Redox Reactions Quiz

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Questions and Answers

What is the correct definition of oxidation in redox reactions?

  • Gaining electrons by an atom, ion, or molecule
  • Losing protons by an atom, ion, or molecule
  • Gaining neutrons by an atom, ion, or molecule
  • Losing electrons by an atom, ion, or molecule (correct)

In the reaction of sodium and chlorine, which statement correctly describes sodium's role?

  • Sodium is reduced because it gains electrons
  • Sodium acts as an oxidizing agent in the reaction
  • Sodium is oxidized because it loses electrons (correct)
  • Sodium has no role in the redox reaction

What is the substance called that gains electrons during a redox reaction?

  • Oxidizing agent (correct)
  • Reducing agent
  • Catalyst
  • Electrolyte

In the reaction 2H2 + O2 → 2H2O, what happens to the oxidation state of hydrogen?

<p>It increases from 0 to +1 (D)</p> Signup and view all the answers

What does the acronym OIL RIG help to remember in the context of redox reactions?

<p>Oxidation Is Losing, Reduction Is Gaining (B)</p> Signup and view all the answers

In the reaction Zn + CuSO4 → ZnSO4 + Cu, what is the change in oxidation state for zinc?

<p>Increases from 0 to +2 (B)</p> Signup and view all the answers

Why are redox reactions crucial in biological processes?

<p>They produce ATP during cellular respiration (D)</p> Signup and view all the answers

What role does the oxidizing agent play in a redox reaction?

<p>It gains electrons and causes another to be oxidized (B)</p> Signup and view all the answers

What is the oxidation number of sulfur in H₂SO₄?

<p>+6 (B)</p> Signup and view all the answers

What must be true about the sum of oxidation numbers in a polyatomic ion?

<p>It equals the charge of the ion. (C)</p> Signup and view all the answers

What is the oxidation number of manganese in MnO₂?

<p>+4 (A)</p> Signup and view all the answers

Which element is oxidized in the given reaction: MnO₄⁻ + C₂O₄²⁻ → Mn²⁺ + CO₂?

<p>Carbon (C)</p> Signup and view all the answers

How do you determine the oxidation number of an element within a neutral compound?

<p>By ensuring the sum of oxidation numbers is zero. (A)</p> Signup and view all the answers

What is the role of oxidation numbers in redox reactions?

<p>They track the movement of electrons. (A)</p> Signup and view all the answers

What is the oxidation number of chlorine in NaCl?

<p>-1 (C)</p> Signup and view all the answers

Which step is performed first when balancing a redox equation using oxidation numbers?

<p>Assign oxidation numbers to all elements. (B)</p> Signup and view all the answers

In the reaction 2MnO₄⁻ + 16H⁺ + 5C₂O₄²⁻ → 2Mn²⁺ + 8H₂O + 10CO₂, what is the total charge on the reactant side?

<p>+7 (C)</p> Signup and view all the answers

What is the final balanced equation for the reaction involving MnO₄⁻ and C₂O₄²⁻?

<p>2MnO₄⁻ + 16H⁺ + 5C₂O₄²⁻ → 2Mn²⁺ + 8H₂O + 10CO₂ (B)</p> Signup and view all the answers

In which situation is the oxidation number method particularly useful?

<p>When balancing reactions in acidic or basic solutions. (D)</p> Signup and view all the answers

What is the oxidation number of oxygen in most compounds?

<p>-2 (D)</p> Signup and view all the answers

What is the reduction half-reaction for Mn in the reaction with MnO₄⁻?

<p>MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O (C)</p> Signup and view all the answers

What happens to the oxidation number of manganese as it is reduced in MnO₄⁻?

<p>It decreases from +7 to +2. (A)</p> Signup and view all the answers

In the reaction Fe + O$_2$ → Fe$_2$O$_3$, what type of process is occurring?

<p>Oxidation (C)</p> Signup and view all the answers

Which substance acts as the oxidizing agent in the reaction 2H$_2$ + O$_2$ → 2H$_2$O?

<p>Oxygen (B)</p> Signup and view all the answers

What is the oxidation half-reaction for zinc in the reaction Zn + CuSO$_4$ → ZnSO$_4$ + Cu?

<p>Zn(s) → Zn$^{2+}$ + 2e$^-$ (A)</p> Signup and view all the answers

Which of the following correctly describes a reducing agent?

<p>Loses electrons and is oxidized (A)</p> Signup and view all the answers

How is an oxidation number defined?

<p>The hypothetical charge an atom would have if electrons were completely transferred (C)</p> Signup and view all the answers

In which scenario does oxygen have an oxidation number of -1?

<p>In hydrogen peroxide (H$_2$O$_2$) (B)</p> Signup and view all the answers

What does a reduction half-reaction illustrate?

<p>The substance gaining electrons with electrons on the reactant side (B)</p> Signup and view all the answers

What happens to the oxidation state of hydrogen in H$_2$ when it reacts with metals in hydrides?

<p>It becomes -1 (B)</p> Signup and view all the answers

Which is true regarding the overall redox reaction Zn + Cu$^{2+}$ → Zn$^{2+}$ + Cu?

<p>Copper is reduced while zinc is oxidized (B)</p> Signup and view all the answers

What is the rule for the oxidation number of elements in their pure form?

<p>It is always 0 (C)</p> Signup and view all the answers

What is expected of the sum of oxidation numbers in a neutral compound?

<p>It must equal zero (A)</p> Signup and view all the answers

Which of the following elements always has an oxidation number of -1?

<p>Fluorine (B)</p> Signup and view all the answers

Flashcards

Redox Reaction

A chemical reaction where atoms change their oxidation states. It involves loss and gain of electrons.

Oxidation

The process where an atom, ion, or molecule loses electrons. Its oxidation state increases.

Reduction

The process where an atom, ion, or molecule gains electrons. Its oxidation state decreases.

Oxidizing Agent

The substance that gains electrons and causes the oxidation of another substance.

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Reducing Agent

The substance that loses electrons and causes the reduction of another substance.

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Half-Reaction

Breaking down a redox reaction into separate oxidation and reduction half-reactions.

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Oxidation States

A way to identify redox reactions by tracking changes in the oxidation states of elements.

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Redox Reactions and Energy

Redox reactions are essential for energy production in biological processes like cellular respiration and combustion.

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Writing half-reactions

The process of splitting a redox reaction into two separate equations, one representing oxidation and the other representing reduction.

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Oxidation number

The charge an atom would have if the compound was made of ions, assuming complete electron transfer in bonds.

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Oxidation number rule 1

The oxidation number of an element in its pure elemental form is zero.

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Oxidation number rule 2

The oxidation number of a monoatomic ion is equal to its charge.

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Oxidation number rule 3

Oxygen generally has an oxidation number of -2, except in peroxides or when bonded to fluorine.

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Oxidation number rule 4

Hydrogen generally has an oxidation number of +1, except when combined with metals in hydrides.

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Oxidation number rule 5

Fluorine always has an oxidation number of -1, as it is the most electronegative element.

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Oxidation number rule 6

The sum of the oxidation numbers of all atoms in a neutral compound must equal zero.

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Oxidation numbers in chemistry

A way to track the movement and distribution of electrons in molecules and compounds.

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Polyatomic Ion Rule

The sum of the oxidation numbers of all atoms in a polyatomic ion must equal the overall charge of the ion.

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Neutral Molecule Rule

In a neutral molecule, the sum of the oxidation numbers of all atoms is zero. This principle helps determine the oxidation number of an element in a molecule.

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Assigning Oxidation Numbers

The process of assigning oxidation numbers to elements in a compound or ion, based on a set of rules.

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Half-Reaction Diagram

A way to visually represent the half-reactions of a redox reaction, showing the electron transfer.

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Balancing Redox Reactions

Balancing redox reactions in acidic or basic solutions by using the oxidation number method, ensuring conservation of mass and charge.

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Redox Reaction Analysis

Identifying elements that are oxidized and reduced in a redox reaction by examining changes in oxidation numbers.

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Elemental Oxidation Number

The oxidation number of an element in its pure elemental form is always zero.

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Oxidation Number Range

An oxidation number can be positive, negative, or even zero, depending on the element's role in a compound or ion.

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Oxidation Number Importance

Oxidation numbers are a powerful tool used to track electron transfer in redox reactions and understand the changes in chemical species.

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Neutral Compound Rule

The sum of the oxidation numbers in a neutral compound is always zero.

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Study Notes

Redox Reactions

  • Redox reactions, or reduction-oxidation reactions, involve changes in oxidation states of elements
  • Oxidation: Loss of electrons by an atom, ion, or molecule; an increase in oxidation state
  • Reduction: Gain of electrons by an atom, ion, or molecule; a decrease in oxidation state
  • OIL RIG: Oxidation Is Losing; Reduction Is Gaining
  • Redox reactions occur simultaneously: one substance is oxidized (loses electrons), and another is reduced (gains electrons)

Oxidizing and Reducing Agents

  • Oxidizing agent: Gains electrons, causes another substance to lose electrons (oxidize); gets reduced (acquires electrons)
  • Reducing agent: Loses electrons, causes another substance to gain electrons (reduce); gets oxidized (loses electrons)
  • Example: hydrogen-oxygen reaction: oxygen is the oxidizing agent; hydrogen is the reducing agent

How to Identify Redox Reactions:

  • Write half-reactions
  • Determine electron transfer
  • Recognize changes in oxidation states

Oxidation States:

  • Oxidation state: hypothetical charge an atom would have if all bonds were ionic
  • Rules for assigning oxidation states:
    • Pure elements have an oxidation state of zero
    • Monoatomic ion's oxidation state equals its charge
    • Oxygen usually has an oxidation state of -2 (except in peroxides, where it's -1, or bonded to fluorine)
    • Hydrogen usually has an oxidation state of +1 (except in hydrides, where it's -1)
    • Fluorine always has an oxidation state of -1
    • The sum of oxidation states in a neutral compound is zero; in a polyatomic ion, it equals the ion's charge

Half-Reactions

  • Half-reaction: an equation representing either oxidation or reduction in a redox reaction.
  • Oxidation half-reaction: Shows the loss of electrons (substance gets oxidized)
  • Reduction half-reaction: Shows the gain of electrons (substance gets reduced)
  • Example: Zinc-Copper Sulfate reaction:
    • Oxidation half-reaction: Zn(s) → Zn²⁺(aq) + 2e⁻
    • Reduction half-reaction: Cu²⁺(aq) + 2e⁻ → Cu(s)

Balancing Redox Reactions (Oxidation Number Method)

  • Steps:
    • Write the unbalanced reaction
    • Assign oxidation states to all atoms
    • Identify oxidation and reduction half-reactions
    • Write the half-reactions, ensuring they are balanced for mass and charge
    • Multiply half-reactions to have equal numbers of electrons gained/lost
    • Combine the half-reactions to obtain the balanced equation
  • Example: MnO₄⁻ + C₂O₄²⁻ → Mn²⁺+ CO₂ (balanced equation shown earlier)

Importance of Redox Reactions:

  • Energy production (e.g., cellular respiration)
  • Corrosion (e.g., rusting of iron)
  • Batteries (e.g., electrochemical reactions in batteries)

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