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 provides a molecular look at acids and bases through the lens of both Brønsted–Lowry and Lewis theories. It emphasizes proton donor–acceptor interactions, introduces conjugate acid–base pairs and amphoteric substances, and explains how equilibrium positions and periodic trends dictate acid and base strengths. A practical application is highlighted in the production of advanced ceramics via sol–gel synthesis, demonstrating the real-world importance of these chemical principles.

Learning Objectives

1

Describe the Brønsted–Lowry and Lewis definitions of acids and bases and their molecular interactions.

2

Explain the concept of conjugate acid–base pairs and recognize amphoteric substances.

3

Analyze acid and base strengths through equilibrium positions and periodic trends in binary acids and oxoacids.

4

Interpret the role of acid–base reactions in practical applications, such as advanced ceramics via sol–gel synthesis.

5

Develop problem-solving strategies for acid–base chemistry using provided tools and review questions.

Key Concepts

CONCEPT

DEFINITION

Brønsted–Lowry Acid

A substance that donates a proton (H⁺) to another substance during a chemical reaction.

Brønsted–Lowry Base

A substance that accepts a proton (H⁺) during a chemical reaction.

Conjugate Acid–Base Pair

Two species that transform into each other by the gain or loss of a proton.

Amphoteric/Amphiprotic Substance

A compound that can act as either an acid or a base depending on the reaction conditions.

Lewis Acid

An electron pair acceptor that participates in chemical reactions by accepting an electron pair.

Lewis Base

An electron pair donor that forms a chemical bond by donating an electron pair.

Periodic Trends in Acidity

Trends that explain variations in acid strength across different elements, including binary acids and oxoacids, based on their position in the periodic table.

Sol–Gel Synthesis

A method for producing advanced ceramics and other materials involving the transition of a system from a liquid 'sol' into a solid 'gel'.

Example Problems

Example 1

How is a Brønsted-Lowry acid defined? How is a BrønstedLowry base defined? How do these definitions differ from the Arrhenius definition of acids and bases?

Example 2

How are the formulas of the members of a conjugate acid-base pair related to each other? Within the pair, how can you tell which is the acid?

Example 3

Is $\mathrm{H}_{2} \mathrm{SO}_{4}$ the conjugate acid of $\mathrm{SO}_{4}^{2-}$ ? Explain your answer.

Example 4

What is meant by the term amphoteric? Give two chemical equations that illustrate the amphoteric nature of water.

Example 5

Define the term amphiprotic.
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Step-by-Step Explanations

QUESTION

Given the reaction: HA + B → A⁻ + HB⁺, identify the conjugate base.

STEP-BY-STEP ANSWER:

Step 1: Recognize that HA is the acid because it donates a proton.
Step 2: When HA loses a proton (H⁺), it becomes A⁝.
Step 3: Identify A⁝ as the conjugate base of the acid HA.
Final Answer: A⁝ is the conjugate base.

Determining the Conjugate Base in a Brønsted–Lowry Reaction

QUESTION

How does the position of the equilibrium indicate the strength of an acid in its dissociation reaction?

STEP-BY-STEP ANSWER:

Step 1: Write the general dissociation reaction: HA ⇌ H⁺ + A⁻.
Step 2: Understand that a strong acid dissociates almost completely, shifting the equilibrium to the right.
Step 3: Recognize that if the equilibrium lies far to the right, the acid is strong; if it lies to the left, the acid is weak.
Final Answer: The further the equilibrium shifts to the right, the stronger the acid.

Evaluating Acid Strength Using Equilibrium Concepts

QUESTION

Explain how a Lewis acid–base interaction differs from a Brønsted–Lowry reaction.

STEP-BY-STEP ANSWER:

Step 1: Identify that the Brønsted–Lowry model focuses on proton transfer between species.
Step 2: The Lewis model instead involves the transfer of an electron pair.
Step 3: In a Lewis acid–base reaction, the Lewis acid accepts an electron pair, while the Lewis base donates it.
Final Answer: Unlike the proton transfer in Brønsted–Lowry reactions, Lewis acid–base reactions center around electron pair transfers.

Applying Lewis Acid–Base Theory

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Common Mistakes

  • Confusing acid–base reactions with redox reactions, leading to misidentification of the active species.
  • Assuming that all acid–base reactions strictly follow the Brønsted–Lowry model without considering Lewis acid–base interactions.
  • Overlooking the role of conjugate pairs, which can lead to misunderstanding reaction equilibria and acid strength.
  • Neglecting periodic trends that affect the strength of acids, especially in the case of binary acids versus oxoacids.