Book cover for Chemistry: The Molecular Nature of Matter

Chemistry: The Molecular Nature of Matter

Neil D. Jespersen, James E. Brady, Alison Hyslop

ISBN #9781118413920

7th Edition

3,064 Questions

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53,557 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter on Oxidation–Reduction Reactions introduces the core principles of electron transfer between reactants, defines fundamental terms such as oxidation, reduction, and oxidation numbers, and presents the ion–electron method for balancing redox equations in various media. It also discusses the activity series of metals for predicting displacement reactions and explores practical applications like redox titrations and combustion phenomena, providing a comprehensive toolbox for solving redox problems and understanding their real-world relevance.

Learning Objectives

1

Explain the fundamental principles of oxidation–reduction reactions and electron transfer between reactants.

2

Define key terms such as oxidation, reduction, and oxidation numbers.

3

Apply the ion–electron method to balance redox equations in both acidic and basic media.

4

Utilize the activity series of metals to predict displacement reactions.

5

Analyze practical applications of redox reactions including redox titrations and combustion phenomena.

Key Concepts

CONCEPT

DEFINITION

Oxidation–Reduction (Redox) Reactions

Chemical reactions involving the transfer of electrons from one reactant to another.

Oxidation

The process in which a substance loses electrons.

Reduction

The process in which a substance gains electrons.

Oxidation Number

A value assigned to an element in a compound that represents its degree of oxidation or reduction.

Ion–Electron Method

A systematic approach used to balance redox equations by separately balancing the oxidation and reduction half-reactions.

Activity Series of Metals

A ranking of metals based on their ability to displace other metals in a chemical reaction.

Redox Titration

A titration method that involves a redox reaction between the titrant and the analyte to determine concentration.

Combustion Phenomena

Chemical reactions typically involving oxygen in which a substance reacts rapidly and releases energy in the form of heat and light.

Example Problems

Example 1

Define oxidation and reduction in terms of (a) electron transfer and (b) oxidation numbers.

Example 2

Why must both oxidation and reduction occur simultaneously during a redox reaction? What is an oxidizing agent and what happens to it in a redox reaction? What is a reducing agent and what happens to it in a redox reaction?

Example 3

In the compound $\mathrm{As}_{4} \mathrm{O}_{6}$, arsenic has an oxidation $\mathrm{num}$ ber of +3 . What is the oxidation state of arsenic in this compound?

Example 4

Are the following redox reactions? Explain. $$ \begin{aligned} 2 \mathrm{NO}_{2} & \longrightarrow \mathrm{N}_{2} \mathrm{O}_{4} \\ 2 \mathrm{CrO}_{4}^{2-}+2 \mathrm{H}^{+} & \longrightarrow 2 \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+\mathrm{H}_{2} \mathrm{O} \end{aligned} $$

Example 5

If the oxidation number of nitrogen in a certain molecule changes from +3 to -2 during a reaction, is the nitrogen oxidized or reduced? How many electrons are gained or lost by the nitrogen atom?
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Step-by-Step Explanations

QUESTION

How do you balance a redox equation using the ion–electron method in an acidic medium?

STEP-BY-STEP ANSWER:

Step 1: Separate the overall reaction into oxidation and reduction half-reactions.
Step 2: Balance all atoms in each half-reaction except oxygen and hydrogen.
Step 3: Balance oxygen atoms by adding water (H₂O) molecules.
Step 4: Balance hydrogen atoms by adding hydrogen ions (Hâș).
Step 5: Balance the electrical charge by adding electrons (e⁻) to the more positive side.
Step 6: Multiply each half-reaction by appropriate factors so that the number of electrons gained equals the number lost.
Step 7: Add the half-reactions together and simplify to obtain the balanced redox equation.
Final Answer: A correctly balanced equation in acidic medium that conserves both mass and charge.

Ion–Electron Method

QUESTION

How can the activity series be used to predict whether a metal will displace another in a redox reaction?

STEP-BY-STEP ANSWER:

Step 1: Identify the two metals involved in the reaction.
Step 2: Consult the activity series to determine the relative reactivity of the metals.
Step 3: The metal higher in the activity series is more reactive and can displace the metal lower in the series from its compound.
Step 4: Write the corresponding half-reactions to represent the oxidation of the more reactive metal and the reduction of the less reactive metal.
Step 5: Combine the reactions to predict the overall reaction.
Final Answer: The metal higher in the activity series will displace the lower one, leading to a spontaneous redox reaction.

Using the Activity Series

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Common Mistakes

  • Failing to identify and separate the oxidation and reduction half-reactions before balancing.
  • Incorrectly balancing the number of electrons exchanged between half-reactions.
  • Confusing oxidation with reduction or mixing up the assigned oxidation numbers.
  • Neglecting to adjust for the medium (acidic or basic) when adding water, H?, or OH?.
  • Overlooking the proper use of the activity series, leading to incorrect predictions of metal displacement reactions.