AP Chemistry 2025 Free-Response Questions

General Information

• Duration: 1 hour 45 minutes
• Materials Allowed: Scratch paper, calculator (four-function, scientific, or graphing), periodic table, and reference materials.
• Instructions:
  • Show work clearly for calculations, including methods and steps.
  • Label answers clearly with part numbers (e.g., A, B, C).
  • Use significant figures appropriately.
  • Use a pencil or a pen with black or dark blue ink.
  • Optional pacing recommendations: 23 minutes for long questions (1-3) and 9 minutes for short questions (4-7).

Question 1: Magnesium

• Part A:
  • Complete a mass spectrum for magnesium isotopes.
  • Discuss differences in atomic structure between Mg-25 and Mg-26.
• Part B:
  • Explain using Coulomb’s law why Mg²⁺ has stronger attraction to water than Na⁺.
• Part C:
  • Calculate the pH of a NaOH solution.
• Part D:
  • Calculate the concentration of Mg²⁺ after mixing solutions without reaction.
• Part E:
  • Write Ksp expression for Mg(OH)₂.
  • Use reaction quotient Q to predict precipitate formation.
• Part F:
  • Discuss the effect of adding HNO₃ on the amount of undissolved Mg(OH)₂.

Question 2: Ascorbic Acid

• Part A:
  • Calculate moles of H₂O from combustion.
  • Determine empirical formula of ascorbic acid.
• Part B:
  • Calculate molarity of ascorbic acid in a titration.
  • Determine pKa and ratio of forms at pH 4.7.
• Part C:
  • Analyze a reaction rate with triiodide ion to determine order and rate constant.
• Part D:
  • Discuss intermolecular forces affecting triiodide ion solubility.

Question 3: White Phosphorus

• Part A:
  • Complete Lewis diagram for P₄.
• Part B:
  • Discuss entropy and enthalpy changes in P₄ reaction with oxygen.
• Part C:
  • Calorimetry experiment to find enthalpy change when P₄O₁₀ reacts with water.
• Part D:
  • Predict temperature changes in trials with incomplete reactant transfer.
• Part E:
  • Calculate standard enthalpy for formation of PCl₅.
• Part F:
  • Analyze equilibrium constant changes with temperature.

Question 4: Methanol and Formaldehyde

• Part A:
  • Identify hybridization in H₂CO.
• Part B:
  • Draw a hydrogen bond between CH₃OH and H₂CO.
• Part C:
  • Propose cooling temperature for liquid state.
  • Calculate thermal energy removal to condense methanol.

Question 5: Compounds X and Y

• Part A:
  • Predict geometry around Si in compound Y using VSEPR theory.
• Part B:
  • Discuss boiling point difference due to London dispersion forces.
• Part C:
  • Determine vapor pressure at boiling point of compound X.
• Part D:
  • Calculate moles of gas at high temperature and pressure.

Question 6: Galvanic Cell

• Part A:
  • Write oxidation half-reaction for Zn and Al galvanic cell.
• Part B:
  • Write balanced net ionic equation.
• Part C:
  • Determine which electrode mass changes more.
• Part D:
  • Find maximum voltage available with other half-cells.

Question 7: Glycolate Ion

• Part A:
  • Identify proton-accepting atom in glycolate ion.
• Part B:
  • Calculate Kb and Ka for glycolic acid.
• Part C:
  • Evaluate whether H₃O⁺ is a catalyst in a reaction mechanism.

End of Exam