How many grams of water are made from the reaction of 16.0 grams of oxygen gas?

Assuming hydrogen gas is in excess, calculate the moles of oxygen

n (O2) = 16.0 g / 32.0 g/mol = 0.500 mol

Calculate the moles of water using the mole ratio; the ratio of H2O to O2 is 2:1 or the moles of H2O is twice the moles of O2

n (H2O) = 2 x n (O2) = (2) (0.500) = 1.00 mol

Calculate the mass of H2O by multiplying the moles by the molar mass of water

mass = (1.00 mol) (18.0 g/mol) = 18.0 g H2O

Ans: A)