Recording-2025-03-11T03_39_05.938Z

Overview of Electrochemistry

• Electrochemistry is considered one of the easier chapters.

• It is important to recall knowledge from previous chapters as topics blend together towards the end of the chapter.

• Most calculations can be done mentally without a calculator, except for specific cases.

Oxidation Numbers

• Oxidation numbers are equivalent to charges or valence electrons, commonly referred to as oxidation numbers in AP chemistry.

• The oxidation states of elements in compounds are crucial for determining oxidation and reduction processes.

Example Calculations

• For the compound AsO4^3-:

  • O: -2 (4 oxygens = -8 total)

  • To achieve a total charge of -3, As must be +5.

• For the compound HNO3 (charge of zero):

  • H: +1 (3 H = +3)

  • Therefore, N must be -3 to balance the charge (total = 0).

• For the compound BaCl204:

  • Ba: +2 (1 Ba)

  • Cl: use total oxygen contribution to find Cl's oxidation state (Cl must be +3).

Key Concepts in Electrochemistry

• Reduction vs. Oxidation:

  • Reduction: gain of electrons (decreases charge).

  • Oxidation: loss of electrons (increases charge).

  • Mnemonic: LEO the lion goes GER (Loss of Electrons is Oxidation, Gain of Electrons is Reduction).

Determining Redox Reactions

1. Cu^2+ to Cu:

   • Balance elements: 1 Cu on both sides.

   • Charge: Left (2+), Right (0).

   • Add 2 electrons to the left (Cu is reduced).

2. Cr^6+ to Cr^3+:

   • Balance elements: 1 Cr on both sides.

   • Charge: Left (6+), Right (3+).

   • Add 3 electrons to the left (Cr is reduced).

3. Cl^- to Cl2:

   • Start with balancing chlorines and charges to determine oxidation.

   • Add appropriate electrons to represent oxidation (Cl is oxidized).

Important Points to Remember

• Always choose the reactants when determining which species is oxidized or reduced.

• Electrons added to the left indicates reduction, while those added to the right indicates oxidation.

• In questions involving oxidation states, the focus is on reactants, not products.

Exam Preparation Tips

• Understand how to calculate oxidation numbers for various elements and compounds as these concepts commonly appear in FRQs.

• If you're unsure about oxidation numbers, remember they simply reflect the charge of an atom in a compound.

• Prepare for both theoretical questions and practical real-world applications involving oxidation and reduction reactions.

Conclusion

• If you have questions or need clarification on any concept, ask for help. Don't hesitate as you study this chapter.