Questions and Answers
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 sum of the oxidation numbers of all atoms in a neutral compound?
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?
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What is the notation format for half-cell reactions?
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What is the oxidation number of fluorine in a compound?
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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?
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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.
