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Questions and Answers
What branch of chemistry deals with the relationships between electricity and chemical reactions?
In a neutral compound, all oxidation numbers must add up to one.
False
What is the oxidation state of free elements?
0
What is the oxidation state of fluorine?
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Which of the following represents an oxidizing agent?
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In oxidation, electrons are ______ and in reduction, electrons are ______.
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Match the following processes with their appropriate terms:
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What mnemonic device can help remember oxidation and reduction?
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In the half reaction Fe + Cu2+ → Cu + Fe2+, what is the oxidation process?
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What are the products of the half-reaction Cu + HNO3 → Cu(NO3)2 + NO + H2O?
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Study Notes
Electrochemistry Overview
- Electrochemistry studies the interplay between electricity and chemical reactions.
- It encompasses both spontaneous and nonspontaneous processes.
- In redox reactions, energy released from spontaneous reactions is converted to electricity, while electrical energy can induce nonspontaneous reactions.
Oxidation States
- The sum of oxidation numbers in a neutral compound equals zero.
- In ions, the sum matches the ion's charge.
- Free elements have an oxidation number of zero (e.g., Na, Fe, H₂, O₂).
- Key oxidation rules include:
- Fluorine: -1
- Group 1 metals: +1, Group 2 metals: +2
- Hydrogen: +1 with non-metals, -1 with metals
- Oxygen: -2 (with exceptions for fluorine and peroxides)
- Group 17 (7A): -1, Group 16 (6A): -2, Group 15 (5A): -3
Redox Reactions
- Redox reactions involve the transfer of electrons between oxidized and reduced species.
- Increased oxidation state indicates oxidation, while a decrease indicates reduction.
- The oxidizing agent is the substance that gains electrons, while the reducing agent loses electrons.
Half-Reactions
- Each reactant's fate can be expressed in half-reactions:
- Oxidation half-reaction: shows loss of electrons.
- Reduction half-reaction: shows gain of electrons.
- Example reactions reflect clear roles of oxidized and reduced species, along with ionic forms as solids.
Mnemonics for Oxidation and Reduction
- "LeO says GeR":
- Loses electrons = Oxidation
- Gains electrons = Reduction
- "Oil Rig":
- Oxidation Is Loss
- Reduction Is Gain
Balancing Half-Reactions in Acidic Solutions
- Balance oxidation and reduction half-reactions by:
- Ensuring equal atoms of interest.
- Adding H₂O to balance oxygen atoms.
- Adding H⁺ ions for hydrogen atoms.
- Adding electrons to balance charge.
Example Half-Reactions
- Iron and copper interaction:
- Oxidation: Fe → Fe²⁺ + 2e⁻
- Reduction: Cu²⁺ + 2e⁻ → Cu
- Sulfur and manganese interaction:
- Oxidation: SO₃²⁻ → SO₄²⁻ + 2H⁺ + 2e⁻
- Reduction: MnO₄⁻ + 8H⁺ + 5e⁻ → MnO₂ + 4H₂O
General Principles of Redox
- Redox reactions can be represented as a process involving clear agents and product formation characterized by their oxidation states.
- Understanding the oxidation state changes is crucial for predicting reaction outcomes and balancing equations effectively.
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