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ExposeExciteIgniteMay2012

chemicals are very

chemicals are very stable. But seal the container well to keep the air moisture out. If you want to, dissolve the unused propellant in water and wash it down the drain. Teaching Extension The Reaction Products Here are some interesting questions related to the rocket’s combustion reaction. Have students study the reaction C12H22O11 + 6.3KNO3 ! 3.8CO2 + 5.2 CO + 7.8H2O + 3.1H2 + 3.1N2 + 3.0K2CO3 + 0.3KOH and then ask . . . • Why does the rocket produce a purple (lilac) coloured flame? Burn a small quantity of the propellant in a fume cupboard to see the colour. (Potassium flame) • What are the names of the compounds that showed up as smoke? (K2CO3 & KOH) • Are the smoke compound(s) gases or solids? (Solids) • What happened to the CO2 ; CO ; H2O ; H2 ; N2 ? Are they visible? (They are gases and are invisible just like the surrounding air) • Is there an increase in entropy (#S)? (Huge increase as 23 moles of gas are formed from 1 mole sucrose) • Is this an endothermic or exothermic reaction? (Exothermic) • Which of the reaction products would cause pollution concerns if this propellant were to be used to propel commercial rockets? (Green house gas CO2 & caustic KOH) • What was the real origin of the energy released in the propulsion reaction? (The sun. The surplus exothermic energy produced in this reaction originated from the rearrangement of the bonds in the sugar and nitrate molecules. The sugar chemical potential bond energies were established during the process of photosynthesis in the sugar cane, powered by solar energy. This is true for all bio- and dino-fuels) 105

B. Prepare Fire Paper [] If sucrose can act as a fuel, how about a similar organic product such as cellulose? To answer this, we can try an old chemistry trick that links up nicely with saltpetre and its use as an oxidant. You may have seen it before - a blank piece of paper burns in a predetermined pattern along an invisible line. Prepare the paper 1. Dissolve 2 teaspoons of potassium nitrate in 50 mL (1.7 oz) water. If all solids do not dissolve - no problem. 2. Take a sheet of paper or news paper (preferable) and write your name on it with a glass rod or a cotton ear bud dipped in the saturated solution. Use continuous (cursive) writing and link the name and surname with a line. Use the liquid liberally and mark a spot where you want to start the fire. 3. Leave to dry at room temperature. 4. Place on a fire resistant surface. Light a match, blow out the flame and touch the marked spot with the glowing tip (Figure 9.14). Watch your name go up in smoke! Figure 9.14 The Fire Race is on A much faster combustion is attained with paper towel. If you have access to a continuous roll of paper towel, use it for a flaming poster for the school open day. Give all a warm welcome by setting the words “Hot Chemistry!” alight. In Figure 9.14 we started a “fire race” on a piece of newspaper. You can 106