How many grams of magnesium is required when interacting with hydrochloric acid to obtain 160 grams of magnesium chloride?

Given:
m (MgCl2) = 160 g

To find:
m (Mg) -?

Decision:
1) Write the reaction equation:
Mg + 2HCl => MgCl2 + H2 ↑;
2) Calculate the molar masses of MgCl2 and Mg:
M (MgCl2) = Mr (MgCl2) = Ar (Mg) * N (Mg) + Ar (Cl) * N (Cl) = 24 * 1 + 35.5 * 2 = 95 g / mol;
M (Mg) = Mr (Mg) = Ar (Mg) = 24 g / mol;
3) Calculate the amount of MgCl2 substance:
n (MgCl2) = m (MgCl2) / M (MgCl2) = 160/95 = 1.7 mol;
4) Determine the amount of MgCl2 substance:
n (Mg) = n (MgCl2) = 1.7 mol;
5) Calculate the mass of Mg:
m (Mg) = n (Mg) * M (Mg) = 1.7 * 24 = 41 g.

Answer: The mass of Mg is 41 g.