Book cover for Objective Chemistry for Engineering and Medical Entrance Examinations

Objective Chemistry for Engineering and Medical Entrance Examinations

K Rama Rao

ISBN #9789332541771

1st Edition

2,463 Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter on ionic equilibrium addresses the fundamental principles that govern the behavior of ions in solution, emphasizing the role of solubility, the solubility product constant (Ksp), the common ion effect, and Le Chatelierā€™s Principle. The ability to predict and control the conditions under which ions precipitate or dissolve is crucial for diverse practical applications in various industries, including water treatment, pharmacology, and environmental chemistry.

Learning Objectives

1

Define ionic equilibrium and describe its importance in maintaining a dynamic balance in solutions.

2

Explain the concepts of solubility, Ksp, and the common ion effect in the context of ionic equilibrium.

3

Apply Le Chatelierā€™s Principle to predict how changes in concentration and reaction conditions affect ionic equilibria.

4

Analyze and manipulate ionic equilibria for practical applications in industries such as water treatment, pharmacology, and environmental chemistry.

Key Concepts

CONCEPT

DEFINITION

Ionic Equilibrium

A state in which ionic species in a solution exist in a dynamic balance, with the rate of formation of ions equal to the rate of recombination.

Solubility

The maximum concentration of a solute that can dissolve in a solvent at a given temperature, resulting in a saturated solution.

Ksp (Solubility Product Constant)

A constant that represents the product of the concentrations of the ions in a saturated solution, each raised to the power of their stoichiometric coefficients in the dissolution equation.

Common Ion Effect

The decrease in solubility of an ionic compound when a common ion is added to the solution, shifting the equilibrium according to Le Chatelierā€™s Principle.

Le Chatelierā€™s Principle

A principle stating that if an external change is imposed on a system at equilibrium, the system will adjust in a way that counteracts the change and re-establishes equilibrium.

Example Problems

Example 1

Which of the following statements is false? (l) According to Lewis theory electrophiles are Lewis acids while nucleophiles are Lewis bases. (2) In Friedel-Crafts reaction, the catalysts used are Lewis acids. (3) In complex compounds, metal ions are Lewis bases while ligands are Lewis acids. (4) Electron-deficient molecules are Lewis acids.

Example 2

Which statement is universally correct about an acid and a base? (1) The number of replaceable II-atoms of an acid is called its basicity. (2) \Lambdacids burn skin. (3) $\Lambda$ n acid must contain at least one Il atom. (4) $\Lambda$ n acid turns red litmus to bluc.

Example 3

In water the acids $\mathrm{HClO}_{4}, \mathrm{HCl}, \mathrm{H}_{2} \mathrm{SO}_{4}$ and $\mathrm{HNO}_{3}$ exhibit the same strength as they are completely ionized in water (a base). This is called .......... of the solvent water. (1) Strength (2) Capacity (3) Buffer effect (4) Lcvelling cffect

Example 4

Which is not correct for Lewis acids? (1) They contain at least one vacant orbital. (2) They have a tendency to accept electrons.(3) The smaller ion has greater acidic strength. (4) In case of ions, the strength of acid is inversely proportional to its charge.

Example 5

\Lambdarrange $\mathrm{II}_{2} \mathrm{SO}_{4}(\mathrm{I}), \mathrm{II}_{3} \mathrm{PO}_{4}(\mathrm{II})$ and $\mathrm{IIClO}_{4}$ (III) in decreasing order of acidic naturc. (1) I > III > II (2) $\mathrm{I}>\mathrm{II}>\mathrm{III}$ (3) III $>\mathrm{II}>\mathrm{I}$ (4) $\mathrm{III}>\mathrm{I}>\mathrm{II}$
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Step-by-Step Explanations

QUESTION

How does the introduction of a common ion affect the solubility of an ionic compound?

STEP-BY-STEP ANSWER:

Step 1: Write the dissolution equation for the ionic compound, for example, AB(s) ā‡Œ Aāŗ(aq) + Bā»(aq).
Step 2: Express the Ksp as the product of the ion concentrations, i.e., Ksp = [Aāŗ][Bā»].
Step 3: Recognize that adding a common ion (say Aāŗ) will increase its concentration in the solution.
Step 4: According to Le Chatelierā€™s Principle, the equilibrium shifts to the left to counteract the increase, resulting in decreased dissolution of AB(s).
Step 5: Understand that the solubility of AB decreases due to the shift in equilibrium caused by the added common ion.
Final Answer: The addition of a common ion decreases the solubility of the ionic compound by shifting the dissolution equilibrium towards the undissolved state.

Ksp and the Common Ion Effect

QUESTION

How would a change in concentration of one of the ions in an equilibrium system affect the overall equilibrium?

STEP-BY-STEP ANSWER:

Step 1: Identify the equilibrium reaction and the concentrations of the ions involved.
Step 2: Consider an increase in the concentration of one ion and predict that the system will shift to reduce that ionā€™s concentration.
Step 3: Apply Le Chatelierā€™s Principle by determining which direction (forward or reverse) the equilibrium will shift.
Step 4: Assess the changes in the concentrations of the other ions as the system re-establishes equilibrium.
Final Answer: Increasing the concentration of one ion forces the equilibrium to shift in the direction that decreases that ionā€™s concentration, thereby altering the concentrations of all species in the reaction.

Application of Le Chatelierā€™s Principle

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Common Mistakes

  • Assuming that ionic equilibrium implies a static or unchanging state, rather than a dynamic balance.
  • Confusing the solubility product (Ksp) with the actual solubility of a compound; Ksp is a constant, while solubility can be affected by external conditions.
  • Overlooking the impact of the common ion effect when additional sources of ions are present in the solution.
  • Failing to apply Le Chatelierā€™s Principle correctly, such as not predicting the correct direction of the equilibrium shift after a change in concentration.