How do you figure out moles?

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.