Calculate the mass of the salt obtained by reacting 20 g of magnesium with hydrochloric acid.

Let’s find the amount of magnesium substance.

n = m: M.

M (Mg) = 24 g / mol.

n = 20 g: 24 g / mol = 0.83 mol.

Let’s compose the reaction equation:

Mg + 2HCl = MgCl2 + H2 ↑.

According to the reaction equation, 1 mol of magnesium accounts for 1 mol of magnesium chloride, that is, the substances are in quantitative ratios of 1: 1, which means their amount of substances will be the same.

n (Mg) = n (MgCl2) = 0.83 mol.

Let’s find the mass of magnesium chloride.

m = n × M.

M (MgCl2) = 24 + 70 = 94 g / mol.

m = 94 g / mol × 0.83 mol = 78.02 g.

Answer: 78.02 g.