- Give an account of the development of chemical compounds for use in explosives. Describe the advantages of each new chemical explosive over its predecessors, and describe how the explosives were adapted to make them safer and more effective. [9]
The very first discovery of an explosive chemical compound was unintended.
In 1846 Dr Christian Schönobein accidentally spilled concentrated sulphuric and nitric acids; he quickly cleaned the contaminated area with an apron made of cotton. Knowing that the apron would soon be destroyed by the acids, he rinsed it out with water and hung it up to dry in front of the fire.
Moments later the cloth burst into flames. Dr Schönobein was not aware that he had discovered “gun cotton” otherwise known as Cellulose Nitrate or Nitrocellulose. From 1860s onwards the military began investigating the possibilities of cellulose nitrate as a smoke-free gunpowder.
Towards the end of the nineteenth century, black powder had been replaced as a propellant for military purposes by a smokeless powder based on cellulose nitrate. This substance catches fire very quickly and burns without lighting a fuse; produces very little smoke and creates an impulsive impact. Therefore, explosive shells were replaced by cannon balls and bullets replaced musket balls.
This smokeless powder used by the British Army is called cordite and was invented in 1880s. It consists of Cellulose Trinitrate and Glycerol Trinitrate amongst other substances. This substance catches fire very easily and burns quickly.
The powder was transformed into a jelly-like substance by adding an organic solvent propanone. This smokeless powder is now used worldwide as a military propellant.
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In 1847 an Italian scientist, Ascanio Sobrero was experimenting with concentrated acids. He combined together nitric, sulphuric acids with glycerine. The new substance formed was a yellowish oil. He had discovered Nitroglycerine. He experimented with a small sample and realised that was extremely unstable. Its behaviour was unpredictable. It could be detonated by the touch of a feather.
Immanuel Nobel and his son Alfred Nobel from Sweden were responsible for controlling Nitroglycerine. Nobel made a deliberate explosion by mixing Nitroglycerine with (kieselguhr) which is a silica based mineral. He made a paste which could be shaped into rods. These would only explode when they are intentionally detonated. These are the very first safe high explosives.
Nobel developed even safer ways to detonate these explosives. He found out that the most reliable and effective way to set off nitroglycerine was to use small quantities of gunpowder.
He also invented the first percussion cap that gives out a small explosion when it is given a sharp impact. The caps were filled with a compound known as fulminate of mercury Hg(CNO)2. This substance is very sensitive that even a finger tap can cause it to detonate. This ignites the gunpowder or other explosives.
In 1867 Nobel patented his dynamite. It was called Dynamite No 1.
He soon realised that very effective mixtures could be made by replacing the inert kieselguhr by a substance that would itself burn or explode.
He combined nitroglycerine with charcoal, barium nitrate and sulphur which led a new explosive product in 1869. It was called Dynamite No 2.
This product was suitable for use in quarries and coal mines.
Nobel patented another explosive product in 1875. He added 7 to 8 per cent of collodion (nitrated cellulose) to warm nitroglycerine forming a stiff jelly-like substance known as blasting gelatine. This product proved to be more powerful explosive than dynamite, because both nitroglycerine and collodion were explosive.
During the Second World War, Trinitrotoluene (TNT) was developed. TNT contains nitro groups (NO2). It doesn’t react with metals therefore can be used in metal containers to produce bombs.
TNT causes headaches, anaemia and skin irritation. Subsequently, workers in factories often suffered health problems.
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- Discuss, with reference to high and low explosives, the ideal features of an explosive reaction, explaining, with examples, how chemical reactions produce energy and how they cause increase in pressure. [6]
Nitroglycerine is acknowledged as a high explosive. It produces a large volume of hot gas. Its decomposition only takes microseconds at a pressure of 275 000 atmospheres.
Black Powder and Cellulose Nitrate are considered as low explosives. They produce a large volume of hot gas. The decomposition takes millisecond at a pressure of 6000 atmospheres.
An ideal explosive reaction must take place very quickly. It must be an exothermic reaction where heat is given out. The products formed must mainly be hot gases produced in a confined space. This leads to a big rise in pressure which is the main cause of the explosion.
- An equation for explosion of nitroglycerine
C3H5N3O9 (l) 3CO2 (g) + 2½H2O (g)
+1½N2 (g) + ¼O2(g)
1 mol of liquid 7.25 moles of gas
No oxygen supply from air was needed for the reaction. The exact products are based on the actual explosion. In an oxidation reaction oxides of nitrogen such as (NO and NO2) may be produced. The amount of heat energy released from a nitroglycerine explosion is 6275 KJ kgˉ1. The increase in pressure will produce greater energy from the explosion.
- Describe how UK methods of manufacture of propanone have changed since the beginning of the First World War. [3]
Before the war propanone was manufactured by dry distillation of wood in a process that excluded air. This method was very inefficient.
In 1914 a Russian chemist, Chaim Weizmann, developed a new process that produced propane by bacterial fermentation of starch in maize. This process was capable of producing 30 000 tonne.
After the war propanone was manufactured from propan-2-ol by passing the vapour over a copper catalyst at 500°C and 400kPa. Propanone was produced from propene, a product of catalytic cracking of crude oil fractions.
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- Discuss how attitudes to health and safety in chemical research and industrial chemistry have changed over time. Use examples from the history of development and manufactures of explosives and medicines. [4]
The discovery of cellulose nitrate was a hazard of health and safety.
The discovery of nitroglycerine was another major hazard as it its behaviour was very unpredictable. Its discoverer Ascanio Sobrero was badly scarred as a result of an unexpected explosion that spattered glass fragments into his hands and face. He said “victims killed during nitroglycerine explosions”
He was ashamed to be the inventor of such a deadly explosive.
In Nobel’s nitroglycerine factory, there was an explosion that killed his young brother Emil and another chemist.
However test on animals showed that nitroglycerine causes blood vessels of the brain and heart to flow with blood. Nitroglycerine was considered a possible treatment.
Nitroglycerine is effective for treating angina pectoris; intense pain in heart. A medicine known as amyl nitrate similar to nitroglycerine are used as treatments to this day.
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Name: Mohammad Ahmed
Candidate No.
