AP Chemistry Multiple Choice Strategy and Sample Questions

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Strategy for AP Chemistry Test

• Goal: Understand traps in the AP Chemistry test and how to outsmart them for a better score.

Sample Question Analysis

Stoichiometry Without Calculators

• Question about the reaction of iron and sulfur to form iron (II) sulfide (FeS).
• The question tests understanding of stoichiometry without using calculators, implying it relies on simple math or conceptual understanding.
• Key Concept: Iron, having a higher molar mass than sulfur for the same given mass, implies it has fewer moles, thus being the limiting reagent.
• The complete reaction consumes all iron, leaving behind FeS and excess sulfur.

Bronsted-Lowry Acid-Base Pairs

• Definition: Bronsted-Lowry acid donates H+ (proton), and base accepts H+.
• Key Concept: Conjugate pairs differ by one H+.
• Correct Answer: H2PO4- ➔ HPO4 2- (differ by one proton)
• Common Mistakes Include:
  • Confusion with strong acids like nitric acid, which fully dissociates.
  • Incorrect pairings not adhering to the one H+ difference rule.

Photoelectron Spectroscopy (PES) Analysis

• PES graphs detail electron distribution over energy levels.
• Key Concept: Reading PES graphs helps identify elements or electron configurations.
• Correct Identification: Aluminum, from analyzing PES graph peaks and inferring electron configuration.

Solubility and Concentration

• Solving for the concentration of ammonium phosphate from given molarity of ammonium ions.
• Key Concept: Use given ratios and stoichiometry to find unknown concentrations.
• Correct Answer: 0.50 molar, based on a 1 to 3 ratio of ammonium phosphate to ammonium ion.

Titration Calculation

• Antacid tablet containing calcium hydroxide titrated with hydrochloric acid.
• Key Concept: Understanding the stoichiometry of titration and calculating based on given data (buret reading and molarity).
• Correct Answer: Find moles of HCl used, apply stoichiometric ratios to find moles and mass of calcium hydroxide in the tablet.

Ionization and Acidity in Oxyacids

• The effect of electronegativity and the number of oxygens on acid strength.
• Key Concept: More electronegative elements or more oxygen atoms increase acidity by weakening O-H bonds.

Spontaneity of Reactions

• Factors determining reaction spontaneity: enthalpy (ΔH) and entropy (ΔS).
• Key Concept: Exothermic reactions with increasing entropy are spontaneous.

Redox Titration Lab Procedure

• Proper preparation steps before starting a titration.
• Key Concept: Prevent error and ensure accurate molarity by rinsing the buret with the titrant solution, not just water.

Rate Laws from Initial Rate Data

• Using initial rate data to determine order of reaction with respect to reactants.
• Key Concept: Analyze changes in reactant concentrations and their effect on the reaction rate.

Changes to Reactions at Equilibrium

• Le Chatelier's principle in assessing the impact of changes on equilibrium.
• Key Concept: System will adjust to oppose the change applied to it.