When magnesium metal and an aqueous solution of hydrochloric acid combine, they produce an aqueous solution of magnesium chloride and hydrogen gas. Using the equation, Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g), if 48.6 g of Mg and 150.0 g of HCl are allowed to react, identify the limiting reagent
It takes 2 moles of HCl to react with each mole of Mg.
48.6 g of Mg = ? moles
150.0 g of HCl = ? moles
If there are less than half as many moles of Mg as HCl, it will be the limiting reagent.
To identify the limiting reagent, we need to determine which reactant (Mg or HCl) will be completely consumed first, thus limiting the amount of product that can be formed.
Step 1: Convert the masses of Mg and HCl to moles.
- Molar mass of Mg = 24.31 g/mol
- Molar mass of HCl = 36.46 g/mol
Number of moles of Mg = 48.6 g / 24.31 g/mol = 2 moles of Mg (approx.)
Number of moles of HCl = 150.0 g / 36.46 g/mol = 4.11 moles of HCl (approx.)
Step 2: Use the balanced equation to determine the stoichiometric ratio of Mg and HCl.
From the balanced equation: Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
- 1 mole of Mg reacts with 2 moles of HCl
Step 3: Compare the number of moles of each reactant to the stoichiometric ratio.
Number of moles of HCl (4.11) is greater than the stoichiometric ratio with Mg (2.00). Therefore, Mg is the limiting reagent.
Conclusion: Magnesium (Mg) is the limiting reagent as it will be completely consumed first.