strongly recommended.Īsk the audience to make observations and to make comments about the six balloons. A source of flame is prepared - a stationary candle in a glass holder can be lit with a barbecue lighter which can be used to light the birthday candle on the meter stick, or the barbecue lighter can be used exclusively - experience has shown the stationary candle preparation provides a smoother demonstration flow. A birthday candle is attached to a meter stick or metal rod. Each of the floating balloons is placed on a lab bench ca. The yellow balloons are filled with hydrogen, and the red balloons are filled with a 2:1 mixture of hydrogen and oxygen - each balloon being secured in the same manner as the helium balloons. The blue balloons are filled with helium, tied off and attached to the strings attached to weights - plastic balloon closures can be used to attach the balloons to the strings. Sources of helium, hydrogen and oxygen should be available. 1.5 - 2.0 m lengths of string attached to weights. Six balloons (two red, two yellow, and two blue - colors can vary) are prepared along with ca. The explosions are caused by a sudden pressure effect through the action of heat on produced or adjacent gases. The comparatively mild sounds emitted when the helium balloons are ignited are caused by the rupturing of the balloons and the escape of the gas. When pure hydrogen is ignited, the reaction with the surrounding air is less rapid, the sound is less loud, and a significantly larger flame is produced. The rapid release of a considerable amount of energy causes the surrounding air to expand suddenly, resulting in a sharp expolsion. This exothermic reaction yields 232 kJ/mol of water formed. When ignited, hydrogen gas combines with oxygen gas explosively in proportions ranging from 4.1 - 71.5% hydrogen - ignition temperature is ca. Illustrates the properties of lighter than air gases and mixtures, and provides an opportunity to show students various aspects of the scientific method. Different intensities of sound are emitted, with the loudest sound occurring when a hydrogen/oxygen mixture is ignited. Six balloons are filled with different gases and ignited.
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