Calcium oxide (CaO) is an inorganic compound containing calcium and oxygen in ionic forms (not to be confused with calcium peroxide, CaO) 2 ). It is known throughout the world as lime, a term that designates any inorganic compound that contains carbonates, calcium oxides, and hydroxides, as well as other metals such as silicon, aluminum, and iron.
This oxide (or lime) is also colloquially called quicklime or slaked lime, depending on whether it is hydrated or not. Lime is calcium oxide, while slaked lime is its hydroxide. In contrast, limestone (limestone or hard lime) is actually a sedimentary rock composed primarily of calcium carbonate (CaCO 3 ).
It is one of the largest natural sources of calcium and constitutes the raw material for the production of calcium oxide. How is this oxide produced? Carbonates are highly susceptible to thermal decomposition; Heating calcium carbonate at temperatures above 825 °C leads to lime and carbon dioxide formation.
The above statement can be described as follows: CaCO 3 (S) → CaO (S) + CO 2 (G). Because the Earth’s crust is rich in limestone and calcite, and oceans and sea coasts contain abundant sea shells (the raw material for the production of calcium oxide), calcium oxide is a relatively cheap reagent.
Formula
The chemical formula of calcium oxide is CaO, with calcium as the acid ion (electron acceptor) Ca 2+ , and oxygen as the basic ion (electron donor) OR 2– .
Why does calcium have a +2 charge? Because calcium belongs to group 2 of the periodic table (Mr Becambra), and has only two valence electrons available for bond formation, which yields the oxygen atom.
structure
In the upper image, the crystalline structure (gem-salt type) for calcium oxide is represented. The red circles correspond to ions 2+ and the white ones extend to ions 2- .
In this cubic crystal, each ion is arranged as 2+ surrounded by six ions O 2- , placed between them in the holes of the octahedron left by the larger ions.
This structure expresses the maximum ionic character of this oxide, although the notable difference of radii (the red sphere is larger than the white one) gives it a weaker crystalline lattice energy than that of MgO.
Property
Physically, it is a crystalline white solid, odorless and with strong electrostatic interactions, which are responsible for its high melting point (2572 °C) and boiling (2850 °C). Furthermore, it has a molecular weight of 55,958 g/mol and the interesting property of being thermoluminescent.
This means that a piece of calcium oxide exposed to a flame can glow with an intense white light, known in English as pyroglobe , or in Spanish, light of calcium. The Ca ions 2+ , when exposed to fire, they cause a red colored flame, as shown in the following image.
solubility
CaO is a basic oxide that has a strong affinity for water, to the extent that it absorbs moisture (it is a hygroscopic solid), reacting immediately to produce slaked lime or calcium hydroxide:
CaO (s) + H 2 O (l) => Ca (OH) 2 (s)
This reaction is exothermic (releases heat) due to the formation of a solid with stronger cations and a more stable crystal lattice. However, the reaction is reversible when Ca(OH) 2 is heated , dehydrating it and igniting slaked lime; Then, Lime “Reborn”.
The resulting solution is very basic, and if it is saturated with calcium oxide it reaches a pH of 12.8.
Likewise, it is soluble in glycerol and in acid and sugar solutions. As it is a basic oxide, it naturally has effective interactions with acid oxides (SiO 2 , Co 2 O 3 and BeSh 2 O 3 , for example) due to being soluble in liquid phases. On the other hand, it is insoluble in alcohol and organic solvents.
applications
CaO has a great number of industrial uses, as well as in the synthesis of acetylene (CHCHCH), in the extraction of phosphates from waste water and in reaction with sulfur dioxide from gaseous wastes.
Other uses of calcium oxide are described below:
as a mortar
If calcium oxide is mixed with sand (SiO 2 ) and water, the sand cakes and slowly reacts with water to form slaked lime. In turn, C.O. 2 air dissolves in water and reacts with the salt to form calcium carbonate:
Ca (OH) 2 (s) + CO 2 (g) => CaCO 3 (s) + H 2 O (l)
The CaCO 3 It is a more resistant and hard compound than CaO, allowing the mortar (the previous mixture) to harden and fix the bricks, blocks or ceramics between them or on the desired surface.
in the production of glasses
The raw materials required for the production of glasses are silicon oxide, which, mixed with lime, sodium carbonate (Na 2 CO 3 ) and other additives, may then be subjected to heating, resulting in a shiny solid. This solid is later heated and blown into any figure.
in mining
Slaked lime is more abundant than quicklime due to hydrogen bonding (OHO) interactions. This property is used to break rocks from within.
This is achieved by filling them with a compacted mixture of lime and water, which is sealed in the rock to concentrate its heat and dissipative power.
as a silicate remover
CaO is combined with silicates to form a silicate liquid, which is then extracted from the raw material of a certain product.
For example, iron ore is the raw material for the production of metals and iron. These minerals contain silicates, which are undesirable impurities for the process and are eliminated only by the method described.
Calcium Oxide Nanoparticles
Calcium oxide can be synthesized as nanoparticles, allowing varying concentrations of calcium nitrate (Ca (NO) 3 ) 2 ) and sodium hydroxide (NaOH) in solution.
These particles are spherical, basic (as well as macro-scale solids) and have a lot of surface area. Consequently, these properties benefit catalytic processes. What? The investigation is currently answering that question.
These nanoparticles have been used to synthesize organic compounds—as derived from pyridines—for the purification of water from heavy metals and in the manufacture of new drugs to perform chemical transformations such as artificial photosynthesis, and photocatalytic agents. .
Nanoparticles can be synthesized on an organic support, such as papaya and green tea leaves, for use as an antibacterial agent.
