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ExposeExciteIgniteMay2012

Disposal & Clean-up Do

Disposal & Clean-up Do not store the caustic soda solution. Dispose of it and any residue from the reaction down a toilet – this does not pose a hazard as caustic soda is the active ingredient in most drain cleaners. Rinse the bottle with water. Teaching Extensions Here are a few suggestions to challenge interested students: 1. Looking at the H2 preparation, 2Al (s) + 2NaOH (aq) + 2H2O ! 2NaAlO2 (aq) + 3H2 + energy ! Where did the NaAlO2 go? ! How would the addition of finely cut aluminium foil change the rate of the chemical reaction? 2. Why does the filled balloon shrink after a few hours, so much so that it no longer floats? Students can investigate ‘effusion’. According to Graham’s Law the rate at which gases effuse is dependent on their molecular weight. Gases with a lower molecular weight effuse more quickly than gases with a higher molecular weight. Compare the rate of effusion of two balloons filled with He and H2. 3. What is an exothermic reaction? Can students identify the two exothermic reactions here? Water & caustic soda and caustic soda & aluminium. 4. Compare the hydrogen and butane combustion reactions: 2H2 + O2 ! 2H2O + energy 2C4H10 + 13O2 ! 8CO2 + 10H2O + energy ! What impact will both reactions have on issues such as global warming and our sustainable environment? ! Emphasize the need for oxygen in both combustions. Note the molar ratios of fuel to oxygen. ! Where did the H2O go when the H2 balloon was ignited? Key Terms Combustion, balancing of chemical equations, effusion, activation energy, exothermic reactions, hydrogen gas, sustainable energy 31

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