How many grams of water can form if 113 g of acetylene is burned?

C2H2, or acetylene, has a molar mass of 26g. That means it has 113/26 = around 4.34 mols. Assuming complete combustion, the balanced equation comes out to this:

C2H2 + 3O2 - - > 2H2O + 2CO2

Using the molar ratios, we get that we get 8.68 mols of water for every 4.34 mols, so since the molar mass of water is 18 grams per mol, we multiply 18 * 8.68 = about 156.24 grams.