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.