In the reaction with sodium, 4 grams of hydrogen were released. Calculate the mass of the entered water.

Reaction equation: 2Na + H2O = Na2O + H2
According to the periodic table, we determine the molar mass of hydrogen: M = 1 * 2 = 2 g / mol. And water M = 1 * 2 + 16 = 18 g / mol.
Let’s find the amount of released hydrogen: n = m / M = 4 g / 2 g / mol = 2 mol.
According to the reaction, 1 mol of hydrogen is obtained from 1 mol of water, which means n (H2O) = n (H2) = 2 mol.
Find the mass of water: m = n * M = 2 mol * 18 g / mol = 36 g.
Answer: the mass of water is 36 g.