Acetylene can be prepared from calcium carbonate by a series of reactions. The mass of 50% calcium carbonate required to prepare 2moles of acetylene is

CaCO3→CaO+CO2                CaO+3C→CaC2+2CO↑                CaC2+2H2O→C2H2+Ca(OH)2                1mole C2H2  obtained from →1mole  CaCO3                2mole C2H2  obtained from →?                      =2mole  CaCO3=200gm   CaCO3                 ∴  Mass of 50%  pure CaCO3  required =200×10050=400gm