Question

How is acetylene prepared in the laboratory?

Answer 1

Acetylene is prepared by the reaction of water and calcium carbide.

In a conical flask with a dropping funnel and delivery tube, calcium carbide lumps are placed on top of the layer of sand. Ethyne (acetylene) ($C_2{H}_4$) is formed when water is poured from the dropping funnel. It is passed through the acidified solution of Copper sulphate ($CuS{O}_4$) for purification.

The Acetylene gas ($C_2{H}_4$) prepared by the above method contains impurities of $H_{2}S,P{H}_3,N{H}_3,As{H}_3,$ (Hydrogen sulphide, Phosphene, Ammonia, Arsene) etc. due to the contaminations of calcium carbide. Therefore, the gas is passed through an acidified solution of CuSO₄ which removes the impurities as follows:

$\underset{\mathrm{Copper}\mathrm{sulphate}}{{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydrogen}\mathrm{sulphide}}{{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)}\to \underset{\mathrm{Copper}\mathrm{sulphide}}{\mathrm{CuS}\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}$

$\underset{\mathrm{Copper}\mathrm{sulphate}}{3{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Phosphene}}{2{\mathrm{PH}}_3\left(\mathrm{g}\right)}\to \underset{\mathrm{Copper}\mathrm{phosphide}}{{\mathrm{Cu}}_3{\mathrm{P}}_2\left(\mathrm{s}\right)}+3\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}$

$\underset{\mathrm{Ammonia}}{2{\mathrm{NH}}_3\left(\mathrm{l}\right)}+\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Ammonium}\mathrm{sulphate}}{{\left({\mathrm{NH}}_4\right)}_2{\mathrm{SO}}_4\left(\mathrm{s}\right)}$

$\underset{\mathrm{Copper}\mathrm{sulphate}}{3{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Arsene}}{2{\mathrm{AsH}}_3\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Copper}}{3\mathrm{Cu}\left(\mathrm{s}\right)}+\underset{\mathrm{Arsenous}\mathrm{acid}}{3{\mathrm{H}}_3{\mathrm{AsO}}_3\left(\mathrm{aq}\right)+}3\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}$

The pure gas is then collected by downward displacement of water.