Oxygen: an element that caused an ecological catastrophe
Chemical properties and the most interesting facts about oxygen
Oxygen is the most abundant element on Earth. It comprises almost half of the mass of the earth’s crust and 86% of the mass of the ocean, and the Earth’s atmosphere contains around 21% oxygen by volume. In the universe, oxygen is the third-most abundant element after hydrogen and helium. Our planet stands out among the other planets of the Solar System by its high oxygen content. Oxygen forms the molecules of ozone O₃, and the ozone layer of our planet, which absorbs harsh ultraviolet radiation from space.
Gaseous, liquid and solid oxygen
In free form and in normal conditions, oxygen exists in the form of two gases: oxygen O₂ – a gas without color, taste or smell, and ozone O₃ – a blue gas with a specific smell which can be felt during a storm, for instance. In liquid form (at a temperature below –182.96 °C), oxygen has a bright blue color, while at –218.35 °C it forms bright indigo crystals. Liquid oxygen is paramagnetic, i.e. like iron it is attracted to a magnet!
How oxygen was discovered
The discovery of oxygen is shared among three chemists from different countries. Oxygen was first isolated by Joseph Priestley on the 1st of August 1774, when he heated mercury oxide in a hermetically sealed vessel using sunrays focused through a lens. But Priestley did not think he had discovered a new element. In 1777, the Swedish chemist Carl Scheele published a book where he described his experiments six years earlier to obtain “fiery air” (Scheele heated saltpeter with sulfuric acid, and then broke down the nitrogen oxide released). However, the French chemist Antoine Lavoisier, who was aware of the works both Priestley and Scheele, had the final say in the matter.
By conducting works on burning various substances and weighing the resulting oxides, Lavoisier showed that the weight of the oxides was greater than the initial elements, which meant that a certain substance from the air was attaching itself to them. Lavoisier finally established that the air contained a new element, and at the same time debunked the theory of phlogiston that was dominant at the time. Lavoisier called the new element “oxygene” – “forming acids”, as he thought that all acids contained oxygen.
Chemical properties of oxygen
Oxygen may be obtained in the laboratory, for example by the breakdown of hydrogen peroxide. The catalyst of this reaction is manganese (IV) oxide:
2H₂O₂ → 2H₂O + O₂↑
Oxygen is very reactive, and can directly (at certain temperatures, pressure or in the presence of a catalyst) react with all other elements, with the exception of gold and inert gases. It is a good oxidizer and supports combustion. If a smoldering stick is put in an atmosphere of oxygen, it will catch fire once more. Heated sulfur burns in an atmosphere of oxygen with a blue flame, and sulfur (IV) oxide forms:
S + O₂ → SO₂
Iron wool burns poorly in air, as it does not have a sufficient amount of oxygen, but if it is soaked in liquid oxygen, it burns rapidly with the formation of double iron (II, III) oxide:
3Fe + 2O₂ → Fe₃O₄
The oxidizing properties of oxygen can be seen in the experiment “Chemical traffic light”. If an alkaline solution of glucose and a blue solution of indigo carmine is mixed, the latter is oxidized by the oxygen dissolved in the liquid, and turns green. Over time, glucose reduces the indigo carmine, causing the solution to change color, first to red, and then to yellow. If the solution is shaken, a new portion of oxygen from the air dissolves in it, the indigo carmine is oxidized once more, and the solution turns green.
Where oxygen is used
It is used as an oxidizer in metallurgy in the manufacture of steel, and for the oxygen welding of metals. It is also essential in the manufacture of nitric acid, hydrogen peroxide, epoxyethane and other products of the chemical industry. Oxygen is used as rocket fuel together with hydrogen peroxide, nitric acid and other compounds rich in oxygen, as an oxidizer. A mixture of oxygen and ozone is also a good oxidizer.
Many processes of the chemical industry connected with oxidation require the presence of oxygen. In medicine, oxygen is used in breathing apparatuses, and also in the form of oxygen cocktails – to treat disorders of the digestive tract. In the food industry, oxygen is used as a propellent and packaging gas, and is indicated as food additive E948. In agriculture, oxygen cocktails are used to enrich the water environment of fishing farms, and in livestock breeding to make animals gain weight.
However, the most successful use of oxygen was found by nature itself – oxygen is one of the vitally important elements. Breathing processes take place thanks to oxygen. Oxygen makes it possible to gain and store energy in the form of ATP, and it is present in DNA. Most organic molecules, which are the foundation of life, contain oxygen. An oxygen deficit can cause tissue to die. Hypoxia brain (which can be caused by the consumption of alcohol and smoking) leads to the death of nerve cells.
In the biosphere, oxygen is produced by photosynthesis, and the majority of it is released by the phytoplankton of the world ocean.
Sources:
- Paul Parsons, Gail Dixon — The Periodic Table A visual guide to the elements (pp.26-29);
- RSC/Periodic element/Oxygen;
- Wikipedia/Oxygen;
- Wikipedia/Ozone;
- Wikipedia/Great Oxygenation Event.
