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Oxygen gas is increasingly obtained by these non-cryogenic technologies (see also the related vacuum swing adsorption). [103] Oxygen gas can also be produced through electrolysis of water into molecular oxygen and hydrogen. DC electricity must be used: if AC is used, the gases in each limb consist of hydrogen and oxygen in the explosive ratio 2:1.
Nine of the 23 nonmetallic elements are gases, or form compounds that are gases, and are extracted from natural gas or liquid air. These elements include hydrogen, helium, nitrogen, oxygen, neon, sulfur, argon, krypton, and xenon. For example, nitrogen and oxygen are extracted from air through fractional distillation of liquid air.
Oxygen is a strong oxidising agent (O 2 + 4e → 2H 2 O = 1.23 V at pH 0). Metal oxides are largely ionic in nature. [7] Sulfur. Sulfur is a bright-yellow moderately reactive [8] solid. It has a density of 2.07 g/cm 3 and is soft (MH 2.0) and brittle. It melts to a light yellow liquid 95.3 °C and boils at 444.6 °C.
From left to right in the periodic table, the nonmetals can be divided into the reactive nonmetals and the noble gases. The reactive nonmetals near the metalloids show some incipient metallic character, such as the metallic appearance of graphite, black phosphorus, selenium and iodine. The noble gases are almost completely inert.
Oxygen, sulfur, and selenium are nonmetals, and tellurium is a metalloid, meaning that its chemical properties are between those of a metal and those of a nonmetal. [7] It is not certain whether polonium is a metal or a metalloid. Some sources refer to polonium as a metalloid, [2] [27] although it has some metallic properties.
It uses a liquid iron cathode, an anode formed from an alloy of chromium, aluminium and iron, [123] and the electrolyte is a mixture of molten metal oxides into which iron ore is dissolved. The current keeps the electrolyte molten and reduces the iron oxide. Oxygen gas is produced in addition to liquid iron.
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Solid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K (−218.79 °C, −361.82 °F). Solid oxygen O 2 , like liquid oxygen , is a clear substance with a light sky-blue color caused by absorption in the red part of the visible light spectrum.