Hydrolysis of calcium carbide and characteristics of the substance
How calcium acetylide reacts with water
Carbides are formed in the interaction of carbon with metals, at high temperatures. Calcium carbide is the most important of all carbides, and pure CaC₂ is a solid substance that crystallizes well. Its colorless crystals are formed by the ions Ca²⁺ and C₂²⁻. This substance is also known as calcium acetylide.
The history of obtaining the compound and its physical properties
Calcium carbide has become widely used in modern industry. The molecule of the substance was first synthesized in 1862 by the German chemist Friedrich Wöhler.
The scientist obtained calcium carbide by the following method: he prepared a compound of calcium and zinc, then heated it with coal. As a result of the reaction, carbide formed. The chemical formula of the compound is CaC₂. The industrial method of obtaining carbide was discovered in 1892 by the scientist Moissan.
By its physical properties, calcium carbide is a crystalline substance with a melting temperature of 2300 degrees Celsius. This figure is applicable exclusively for the pure compound. For carbide containing impurities, other melting temperatures apply. The main aggregate state of the substance is solid, and the color of carbide varies from grey to brown.
Chemical properties and methods of obtaining the substance
Calcium carbide absorbs water well — this process is accompanied by a breakdown reaction. Carbide dust has an irritant effect on the skin, the mucous membranes and respiratory organs. So when working with the compound, you must use dust or gas masks. Calcium carbide interacts with oxygen at a high temperature, with calcium carbonate forming in this reaction. In a reaction with nitrogen, a synthesis of calcium cyanamide forms. At high temperatures, calcium carbide enters into a reaction with phosphorous, chlorine and arsenic. One of the most important properties of the substance is the breakdown by water.
Calcium carbide is manufactured as follows: pulverized coke and unslaked lime are mixed. The resulting mixture is placed in electric furnaces and melted. Equal masses of calcium oxide and coke are taken. The process takes place at a temperature of 1900 degrees Celsius. The compound comes out of the furnace and is poured into special molds. The hardened calcium carbide is broken up and sorted by the size of the pieces. Granules of the substance are divided into four groups according to their sizes: 25×80, 15×25, 8×15, 2×8.
By its composition, technical calcium carbide contains 75-80% of the original substance. Impurities such as lime, carbon and others account for up to 25% of the total mass. Calcium sulfide and phosphide contained in technical carbide create a very unpleasant smell. The reaction for obtaining СаС₂:
СаО + 3С → СаС₂ + СО↑
The formation of calcium acetylide is accompanied by an absorption of heat, and so the reaction of its breakdown takes place with the release of energy.
Hydrolysis reaction of calcium carbide
Carbide can be regarded as calcium acetylide, i.e. as a calcium derivative of acetylide, or an acetylide salt. Like every salt formed by a strong base and a weak acid, calcium carbide is hydrolyzed by water. The reaction of calcium carbide with water takes place violently, with release of heat – slaked lime and acetylene form. We also recommend you to read a more detailed description of a reaction between carbide and water.
For laboratory purposes, acetylene can be obtained from the hydrolysis of calcium carbide. 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 organic 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 oxygen consumption or flame intensity is measured.
The use of calcium carbide
Calcium carbide is used in various spheres of life, above all in industrial synthesis. Calcium carbide is required for the manufacture of acetic acid, synthetic rubber, ethylene, acetone, styrene and vinyl chloride. Calcium carbide is valuable for its use in the synthesis of cyanide substances and fertilizers. The substance is used in agriculture – a carbide-carbamide regulator is used for regulating plant growth. This compound is also used in the process of manufacturing calcium cyanamide – the reaction is based on heating calcium carbide with nitrogen. Calcium carbide is also used in the reduction of alkaline metals, and in gas welding.