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# ExposeExciteIgniteMay2012

## It also tells us that

It also tells us that there is no use in adding more fuel, if oxygen is not supplied too. The equation states that two moles of butane reacts with thirteen moles of oxygen. Or 2/13 = 0.15 moles butane reacts with one mole 0f oxygen. As the Ideal Gas Law is closely obeyed by nearly all gases at room temperature and standard pressure, the ratio of 0.15 : 1 should thus apply to the volumes of the gases too. The amount of oxygen in our 500 ml can is set. Air contains 21% oxygen therefore: 21% of the volume of the can: 0.21 x 500 cm 3 = 105 cm 3 oxygen therefore requires: Volume ratio: 105 x 0.15 = 15.8 cm 3 butane. butane volume : air volume 15.8 : 500 1 : 32 So, for butane you may simply divide your can’s volume by 32 to calculate the volume of butane required. Even if you work in fluid ounces. Of course, if you use other fuel types the ratio will change. For propane (C3H8) C3H8 + 5O2 ! 3CO2 + 4H2O + energy we have 0.20 moles propane reacting with 1 mole oxygen and following the same reasoning as above, the propane : air volume ratio becomes 1 : 24. By the way: The ideal fuel-air volume ratio for petrol (gasoline) in motor car engines is 1 : 14.7 but this will change depending on the type of fuel. A. The Barking Bunny 1 Can [] Now let’s get on with the practical side. We will use a simple approach so that the device can be made in minutes. We are after a demonstration that is reliable, safe and easy to produce. Safety / Risk Assessment " The combustion process produces heat and expanding Figure 2.3 1 The bunny refers to the trade marked and universally well-known Nesquik ® bunny. 15

gas, so expect a loud noise and a fast moving lid. The lid should be tied down with fishing line as instructed below. You should wear eye and ear protection and caution the students to protect their ears. Do not launch any projectile at glass objects, animals or people. " Furthermore - take general precautions when drilling metal and be on the lookout for burrs and sharp edges. What you will need • One 250 g Nesquik ® can (or similar can with a metal press-lid) • Measuring cylinder / cup • Fire lighter with round shaft • Drill and drill bit with diameter same as fire lighter shaft • Butane refill can (used for refilling of gas lighters, at tobacconist shop) • Plastic syringe (20 mL or 0.7 oz) - no needle • Fishing line (strong!) approx. 1 m (3.3’) • Cable tie that will fit around the can. • Poking tool, awl or nail • File or sand paper Here’s how 1. Clean a Nesquik ® can (or similar metal can). Figure 2.4 2. Measure and record the volume of the can using water and a measuring cylinder / cup. 3. Poke or hammer a hole into the centre of the base with the poking tool or nail (Figure 2.5). 4. Enlarge this hole to the diameter of the gas lighter shaft with the hand drill (Figure 2.6). The lighter shaft should fit tightly through this hole (Figure 2.7). This can be done with long nose (pointy) pliers too. 16 Figure 2.5 Figure 2.6