Chemistry Report on Explosives
What is meant byoxidation and show how oxidation reactions are used to cause explosions.
Oxidation is the term used for the combinationof a substance with oxygen, or in general any reaction where an atom ormolecule loses electrons.
This can be shown as:
C(s) + O2 (g)CO (g)
S=solid, g=gas
Gunpowderor black powder is the oldest explosive we know. It is made up of a mixture ofpotassium nitrate (also known as saltpetre or KNO3), charcoal, andsulfur in different proportions. When gunpowder is manufactured today, it ismade with the ratios 7.5:1.5:1 by mass (2).
Bothgunpowder and dynamite have within them substances which are readily availableto oxidation. The oxygen which is used for the oxidation is an intrinsic partof the mixture, and is held within them in the same manner that oxygen isstored in the chemical potassium chlorate.
Whengunpowder is ignited, this oxidation is extremely rapid, and a large volume ofgas is produced. The gasses are under extreme pressure, which causesthem to expand rapidly. Heat is produced causing the gas particles toaccelerate, creating even more pressure. If the gas expands faster than thespeed of sound, this creates a shockwave. The pressure produced by the gassesis what causes parts of the bomb (shrapnel) to be propelled far and wide atvery high speeds(1).
Thespeed at which something oxidises is dependant on its potential to interactwith oxygen. The greater number of unstable electrons that a molecule or atomhas to lose, the quicker it will be oxidised (3).
b) Give an account of thedevelopment of chemical compounds for use in explosives. Describe theadvantages of each new chemical explosive over its predecessors, and describehow the explosives were adapted to make them safer and more effective. (9marks)
It is thought that the firstexplosive discovered was ‘black powder’, originating in 10th Century China. Itwas used for ceremonial fireworks. In Europe, 1242 saw the formula for blackpowder being published by Roger Bacon. The refinement of the substance closelyfollowed after the gun was invented by Berthold Schwartz in 1300. Around thistime, black powder was being used for removal of rocks, the teqnique was knownas fire setting, but this was replaced with blasting at the beginning of the17th Century. There are records of blasting in America from 1773 (4).
The production of black powderwas rapidly increased during the American Revolution. By the turn of thecentury, the commercial production of the explosive had grown from 25 millionto 100 million (2).
In 1846, Nitroglycerin wasdiscovered by Ascanio Sobrero. Nitroglycerin plasticizes collodion which is aform of nitrocellulose to form blasting gelatin. This is a very powerfulexplosive. The discovery of this action led to the advancement of ballistite, thefirst double-base propellant and a precursor of cordite.
Alfred Nobel built a factory toproduce it in 1861 in Sweden. An advantage of nitroglycerin was its massiveexplosive power, but it was very difficult to transport as it is a liquid,which used black powder to ignite it. It could also freeze and had toxic fumeswhich caused severe headaches (5).
In 1867, Nobel accidentallyinvented Dynamite and he went on to patent his mixture. It was a greatdiscovery, being more powerful than black powder, with a higher detonationvelocity which made it much more effective breaking rock as it not only moved,but broke apart the rock
Ammonium nitrate was initially synthesizedin 1659 by J. R. Glauber by blending ammonium carbonate and nitric acid. It wasmostly used for fertilizer and blasting and to replace a portion ofnitroglycerin in dynamite (1).
Dupont introduced Nitramon in1935. This was seen as a breakthrough. They had safe handling, were inexpensiveand did not cause health problems.
It was known as ANFO (AmmoniumNitrate & Fuel Oil) when it was developed in 1955. During its production itcaused a large Texas City explosion. It was easy to load and transport andcheaper than dynamite, it is not a Class A explosive until mixed, but itsaction could be decreased by water. Over 2.2 billion pounds of it were producedin 1974.
Water gels were developed from researchto solve the water problem with ammonium nitrate products (early 1940s). Themarket was small though as most applications needed a small product and therewas no economical sensitizer was not available.
c) Discuss, with reference to highand low explosives, the ideal features of an explosive reaction, explaining,with examples, how chemical reactions produce energy and how they causeincrease in pressure. (6 marks)
There are three categories of explosives: high explosives,primary explosives and low explosives. Gunpowder is a low explosive so thereaction occurs slowly. Expanding gasses are used to propel, not destroy, suchas bullet propulsion from a gun (3).
In high explosives, destruction is caused by the expandinggasses, and the extreme pressure causes a shockwave, if the gas expands morequickly than the speed of sound. The shockwave contributes to the demolitionpower of trinitrotoluene (TNT).
Primary explosives are intended to explode not burn. Theyare used for fuses and blasting caps to initiate an explosion. Shockwaves are acrucial factor in explosions. It is a wave formed from a zone of enormously highpressure in a fluid, including the atmosphere that travels faster than the speedof sound. It moves from the point of the explosion carrying energy and has a severedamaging effect on solid objects it bounces off (5).
In the chemical reaction of the explosion, compounds are brokendown to form various gases. The original chemical compounds (reactants) have muchenergy stored up as chemical bonds between atoms.When molecules break apart, the products (gases) may use some of this energy toform new bonds. Most “leftover” energy takes the form of extremeheat.
d) Describehow UK methods of manufacture of propanone have changed since the beginning ofthe First World War. (3 marks)
Propanone isalso known as Acetone, 2-propanone, methyl ketone and dimethyl ketone. It hasthe chemical formula:
(CH3)2C=O.
Prior to theFirst World War, it was manufactured by hydration of propene from crackedgases. This was revolutionized during WW1 when the chemist Chaim Weizmann showed that propanone could beproduced by the bacterium Clostridium acetobutylicum, this was acontinuation of the studies originally performed by Louis Pasteur showingfermentation was promoted by microbes in the 19th century (2).
e) Discuss how attitudes to health and safety in chemicalresearch and industrial chemistry have changed over time. Use examples from thehistory of the development and manufacture of explosives and medicines.(4marks)
In modern times, we have a numberof health and safety legislations which govern the manufacturing and use ofexplosives for their various purposes. One example is the 1996 USA Departmentof Commerce directive on the manufacturing of fireworks and explosives (6).There are now very tight regulations ensuring that everyone working in thesector is protected as far as possible. It is also accepted that the companiesinvolved have responsibility to protect their workers from harm and mustprovide safety equipment (3).
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Historically there have been huge numbers of accidentsduring explosive production. At one gunpowder mill in the early 19thcentury, situated in Roslin, Scotland, explosions killed two men shortly afterthe mill opened in 1805 and three more were killed by 1815. Many more followed.Deaths caused during the manufacturing process would have numbered greatly asthis was just from one of the thousands of mills worldwide during a shortperiod.
Old attitudes focused on worker responsibility, were nowresponsibility should be shouldered by the company also.
Conclusion
Explosions are due to combustionwhich involves the use of the oxidation process. Depending on how available thesubstance is to interact with oxygen will depend on how quickly it is oxidised.The more quickly it is oxidised, the more quickly the gases will expand and themore devastating the explosion will be.
References
Chang, Raymond, General Chemistry: The Essential Concepts 4th Edition 2004
Kotz, John C., Paul M. Treichel, and Gabriela Weaver Chemistry and Chemical Reactivity 6th Edition 2003
Spencer, James N., George M. Bodner and Lyman H. Rickard Chemistry: Structure and Dynamics 3rd Edition 1999
Infelta, Pierre Introductory Thermodynamics 1st Edition 2005
Smith, E. Brian Basic Chemical Thermodynamics 5thEdition 2004
USA Department Commerce, 009, Manufacture of Fireworks June 2002
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