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Questions and Answers
What is the oxidation number of an atom in its elemental form?
What is the oxidation number of an atom in its elemental form?
What is the oxidation number of oxygen in a peroxide?
What is the oxidation number of oxygen in a peroxide?
What is the sum of the oxidation numbers of all atoms in a neutral compound?
What is the sum of the oxidation numbers of all atoms in a neutral compound?
What occurs at an electrode during a half-cell reaction?
What occurs at an electrode during a half-cell reaction?
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What is the direction of electron flow in an oxidation half-cell?
What is the direction of electron flow in an oxidation half-cell?
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What is the notation format for half-cell reactions?
What is the notation format for half-cell reactions?
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What is the oxidation number of fluorine in a compound?
What is the oxidation number of fluorine in a compound?
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What type of reaction occurs at a cathode?
What type of reaction occurs at a cathode?
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What is the sum of the oxidation numbers of all atoms in a polyatomic ion?
What is the sum of the oxidation numbers of all atoms in a polyatomic ion?
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What type of reaction is Zn → Zn²⁺ + 2e⁻?
What type of reaction is Zn → Zn²⁺ + 2e⁻?
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Study Notes
Oxidation Numbers
- Definition: Oxidation numbers (also known as oxidation states) are a way to keep track of electrons during a redox reaction.
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Rules for Assigning Oxidation Numbers:
- The oxidation number of an atom in its elemental form is zero.
- The oxidation number of a monatomic ion is equal to its charge.
- In compounds, the oxidation number of oxygen is typically -2, except in peroxides (H2O2) where it is -1.
- The oxidation number of hydrogen is typically +1, except in hydrides (NaH) where it is -1.
- The oxidation number of fluorine is always -1.
- The sum of the oxidation numbers of all atoms in a neutral compound is zero.
- The sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion.
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Examples:
- NaCl: Na (+1), Cl (-1)
- H2O: H (+1), O (-2)
- CaO: Ca (+2), O (-2)
Half-cell Reactions
- Definition: A half-cell reaction is a reduction or oxidation reaction that occurs at an electrode during a redox reaction.
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Characteristics:
- Half-cell reactions involve the transfer of electrons.
- They can be either oxidation (loss of electrons) or reduction (gain of electrons) reactions.
- They occur at an electrode, which can be an anode (oxidation) or a cathode (reduction).
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Notation:
- Half-cell reactions are often written in the format:
oxidized species → reduced species - The reaction is often divided into two parts: the oxidation half-cell and the reduction half-cell.
- Half-cell reactions are often written in the format:
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Examples:
- Oxidation half-cell:
Zn → Zn²⁺ + 2e⁻ - Reduction half-cell:
Cu²⁺ + 2e⁻ → Cu - Overall reaction:
Zn + Cu²⁺ → Zn²⁺ + Cu
- Oxidation half-cell:
Oxidation Numbers
- Oxidation numbers track electrons during redox reactions.
Rules for Assigning Oxidation Numbers
- Atoms in elemental form have an oxidation number of zero.
- Monatomic ions have an oxidation number equal to their charge.
- Oxygen has an oxidation number of -2 in compounds, except -1 in peroxides.
- Hydrogen has an oxidation number of +1 in compounds, except -1 in hydrides.
- Fluorine always has an oxidation number of -1.
- In neutral compounds, the sum of oxidation numbers is zero.
- In polyatomic ions, the sum of oxidation numbers equals the ion's charge.
Oxidation Number Examples
- NaCl: Na is +1, Cl is -1.
- H2O: H is +1, O is -2.
- CaO: Ca is +2, O is -2.
Half-cell Reactions
- Half-cell reactions are reduction or oxidation reactions at an electrode during redox reactions.
Characteristics of Half-cell Reactions
- They involve electron transfer.
- They can be oxidation (electron loss) or reduction (electron gain) reactions.
- They occur at an electrode: anode (oxidation) or cathode (reduction).
Notation for Half-cell Reactions
- Format:
oxidized species → reduced species. - Divided into oxidation and reduction half-cells.
Half-cell Reaction Examples
- Oxidation half-cell:
Zn → Zn²⁺ + 2e⁻. - Reduction half-cell:
Cu²⁺ + 2e⁻ → Cu. - Overall reaction:
Zn + Cu²⁺ → Zn²⁺ + Cu.
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Description
Learn about oxidation numbers, also known as oxidation states, and how to assign them according to specific rules in chemistry. Understand the importance of tracking electrons during redox reactions.
