During the summer holiday, my family and I visited a large cave in the Malaysia. The cave was a famous tourist attraction as there were thousands of bats living in the cave. As we walked along the elevated walkway in the cave, the guide began to talk about the history of the cave. He said that in the past, people used to collect guano in the cave. As he said that, the guide shined his flashlight on the cave floor, and I realised that I could not see it at all, as it was covered in a thick layer of bat feces. The guide then explained that people collected guano for fertiliser and even used it to make fireworks. After he said that, I thought why would people want to go all the way to a cave just to collect bat droppings for fertiliser, and how can bat droppings be used to make fireworks. When I returned to Shanghai, I decided to do some research to find out what chemical properties of guano made it such a valuable fertiliser and how could it be used to make fireworks.
Based on my research, I found that the reason why guano could be both a fertiliser and a component in explosive is because of the rich amounts of various nitrates (NO3– )in it. Nitrates are polyatomic ions that have a trigonal planar structure, with the nitrogen atom as the central atom.
As mentioned earlier, guano was valued as an extremely efficient fertiliser because of the high amounts of nitrates in it. (Wikipedia). Nitrates contain nitrogen, which is an extremely important element for not only plant life but also other organisms as well because it is the main component of amino acids and nucleic acids, which is used to make DNA and other essential proteins. However, the element nitrogen itself cannot be broken down and used by plants as nitrogen molecules are held together by extremely strong triple bonds. Therefore, nitrogen has to be reduced into various nitrates. This is why nitrates have a negative charge to indicate a gain of electrons. Plants get these nitrates naturally from the soil. By adding fertilisers such as guano, the nitrate concentration of the soil increases, therefore increasing plant growth. These nitrates include potassium nitrate KNO3 , sodium nitrate NaNO3 and others. However, though guano used to be mined and collected in the past, today these nitrates are produced synthetically. For example, potassium nitrate is produced when sodium nitrate and potassium chloride are reacted together in a decomposition reaction.
NaNO3 (aq) + KCl (aq) → NaCl (aq) + KNO3 (aq)
Sodium nitrate is produced in a acid-base reaction with nitric acid and soda ash
2 HNO3 + Na2CO3 → 2 NaNO3 + H2O + CO2
However, while fertilisers containing nitrates greatly promote agricultural growth, the excessive use of them has a negative impact on the environment. When the excess fertilsers get washed away into freshwater lakes and rivers, eutrophication occurs, in which there is an excessive growth of algae. The algae deplete the surrounding waters of oxygen, killing the marine life in it (Schindler, David, Vallentyne, Joh R, 2004).
As to the reason why guano is used to make fireworks, the answer is because nitrates are powerful oxidisers (Earl, 1978). Oxidisers are essential in explosives as it provides the oxygen needed to fuel the explosion (Earl, 1978). This is because as mentioned earlier nitrates are reduced fro nitrogen. As we have recently learnt, oxidizing agents are often the ones that had been reduced. Nitrates are often used as oxidisers because of the energy released from the triple bonds of nitrogen.
From my research on guano I realised how chemistry can be used to benefit and harm society. Using chemistry to isolate and mass produce nitrates in synthetic fertilsers from guano boosts agricultural production. However, these fertisers pollute the environment. Understanding the chemical properties of nitrates lead to the development of powerful explosives that can be used for peaceful purposes such as mining or harmful purposes such as terrorism. In conclusion, knowledge in chemistry can be used to benefit our lives and also identify potential threats.
Earl, Brian (1978), Cornish Explosives, Cornwall: The Trevithick Society
Schindler, David and Vallentyne, John R. (2004) Over fertilization of the World’s Freshwaters and Estuaries, University of Alberta Press