Consider the reaction of magnesium metal with hydrochloric acid to produce magnesium chloride and hydrogen gas. if 3.56 mol of magnesium and 3.56 mol of hydrochloric acid are reacted, how many grams of excess reactant are left over?

43.27 g Mg

The balanced equation for the reaction between magnesium metal and hydrochloric acid is;

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

From the equation;

1 mole of magnesium reacts with 2 moles of HCl

We are given;

3.56 moles of Mg and 3.56 moles of HCl

Using the mole ratio;

3.56 moles of Mg would react with 7.12 moles of HCl, and

3.56 moles of HCl would react with 1.78 moles of Mg

Therefore;

The amount of magnesium was in excess;

Moles of Mg left = 3.56 moles - 1.78 moles

                         = 1.78 moles

But; 1 mole of Mg = 24.305 g/mol

Therefore;

Mass of magnesium left = 1.78 moles × 24.305 g/mol

                                        = 43.2629 g

                                        = 43.27 g

Thus, the mass of magnesium that remained after the reaction is 43.27 g

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