1. mass = moles x molar mass Write the equation: m (in grams) = n x M. Extract the data from the question: n = 0.25 mol. Calculate the molar mass of the substance using the periodic table: M(H2O) = (2 x 1.008) + 16.00 = 18.016 g mol-1 Substitute the values into the equation and solve: mass = 0.25 x 18.016 = 4.504 g.
