AP Chemistry Cram Session

Introduction

• Presented by Jeremy Kug.
• Final review session before the AP Chemistry exam.
• Accompany with guided notes PDF.
• Comprehensive resources available at ultimatereviewpacket.com.

Unit 1: Mass Percent and Mass Spectrometry

Mass Percent

• Calculate mass percent using atomic masses.
• Example 1: Magnesium chloride (MgCl₂)
  • Magnesium: 24.31 amu
  • Chlorine: 35.45 amu each (×2 = 70.90 amu)
  • Total: 95.21 amu
  • Mg mass percent: (24.31 / 95.21) × 100 ≈ 25.53%
  • Cl mass percent: (70.90 / 95.21) × 100 ≈ 74.47%
• Example 2: Calcium chloride (CaCl₂)
  • Calcium: 40.08 amu
  • Cl remains same
  • Total: 110.98 amu
  • Ca mass percent: (40.08 / 110.98) × 100 ≈ 36.11%
  • Cl mass percent: (70.90 / 110.98) × 100 ≈ 63.89%

Mass Spectrometry

• Mass Spectra: Graph depicting isotopes and abundance.
• Example: Element with isotopes at 85 amu (75%) and 87 amu (25%).
• Calculate average atomic mass.
• Compare to periodic table to identify element (e.g., Rubidium).

Electron Configurations

• Essential for writing electron configurations.
• Examples:
  • Chlorine: 1s² 2s² 2p⁶ 3s² 3p⁵
  • Chloride ion (Cl⁻): 3p⁶
  • Aluminum: 1s² 2s² 2p⁶ 3s² 3p¹
  • Aluminum ion (Al³⁺): Ends with 2p⁶

Periodic Table Trends

• Atomic Radius: Largest at bottom-left (e.g., Cesium).
• Ionic Radius: Cations smaller than anions.
• Ionization Energy: Highest on top-right (e.g., Helium).

Photoelectron Spectroscopy

• Analyze sublevels via peak heights.
• Determine electron configurations from graphs.

Unit 2: Lewis Structures and VSEPR

Lewis Electron Dot Structures

• Start with central atom; use valence electrons.
• Examples:
  • SF₂, CO₂

Bonding and Hybridization

• Sigma and pi bonds.
• Hybridization based on electron domains (e.g., sp³, sp²).

Molecular Geometry and Bond Angles

• Determine geometry via VSEPR.
  • Bent, Trigonal Planar, Tetrahedral.
• Bond angles: 104.5°, 120°, 109.5°

Polarity

• Dipole moments: Presence of unbalanced negative charge region.
• Intermolecular forces: London dispersion, dipole-dipole, hydrogen bonding.

Unit 3: Gas Laws and Spectrophotometry

Ideal Gas Law (PV=nRT)

• Use to find moles of gas mixture; calculate molar mass.

Spectrophotometry

• Use Beer-Lambert law for concentration analysis.
• Outliers indicate contamination.

Unit 4: Stoichiometry and Net Ionic Equations

Net Ionic Equations

• Identify spectator ions.
• Example: Mg with Cu²⁺ (CuCl₂)

Stoichiometry

• Convert to moles ➜ Use mole ratio ➜ Convert to final unit.
• Example: Reaction of Ag₂CO₃ and carbonate ions.

Unit 5: Kinetics and Rate Laws

Rate Laws

• Determine order by observing concentration changes and rate changes.
• Write rate laws from experimental data.

Graphical Method for Determining Order

• Plot concentration, ln(concentration), and 1/concentration vs. time.
• Identify order by which graph is linear.

Unit 6: Thermochemistry

Specific Heat Capacity

• Use Q=mcΔT to calculate heat exchange.
• Example problem with copper and water.

Heating Curves

• Temperature remains constant during phase changes (melting, boiling).

Enthalpy (ΔH)

• Calculate using formation enthalpies: Products minus reactants.

Unit 7: Equilibrium

Equilibrium Constant Expressions

• Write as products over reactants; omit solids/liquids.

ICE Tables

• Use for initial, change, equilibrium calculations.

Le Chatelier’s Principle

• Predict shifts due to concentration, pressure, temperature changes.

Unit 8: Acids and Bases

pH and pOH

• Relationship: pH + pOH = 14
• Calculate using hydronium and hydroxide concentrations.

Strong vs. Weak Acids/Bases

• Recognize common strong acids/bases.
• Use Ka, Kb for weak acid/base equilibrium calculations.

Titrations

• Use titration curves to find equivalence and half-equivalence points.
• Estimate acid/base concentrations from titration data.

Unit 9: Thermodynamics and Electrochemistry

Entropy (ΔS)

• Measure of dispersal of energy/matter.
• Predict signs for reactions based on states, number of molecules.

Gibbs Free Energy (ΔG)

• Calculate: ΔG = ΔH - TΔS
• Positive ΔG = non-favorable; Negative ΔG = favorable

Electrochemistry

• Galvanic Cells: Voltaic cells producing voltage from spontaneous reactions.
• Determine cell potential (E° cell), identify anode/cathode.

Conclusion

• Reminder to use guided notes.
• Encouragement for the exam; focus on understanding and applying concepts.