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Questions and Answers
What is the oxidation number of elements in their elemental form?
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Define oxidation and reduction in terms of electron transfer.
Oxidation is the loss of electrons, while reduction is the gain of electrons.
In the reaction 2Mg + O2 → 2MgO, which reactant is oxidized and which is reduced?
Mg is oxidized, and O2 is reduced.
What is the oxidation number of oxygen in peroxides?
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Identify the oxidizing agent in the reaction MnO4– + H2C2O4 → Mn2+ + CO2.
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What must be done to balance oxygen atoms in half-reactions?
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How should you adjust half-reactions to have the same number of electrons for summation?
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What is the oxidation number of hydrogen when bonded to metals?
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In a redox reaction, what is the primary role of the reducing agent?
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What is the systematic rule for determining oxidation numbers in Group II elements?
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What are the products formed when zinc reacts with nitrate ions in basic solution?
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After adding OH– ions to both sides of a half-reaction, what should be done with H+ ions?
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In the overall balanced equation 2MnO4– + 6H+ + 5H2C2O4 → 2Mn2+ + 10CO2 + 8H2O, what is the main charge balance required?
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Which element in the activity series can reduce Cu2+ ions?
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What should be done if H2O is present on both sides of a half-reaction during redox balancing?
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In the equation 4Zn + 7OH– + NO3– + 6H2O → 4Zn(OH)42– + NH3, how is oxygen balanced?
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Describe the significance of combining half-reactions in the balancing process.
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What is the role of KMnO4 in redox reactions under acidic conditions?
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What happens to the manganese ion during the reaction of 2MnO4– in acidic solution?
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In the reaction Br– → BrO3–, what type of reaction is occurring?
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Study Notes
Oxidation Numbers
- The oxidation number of an atom is its effective charge.
- An elemental substance has an oxidation number of zero.
- The oxidation number of a monoatomic ion equals its charge.
- The sum of oxidation numbers of all atoms in a species equals its total charge.
- Group 1 elements have an oxidation number of +1.
- Group 2 elements have an oxidation number of +2.
- Group 3 elements (except boron) have an oxidation number of +3 for M³⁺ and +1 for M⁺.
- Group 4 elements (except carbon and silicon) have an oxidation number of +4 for M⁴⁺ and +2 for M²⁺.
- Hydrogen has an oxidation number of +1 when combined with non-metals, and -1 when combined with metals.
- Fluorine always has an oxidation number of -1 in its compounds.
- Oxygen has an oxidation number of -2 unless combined with fluorine, in peroxides (O₂²⁻) it's -1, in superoxides (O₂⁻) it's -½, and in ozonides (O₃⁻) it's -⅓.
Redox Reactions
- Oxidation refers to electron loss.
- Reduction refers to electron gain.
- A redox reaction is a reaction where both oxidation and reduction occur.
- An oxidizing agent removes electrons and is reduced in a reaction. The element in the oxidizing agent undergoes a decrease in oxidation number.
- A reducing agent supplies electrons and is oxidized in a reaction. The element in the reducing agent undergoes an increase in oxidation number.
Redox Reactions in Acidic Solution
- This section outlines steps to balance redox reactions in acidic solutions using the example of potassium permanganate (KMnO₄) and oxalic acid (H₂C₂O₄) reacting to form Mn²⁺ and CO₂.
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Steps:
- Identify the oxidized and reduced species by looking at the changes in oxidation numbers.
- Write two skeletal equations for the half-reactions.
- Balance all elements (except O, H, and charge) by inspection.
- Balance oxygen atoms by adding H₂O to each half-reaction.
- Balance hydrogen atoms by adding H⁺ to each half-reaction.
- Balance the electric charges in each half-reaction by adding electrons.
- Multiply each half-reaction by a factor to equalize the number of electrons.
- Combine the two balanced half-reactions by adding them together to form a single balanced equation.
- Check the balanced equation by verifying the number of atoms and the net charge on each side.
Redox Reactions in Basic Solution
- Balancing redox reactions in basic solution is similar to acidic solution, with additional steps:
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Steps:
- Follow steps 1 to 5 from acidic solution balancing.
- Add the same number of OH⁻ ions to both sides of the equation as there are H⁺ ions in each half-reaction.
- Combine H⁺ and OH⁻ on each side of the equation to form H₂O.
- Move H₂O molecules to one side of the equation if present on both sides.
- Continue with Step 6 from acidic solution balancing.
Element Activity Series
- This is a list of elements ordered by their reactivity.
- A metal can reduce the cations formed by any metal below it in the list.
- For example, Zinc (Zn) can reduce Cu²⁺, but copper (Cu) cannot reduce Zn²⁺.
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Description
Test your knowledge on oxidation numbers and redox reactions. This quiz covers essential concepts, including the effective charge of atoms and the rules governing oxidation states. Perfect for students studying general chemistry.
