Principle:

Ethyne gas(Acetylene) is prepared in the laboratory by the action of water on calcium carbide.

CaC₂ +  2H₂O  ----------> C₂H₂ + Ca(OH)₂   

Procedure:

Lumps of calcium carbide are placed on the layer of sand in conical flask fitted with a dropping funnel and delivery tube. Water is dropped from the dropping funnel whereby ethyne(acetylene)   is formed. It is passed through the acidified solution of CuSO₄ for the purification.

Figure: Laboratory preparation of Ethyne(Acetylene) gas

Purification :

The  ethyne gas prepared by the above method contains impurities of H₂S, PH₃, NH₃, AsH₃  etc. due to the contaminations of calcium carbide. Therefore,  the gas is passed through acidified solution of  CuSO₄ which remove the impurities as follows:

CuSO₄  +  H₂S  ----------> CuS  +H₂SO₄ 

3CuSO₄  +  2PH₃ ----------> Cu₃P₂   +  3H₂SO₄ 

2NH₃  +  H₂SO₄ ---------->  (NH₄)₂SO₄  

                                            3CuSO₄  +  AsH₃  +  3H₂O ---------->  3 Cu  +  H₃AsO₃ + 3H₂SO₄                                                     

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