Stoichiometry—the heart of chemistry—can feel daunting at first, but with practice, it becomes second nature. This post provides a range of AP Chemistry stoichiometry practice problems, from basic mole conversions to more advanced scenarios involving limiting reactants and percent yield. Whether you're aiming for a 5 on the AP exam or simply solidifying your understanding, these problems will help you hone your skills.
Fundamental Stoichiometry Problems
Let's start with the basics: converting between grams, moles, and molecules using molar mass and Avogadro's number.
Problem 1: How many moles of carbon dioxide (CO₂) are present in 44.0 grams of CO₂? (Molar mass of CO₂ = 44.0 g/mol)
Problem 2: Calculate the mass in grams of 2.50 moles of water (H₂O). (Molar mass of H₂O = 18.0 g/mol)
Problem 3: Determine the number of molecules in 10.0 grams of methane (CH₄). (Molar mass of CH₄ = 16.0 g/mol; Avogadro's number = 6.022 x 10²³ molecules/mol)
Mole Ratio Problems and Balanced Equations
This section focuses on using balanced chemical equations to determine mole ratios and solve stoichiometric problems. Remember, the coefficients in a balanced equation dictate the mole ratios of reactants and products.
Problem 4: Consider the reaction: 2H₂ + O₂ → 2H₂O. If you have 4.0 moles of hydrogen gas (H₂), how many moles of water (H₂O) can be produced?
Problem 5: For the reaction: N₂ + 3H₂ → 2NH₃, calculate the mass of ammonia (NH₃) produced from 10.0 grams of nitrogen gas (N₂). (Molar mass of N₂ = 28.0 g/mol; Molar mass of NH₃ = 17.0 g/mol)
Problem 6: The combustion of propane (C₃H₈) is represented by the equation: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. If 50.0 grams of propane react completely, how many grams of carbon dioxide (CO₂) are formed? (Molar mass of C₃H₈ = 44.0 g/mol; Molar mass of CO₂ = 44.0 g/mol)
Limiting Reactants and Percent Yield
These problems introduce the concepts of limiting reactants and percent yield, pushing your stoichiometric skills to the next level.
Problem 7: Consider the reaction: Fe₂O₃ + 3CO → 2Fe + 3CO₂. If 10.0 grams of Fe₂O₃ react with 10.0 grams of CO, which is the limiting reactant? How many grams of iron (Fe) are produced? (Molar mass of Fe₂O₃ = 159.7 g/mol; Molar mass of CO = 28.0 g/mol; Molar mass of Fe = 55.8 g/mol)
Problem 8: In a reaction producing silver chloride (AgCl) from silver nitrate (AgNO₃) and sodium chloride (NaCl), the theoretical yield of AgCl is calculated to be 15.0 grams. If the actual yield obtained is 12.0 grams, what is the percent yield of the reaction?
Advanced Stoichiometry: Solution Stoichiometry
This section explores problems involving molarity and solution concentrations.
Problem 9: What volume of 0.50 M HCl solution is needed to completely react with 25.0 mL of 1.0 M NaOH solution? (The balanced equation is HCl + NaOH → NaCl + H₂O)
Problem 10: A 25.0 mL sample of a sulfuric acid (H₂SO₄) solution is titrated with 0.100 M NaOH solution. If 30.0 mL of NaOH are required to reach the endpoint, what is the concentration of the H₂SO₄ solution? (The balanced equation is H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O)
These practice problems offer a solid foundation for mastering stoichiometry in AP Chemistry. Remember to practice regularly, focusing on understanding the underlying concepts rather than just memorizing formulas. Good luck!
