Step four Calculate the mass of reactant needed using the moles calculated in step 3 and the gram formula mass of the reactant.

There are only 0.25 moles of HCl (instead of 0.3 moles), so the HCl will run out first. It is the limiting reactant. Now use the moles of the limiting reactant to calculate the mass of the product.

S115: Stoichiometry – Limiting Reagents : Mg + HCl Introduction Magnesium metal is dissolved in HCl in 500mL Florence flasks covered with balloons. The moles of each reagent are changed in each flask ...