Chemistry: Redox Reactions

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Questions and Answers

In the context of chemical reactions, what does the term "redox" refer to?

Redox is a shortened form of "reduction-oxidation", representing chemical reactions where both oxidation and reduction occur simultaneously.

Which of the following is NOT a classical example of an oxidation reaction, based on the original definition?

  • 2 H2S(g) + O2 (g) → 2 S (s) + 2 H2O (l) (correct)
  • CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)
  • 2Mg (s) + O2 (g) → 2MgO (s)
  • S (s) + O2 (g) → SO2 (g)

What is the primary difference between the classical definition of oxidation and the more modern electron-transfer definition?

The classical definition focused on the addition of oxygen or removal of hydrogen. The electron-transfer definition focuses on the loss or gain of electrons during a reaction.

In the reaction represented by the equation: 2Na(s) + Cl2(g) → 2NaCl(s), which species is being oxidized?

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

Which of the following statements accurately describes the electron transfer occurring in a reduction reaction?

<p>Electrons are gained by the species involved in the reaction. (A)</p> Signup and view all the answers

Identify the reducing agent in the following reaction: 2K4Fe(CN)6 + H2O2(aq) → 2K3Fe(CN)6 + 2KOH(aq)

<p>Potassium ferrocyanide (K4[Fe(CN)6]) (B)</p> Signup and view all the answers

The term "oxidation" can ONLY be applied to reactions involving oxygen.

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

In the reaction: Zn(s) + Cu²+(aq) → Zn²+(aq) + Cu(s), which metal is acting as an oxidising agent?

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

What is the purpose of a salt bridge in a Galvanic cell?

<p>The salt bridge allows for the flow of ions between the two half-cells, maintaining electrical neutrality in each half-cell, and completing the circuit for electron flow.</p> Signup and view all the answers

Which of the following correctly describes the concept of oxidation number?

<p>It is a hypothetical charge assigned to an atom in a molecule, assuming all bonds are completely ionic. (B)</p> Signup and view all the answers

The oxidation number of oxygen in peroxides is always -2.

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

What is the significance of the oxidation number in determining whether a reaction is a redox reaction?

<p>A change in the oxidation number of an element during a reaction indicates that it has undergone either oxidation or reduction, thus confirming the reaction is a redox reaction. If there's no change in oxidation number for any element, it is not a redox reaction.</p> Signup and view all the answers

In a combination reaction, which type of species are typically involved?

<p>At least one element in its elemental state (C)</p> Signup and view all the answers

Which of these statements best characterizes a decomposition reaction?

<p>A single substance breaks down into two or more simpler substances. (A)</p> Signup and view all the answers

In a displacement reaction, what is the general outcome?

<p>An element displaces another element from a compound. (A)</p> Signup and view all the answers

All Decomposition reactions are Redox Reactions.

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

What is a disproportionation reaction?

<p>A reaction where a single element in a compound is both oxidized and reduced. (B)</p> Signup and view all the answers

The reaction: 2H2O2(aq) → 2H2O(l) + O2(g) is an example of a disproportionation reaction.

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

Explain the concept of a redox couple.

<p>A redox couple refers to a pair of chemical species that are related by a gain or loss of electrons, one being the oxidized form and the other being the reduced form. These couples are often written as [Oxidized form]/[Reduced form].</p> Signup and view all the answers

What is the significance of the standard electrode potential (E°) value for a redox couple?

<p>The standard electrode potential (E°) value quantifies the tendency of a redox couple to either accept or donate electrons under standard conditions. A more positive E° indicates a stronger oxidizing agent, while a more negative E° indicates a stronger reducing agent.</p> Signup and view all the answers

Which of the following is NOT a key aspect of a redox reaction in the context of electrode processes?

<p>Establishment of an equilibrium between reactants and products. (B)</p> Signup and view all the answers

What is the purpose of using indicators in redox titrations?

<p>Indicators in redox titrations are used to visually signal the endpoint of the reaction. They change color when the titrant has completely reacted with the analyte, indicating that the reaction is complete.</p> Signup and view all the answers

Which of the following is NOT a method used to balance redox reactions?

<p>Law of Mass Action (A)</p> Signup and view all the answers

The oxidation number method for balancing redox reactions primarily considers the change in oxidation numbers and ensures that the total increase in oxidation number equals the total decrease in oxidation number.

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

The half-reaction method for balancing redox reactions involves breaking the reaction into two half-reactions, one representing oxidation and the other representing reduction. It then balances each half-reaction independently before combining them to obtain the balanced overall equation.

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

What is the primary purpose of the ion-electron method for balancing redox reactions?

<p>The ion-electron method focuses on balancing redox reactions in terms of the transfer of electrons and ensuring that the number of electrons lost in oxidation equals the number of electrons gained in reduction.</p> Signup and view all the answers

Explain the concept of "electrolysis" in the context of redox reactions.

<p>Electrolysis is a process where an electric current is used to drive a non-spontaneous chemical reaction. It involves the use of an external power source to force electrons to flow through an electrolytic cell, leading to the oxidation and reduction of species at the electrodes.</p> Signup and view all the answers

Flashcards

Redox reaction

A reaction where oxidation and reduction happen simultaneously.

Oxidation

Loss of electrons or gain of oxygen.

Reduction

Gain of electrons or loss of oxygen.

Oxidant

The substance that gains electrons (or causes oxidation).

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Reductant

The substance that loses electrons (or causes reduction).

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Oxidation number

A number assigned to an element in a compound to keep track of electron transfer.

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Combination reaction (synthesis)

Two or more substances combine to form one new substance.

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Decomposition reaction

A single compound breaks down into two or more simpler substances.

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Displacement reaction

An element replaces another element in a compound.

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Disproportionation reaction

A single substance is both oxidized and reduced at the same time in a reaction.

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Study Notes

Redox Reactions

  • Chemistry is the study of matter and its transformations.
  • Redox reactions are a crucial category of chemical reactions.
  • Redox reactions are involved in many natural and industrial processes.
  • Burning of fuels, metal extraction, and electrochemical processes are examples.
  • Environmental issues like hydrogen economy are also connected to redox.

Classical Idea of Oxidation and Reduction

  • Originally, oxidation was defined as the addition of oxygen to a substance.
  • Reduction was the removal of oxygen from a substance.
  • The scope of these terms broadened to include the addition or removal of hydrogen as well.
  • Reactions with other electronegative elements were also classified as oxidation/reduction.
  • Oxidation and reduction always occur simultaneously.

Redox Reactions in Terms of Electron Transfer

  • In redox reactions, electrons are transferred between species.
  • Oxidation is the loss of electrons.
  • Reduction is the gain of electrons.
  • Oxidising agents (oxidants) accept electrons.
  • Reducing agents (reductants) lose electrons.
  • Redox reactions are crucial in chemical bonding and reactions.

Types of Redox Reactions

  • Combination Reactions: Two or more substances combine to form a new substance.
  • Decomposition Reactions: A compound breaks down into two or more simpler substances.
  • Displacement Reactions: One element in a compound is replaced by another element. It includes metal and non-metal displacement.
  • Disproportionation Reactions: A substance in one oxidation state is simultaneously oxidized and reduced.

Oxidation Numbers

  • Oxidation number represents the hypothetical charge on an atom in a compound.
  • Rules exist for calculating oxidation numbers.
  • The sum of oxidation numbers always adds to the overall charge on the molecule or ion.
  • Oxidation number is also used to denote oxidation states, and is important in redox reactions.

Balancing Redox Equations

  • Oxidation Number Method: A method for balancing redox reactions.
    • Calculate the increase and decrease in oxidation number.
    • Balance the number of atoms/ions.
  • Half-Reaction Method: Another method for balancing redox reactions, which uses half-reactions (oxidation and reduction).
    • Balance each half-reaction separately.
    • Combine to form the balanced redox equation.

Electrode Processes and Galvanic Cells

  • Galvanic cells use redox reactions to generate electrical energy.
    • Oxidation occurs at the anode.
    • Reduction occurs at the cathode.
    • A salt bridge facilitates ion transfer.
  • Standard electrode potential (E°) values help predict feasibility.

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