How much magnesium must be taken to react with hydrochloric acid to obtain 2.8 liters of oxygen?

Let’s find the amount of the substance hydrogen.

n = V: Vn.

n = 2.8 L: 22.4 L / mol = 0.125 mol.

Let’s compose the reaction equation, find the quantitative ratios of substances.

Mg + 2HCl = MgCl2 + H2.

According to the reaction equation, there is 1 mole of Mg per 1 mole of H2. Substances are in quantitative ratios 1: 1.

The amount of oxygen O2 is 2 times less than the amount of H2.

n (H2) = n (Mg) = 0.125 mol.

Let’s find the mass Mg.

M (Mg) = 24 g / mol.

m = n × M.

m = 24 g / mol × 0.125 mol = 3 g.

Answer: 3 y.