Redox Reactions Overview

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Questions and Answers

What is the definition of oxidation?

The addition of oxygen/electronegative element to a substance or the removal of hydrogen/electropositive element from a substance.

What does "redox" stand for?

Reduction-oxidation

What is an oxidizing agent?

A reagent that increases the oxidation number of an element in a given substance.

What is a reducing agent?

<p>A reagent that lowers the oxidation number of an element in a given substance.</p> Signup and view all the answers

What does oxidation number denote?

<p>The oxidation state of an element in a compound.</p> Signup and view all the answers

What is the oxidation number in the elemental state?

<p>Zero</p> Signup and view all the answers

What is the oxidation number of oxygen in most compounds?

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

What is the oxidation number of a monatomic ion?

<p>Equal to its charge.</p> Signup and view all the answers

Where does the oxidation number of hydrogen deviate from +1?

<p>When it is bonded to metals in binary compounds.</p> Signup and view all the answers

What is the oxidation number of fluorine in all its compounds?

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

What is the algebraic sum of oxidation numbers of all atoms in a compound?

<p>Zero</p> Signup and view all the answers

All decomposition reactions are redox reactions.

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

The reaction between zinc and copper nitrate is a displacement reaction.

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

What type of reaction is the combination of carbon with oxygen to form carbon dioxide?

<p>Combination reaction</p> Signup and view all the answers

What type of reaction is the breakdown of hydrogen peroxide into water and oxygen?

<p>Decomposition reaction</p> Signup and view all the answers

What type of reaction is the displacement of hydrogen from hydrochloric acid by zinc?

<p>Displacement reaction</p> Signup and view all the answers

What type of reaction is the simultaneous reduction and oxidation of the same element?

<p>Disproportionation reaction</p> Signup and view all the answers

The reaction of potassium dichromate with sodium sulphite in an acid solution is an example of a redox reaction?

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

Which of the following statements is NOT true about redox reactions?

<p>All chemical reactions are redox reactions. (D)</p> Signup and view all the answers

Which of the following is NOT an example of a redox reaction?

<p>CaCO3(s) → CaO(s) + CO2(g) (D)</p> Signup and view all the answers

Which of the following statements is true about the concept of oxidation number?

<p>The oxidation number method was developed to keep track of electron shifts in chemical reactions. (C)</p> Signup and view all the answers

Which of the following metals is the most active reducing agent?

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

Which of the following halogens is the strongest oxidizing agent?

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

Which of the following reactions is NOT a disproportionation reaction?

<p>2H2O2(aq) → 2H2O(l) + O2(g) (C)</p> Signup and view all the answers

Which of the following is true about the use of indicators in redox titrations?

<p>Redox indicators are substances that are oxidised or reduced by the analyte, resulting in a colour change (B)</p> Signup and view all the answers

Which of the following statements is NOT true about the standard electrode potential (E) of an electrode?

<p>A positive E value indicates that the redox couple is a stronger reducing agent than the H/H2 couple. (C)</p> Signup and view all the answers

Which of the following is a correct statement about the use of the half-reaction method to balance redox reactions?

<p>The half-reaction method requires balancing the charges and atoms in each half-reaction separately before combining them. (A)</p> Signup and view all the answers

In a galvanic cell, electrons travel from the anode to the cathode through the external circuit.

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

The electrode potential of an electrode is independent of the concentration of the species involved in the electrode reaction.

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

A redox couple consists of an oxidised form and a reduced form of the same species.

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

A salt bridge is used in a galvanic cell to provide a pathway for the flow of electrons between the electrodes.

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

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Flashcards

Redox Reaction

A chemical process involving the transfer of electrons between reactants, resulting in a change in oxidation states.

Reduction

The gain of electrons by a chemical species, resulting in a decrease in its oxidation state.

Oxidation

The loss of electrons by a chemical species, resulting in an increase in its oxidation state.

Oxidizing Agent

A substance that accepts electrons from another substance, causing it to be reduced. The oxidation number of the oxidizing agent decreases during the reaction.

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Reducing Agent

A substance that donates electrons to another substance, causing it to be oxidized. The oxidation number of the reducing agent increases during the reaction.

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Oxidation Number

A number assigned to an atom in a molecule or ion, representing its apparent charge, assuming that electrons are completely transferred.

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Combination Redox Reaction

A chemical reaction where two or more reactants combine to form a single product. At least one of the reactants must be in its elemental form.

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Decomposition Redox Reaction

A chemical reaction where a single reactant breaks down into two or more products. At least one of the products must be in its elemental form.

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Displacement Redox Reaction

A chemical reaction where an atom (or an ion) in a compound is replaced by an atom (or an ion) of another element. It can be categorized into metal displacement and non-metal displacement.

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Disproportionation Redox Reaction

A special type of redox reaction where an element in a particular oxidation state is simultaneously oxidized and reduced. In the reaction, the element is present in at least three oxidation states.

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Acid-Base Reaction

A chemical reaction involving the transfer of protons (H+ ions).

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Acid

A substance that can donate a proton (H+ ion).

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Base

A substance that can accept a proton (H+ ion).

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Redox Reaction

A chemical reaction involving the transfer of electrons between reactants, resulting in a change in oxidation states.

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Reduction

The gain of electrons by a chemical species, resulting in a decrease in its oxidation state.

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Oxidation

The loss of electrons by a chemical species, resulting in an increase in its oxidation state.

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Oxidizing Agent

A substance that accepts electrons from another substance, causing it to be reduced. The oxidation number of the oxidizing agent decreases during the reaction.

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Reducing Agent

A substance that donates electrons to another substance, causing it to be oxidized. The oxidation number of the reducing agent increases during the reaction.

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Oxidation Number

A number assigned to an atom in a molecule or ion, representing its apparent charge, assuming that electrons are completely transferred.

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Combination Redox Reaction

A chemical reaction where two or more reactants combine to form a single product. At least one of the reactants must be in its elemental form.

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Decomposition Redox Reaction

A chemical reaction where a single reactant breaks down into two or more products. At least one of the products must be in its elemental form.

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Displacement Redox Reaction

A chemical reaction where an atom (or an ion) in a compound is replaced by an atom (or an ion) of another element. It can be categorized into metal displacement and non-metal displacement.

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Disproportionation Redox Reaction

A special type of redox reaction where an element in a particular oxidation state is simultaneously oxidized and reduced. In the reaction, the element is present in at least three oxidation states.

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Acid-Base Reaction

A chemical reaction involving the transfer of protons (H+ ions).

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Acid

A substance that can donate a proton (H+ ion).

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Base

A substance that can accept a proton (H+ ion).

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Oxidation Number Method

A method for balancing redox reactions by tracking the changes in oxidation numbers of the reacting species.

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Half Reaction Method

A method for balancing redox reactions by separating the reaction into two half-reactions, one for oxidation and one for reduction, and then combining them.

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Study Notes

Redox Reactions

  • Redox reactions involve simultaneous oxidation and reduction
  • Oxidation is defined as the addition of oxygen or the removal of hydrogen, and gain of electrons
  • Reduction is defined as the removal of oxygen or the addition of hydrogen, and loss of electrons
  • Oxidant (oxidising agent) causes oxidation
  • Reductant (reducing agent) causes reduction

Classical Idea of Redox Reactions

  • Oxidation was originally defined as the addition of oxygen to a substance.
  • Reduction was originally defined as the removal of oxygen to a substance.
  • Oxidation and Reduction are always coupled processes.

Redox Reactions in Terms of Electron Transfer Reactions

  • Oxidation is defined as the loss of electrons, and reduction is defined as the gain of electrons.
  • A redox reaction involves a transfer of electrons.

Competitive Electron Transfer Reactions

  • In a reaction involving zinc and copper nitrate, zinc is oxidised and copper nitrate is reduced.

Oxidation Number

  • Oxidation number is a positive or negative integer assigned to an atom in a compound or ion
  • Rules for assigning oxidation numbers are used to keep track of electrons in redox reactions.

Types of Redox Reactions

  • Combination reactions (e.g., burning of magnesium with oxygen) result in the formation of a new compound.
  • Decomposition reactions (e.g., decomposition of hydrogen peroxide) result in the breakdown of a pre-existing compound.
  • Displacement reactions (e.g., copper nitrate with zinc) involve the replacement of one element by another.
  • Disproportionation reactions (e.g., chlorine reacting with water) an element in an intermediate oxidation state is simultaneously oxidized and reduced

Balancing Redox Reactions

  • Methods for balancing redox reactions, such as the oxidation number method and the half-reaction method, involve balancing atoms and charges.

Redox Reactions as the Basis for Titrations

  • Redox titrations use redox indicators to determine the endpoint of a reaction.

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