text: The balanced reaction is:\nCaC2 + 2H2O ---> C2H2 + Ca(OH)2\n\nThe molar mass of CaC2 is 64 g/mol so you are starting with 0.5 moles of calcium carbide.  Since water reactions with CaC2 is a 1:2 ratio, you will need twice as much water, or 1.0 moles of water = 18 grams of water.