Question

Write the equation for the preparation ethyne from calcium carbide.

Answer 1

Calcium carbide has another name called calcium acetylide. In reaction with water molecules, it produces calcium hydroxide, also known as lime and ethyne gas. It is also manufactured by partial combustion of methane.

Complete step by step answer:
Calcium carbide $(Ca{C_2})$ is a chemical compound consisting of calcium and carbon atoms. It is a white crystalline substance when in pure form. It is obtained from the reaction when calcium reacts with carbon.
When calcium carbide $(Ca{C_2})$ reacts with water, ethyne gas is released. Ethyne is an industrial substance having an unpleasant odour, which is caused due to the presence of impurities it contains (ammonia, hydrogen sulphide, phosphine and others). In its pure form, ethyne $({C_2}{H_2})$ is a colourless gas with a characteristic faint-like smell, and it readily dissolves in water.
$Ca{C_2} + {H_2}O \to Ca{(OH)_2} + {C_2}{H_2}$
The acidic hydrogen attached to the carbon-carbon triple bond in the ethyne molecule, can separate from the rest of the molecule as a hydrogen ion, leaving the electro-negative carbon retaining both electrons from the broken covalent bond. Ethyne can thus react and bond with metals, which distinguishes it from alkenes.
Additional information: Ethyne $({C_2}{H_2})$ can also be manufactured by another method that involves the partial combustion of methane with oxygen, or by the cracking of hydrocarbons. Ethyne forms explosive mixtures reacting with air. Solid calcium carbide reacts with moisture in the air and produces gas. This builds up pressure in sealed containers containing the solid. That is why, care must be taken while opening them.

Note:
Ethyne is also termed as acetylene. It is a hydrocarbon and the simplest alkyne having triple bond between two carbons. It is used for welding and cutting and thus known as oxy-cutting or gas-cutting. It is typically a colourless gas.