A mixture of calcium and calcium oxide weighing 5 g was treated with water. As a result of the reaction, 1.68 liters

A mixture of calcium and calcium oxide weighing 5 g was treated with water. As a result of the reaction, 1.68 liters of gas were released. Determine the mass fraction of calcium oxide in the initial mixture.

Let’s find the amount of substance H2.

n = V: Vn

n = 1.68 L: 22.4 L / mol = 0.075 mol.

Ca + 2 H2O = Ca (OH) 2 + H2 ↑.

n (H2) = n (Ca) = 0.075 mol.

Let’s find the mass of Ca.

M (Ca) = 40 g / mol.

m = nM.

m = 0.075 mol × 40 g / mol = 3 g.

Let’s find the mass of CaO in the mixture.

5 – 3 = 2 g.

Let’s find the mass fraction of CaO in the mixture.

5 g – 100%,

2 – x%.

x = (2 × 100%): 5 g = 40%.

Answer: 40%.