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ExposeExciteIgniteMay2012

paper or burning of a

paper or burning of a candle. The property required is that of a high rate of chemical reaction. Study Table 10.2 and be prepared to be amazed: Substance Process Internal energy MJ/kg Combustion rate kJ/sec Wood Coal Diesel Gunpowder Nitroglycerin burning 13 3.6 burning 28 7 combustion 46 166 deflagration 2 1,330,000 detonation 4 20,000,000 Nitroglycerin’s impressive combustion rate creates a supersonic air pressure wave and it comes as no surprise that it has a detonation velocity around 7,000 m/sec ! So it is the speed (or rate) at which explosive chemicals combust or decompose that makes all the difference! So much for the physical chemistry. Lets get practical. Safety / Risk Assessment [] Table 10.2 OK. Ammonia Nitrogen Triiodide is an explosive but there is no reason why a qualified science teacher with a chemistry background should not attempt to prepare at least a small quantity of this fascinating compound. The wet nitrogen triiodide complex is relatively safe to handle. However, if allowed to dry it becomes extremely unstable and even air movement can cause an unexpected detonation. ! Never prepare more than is required. The substance cannot be stored ! Only prepare small quantities at a time in an open, easily cleanable container ! Do not move the explosives once positioned. Any disturbance can activate the explosive ! Do not place in direct sunlight as spontaneous detonation will occur ! Put a warning sign up and ensure that no one has access to the explosives area during the curing time ! The detonation noise is loud - use ear protection and urge the audience to cover their ears 113

! The detonation should only be performed behind a safety screen in a well ventilated area due to the formation of iodine vapours. A fume cupboard will be the first port of call ! NEVER try to detonate with bare hands, even in small quantities. Use a long pole and feather (Figure 10.3) Figure 10.3 Chemical Safety ! Use standard safety procedures when handling all chemicals (protective glasses and gloves). Pour the ammonia in a fume cupboard ! Chemicals should be locked away from students Ammonium hydroxide (Ammonia solution) is an irritant with a strong pungent, suffocating odour. Only use in a well ventilated area. • Risk phrases: R36/37/38 Irritating to eyes, respiratory system and skin. • Safety phrase: S2/3/26 Keep out of reach of children; Keep in a cool place; In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. Iodine crystals are poisonous and produce a corrosive vapour. They are intensely irritating to eyes, skin and mucous membranes. • Risk phrases: R20/21 Harmful by inhalation and in contact with the skin. • Safety phrase: S23/25 Do not breathe vapour; Avoid contact with eyes. What you will need Chemicals • Iodine crystals: I2 (do not use Tincture of Iodine) • Ammonia (aqueous solution): 15M NH4OH, 25 to 35% solution You may use household Cloudy Ammonia which usually is an 4% ammonia solution but much better results are obtained with a “concentrated” ammonia solution. Equipment • Glass beaker, 100 ml • Spatula • Retort stand • Ring clamp • Masking tape • Filter paper • Feather duster or single feather taped to a stick (Fig. 10.3) • Safety gloves • Protective goggles & Ear muffs 114