Oxidation is the loss of electrons. Oxidation occurs when gunpowder explodes, it contains carbon, sulphur and potassium nitrate. The carbon and sulphur are both oxidised to form gases. The potassium nitrate carries oxygen, meaning it is an oxidising agent and gunpowder carries it’s own oxygen supply for the reactions. This makes the explosion very powerful as the oxygen is available as soon as the gunpowder is ignited.
C(s) + O2(g) –> CO2(g)
The carbon gains oxygen and it’s oxidation number increases from 0 to +4 making CO2. Oxidation means there is a faster reaction as there are oxygen molecules to react with. The more oxygen molecules the more violent the reaction.
Gunpowder was the first explosive used, it was a good explosive as it contained it’s own oxygen supply. It was made of carbon, sulphur and potassium nitrate (the oxidiser). However it produced large quantities of white smoke so wasn’t effective as a weapon as it obscured the opposition.
Cellulose nitrate was then produced by reacting cellulose with nitric acid and sulphuric acid. This did not produce smoke when it exploded so the visibility on battlefields was improved. A fuse wasn’t needed as cellulose nitrate could be ignited by percussion, and larger quantities could be used. To use as an explosive cellulose trinitrate and nitro-glycerine were mixed together. Propanone was then used to produce a jelly-like substance out of the mixture. This jelly can be squeezed through holes to produce cords which is why it is called a propellant.
The next explosive produced was nitro-glycerine which is produced by heating glycerine with concentrated nitric acid using sulphuric acid as a catalyst. The OH groups found in the glycerine are converted into nitrate groups, this is a nitration reaction. This was a very effective and powerful explosive, however, it was very unstable, meaning it was dangerous. To make it stable nitro-glycerine was mixed with kieselguhr, an inert substance. This was much more effective, as it could now only be ignited deliberately. It could be shaped into sticks that was called Dynamite 1, gunpowder was used to give out energy to ignite the nitro-glycerine. To make the gunpowder explode a percussion cap was used. Dynamite 2 was even more effective as it was more violent, the nitro-glycerine was mixed with substances which actually burnt on their own, making it very powerful.
The most recent explosive is TNT which contains nitro groups instead of nitrate groups. It doesn’t react with metals so can be transported and carried easily.
High Explosives and Low Explosives
For an explosive reaction to occur energy has to be given out and therefore it must be exothermic. For this to happen the energy given out to the surroundings when bonds form has to be greater than the amount of energy taken in when bonds become broken.
The strength of the explosive depends on the energy difference made between making and breaking bonds. The greater the difference the more forceful the explosion.
For it to be an effective explosion the reaction must take place immediately so that the majority of energy is given out at the same time. When gaseous products are made the pressure inside casing increases greatly, this added pressure creates an explosion. This pressure is produced as the reactants take up very little space as they are manly solids, the gases take up so much more space and so need to escape from the casing. For example, when nitro-glycerine burns the number of moles taken up by the gases is much more than that of the liquid:
C3H5N3O9(l) –> 3CO2(g) + 21/2H2O(g) + 11/2N2(g) + 1/4O2(g)
1 mole of liquid –> 7.25 mols of gas
Nitro-glycerine is an example of a high explosive as it rises up to 275000 atmospheres in microseconds. However, low explosives only create a small amount of pressure compared to nitro-glycerine (6000 atmospheres in milliseconds).
The way propanone has been manufactured has changed several times. It was first produced from the dry distillation of wood but it was very unproductive. It was then manufactured by bacterial fermentation of starch in maize, however, it was needed for food and was too much in demand and was also quite a slow process, so they had to start using conkers which weren’t in demand.
After the war propanone was made by passing the propan-2-ol vapour over a copper catalyst at 500(C and 400kPa. This high temperature and pressure means that this way is very productive as it is a fast process, also made faster by the use of a catalyst.
Health and Safety
Experiments did not follow safety regulations , for example, Ascanio Sobrero was cut with pieces of glass on his hands and face, showing that no safety controls took place, such as goggles and a lab coat. Sobrero also tasted the chemicals he produced to see how harmful they were, and suffered side-effects.
Experiments were not carried in controlled labs, but in homes, as a German scientist spilt some acid on a piece of clothing whilst he was completing an experiment.
People who worked in factories were not properly cared for as they suffered from headaches and anaemia showing that they were given the correct equipment to protect them from the harmful effects of TNT.
Nobel’s brother was killed as a result of the experiments, so the further experiments needed to be carried out on a barge. This meant that if there was an accident then not many people would die from it and the damage would be limited.