Calcium carbide is not volatile and not soluble in any known solvent, and reacts with water to yield acetylene gas and calcium hydroxide. Its density is 2.22 g/cm3. Its melting point is °C, and its boiling point is °C. Since the acetylene that forms upon contact with water is flammable, the substance is listed in hazard class 4.3.
Calcium acetylide was first obtained by German chemist Friedrich Wohler in when he heated an alloy of zinc and calcium with coal. The scientist described the reaction of calcium carbide with water. Calcium carbide reacts vigorously with even mere traces of H2O, releasing a large amount of heat. If there is an insufficient quantity of water, the resulting acetylide spontaneously combusts. Calcium acetylide reacts violently with aqueous solutions of alkalis and diluted non-organic acids. These reactions release acetylide. With its strong reductive properties, CaCz reduces all metal oxides to pure metals or turns them into carbides.
It is easier to obtain calcium carbide from its oxide than from calcium itself, as the oxide is reduced at temperatures above °C. The metal and carbon combine:
CaO + 3C→CO↑+ CaCz
The reaction takes place in an electric arc furnace, where a mixture of unslaked lime and coke or anthracite is heated. The technical product is grey due to the presence of free carbon, calcium oxide, phosphide, sulfide, and other chemical compounds. CaC2 com-prises 80-85% of the product by mass.
For laboratory purposes, acetylene can be obtained from the hydrolysis of calcium car-bide. To avoid local overheating, it is recommended to use generators in which calcium carbide is immersed in a relatively large amount of water. The acetylene that is released in the reaction is contaminated by impurities of ammonia, oxygen and hydrogen sulfide (its main mass is absorbed by the water alkaline medium), hydrogen phosphide, silicon hydride and hydrogen arsenide. This reaction is interesting from a historical standpoint, for in the era of gas lamps, private houses and public buildings were lit with acetylene lamps. They were even installed in the first cars. Portable acetylene lamps are used in mines to this day. Nowadays, in the reaction of the hydrolysis of calcium carbide, much more acetylene is obtained than in the past, but acetylene is no longer the final product of synthesis. The substance is used as an intermediate product for the synthesis of or-ganic compounds. On the basis of the hydrolysis reaction of calcium carbide, several methods for determining water content have been developed. In the majority of them, the amount of acetylene is measured by manometric or volumetric methods. Other methods have found a limited use based on the combustion of acetylene, in which oxy-gen consumption or flame intensity is measured.
Calcium carbide affects the neurological system by inducing prolonged hypoxia. It is known to cause symptoms like headache, dizziness, high sleepiness, memory loss, cerebral oedema, numbness in the legs and hands, general weakness, cold and damp skin, low blood pressure and seizures.
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Prolonged exposure to calcium carbide may cause a build-up of fluid in the lungs (pulmonary edema), a medical emergency.
According to the latest research done by scientists, when calcium carbide comes in contact with moisture in the atmosphere, it produces acetylene gas, which like ethylene accelerates the ripening process of fruits and vegetables.
Calcium carbide is considered hazardous by the OSHA Hazard Communication Standard.
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