Equilibrium II (Ionic Equilibrium) – NEET Chemistry Class 11

Ionic equilibrium deals with the behavior of ions in aqueous solutions, including acids, bases, salts, and their reactions. This chapter introduces key concepts such as pH, hydrolysis, buffer solutions, and the common ion effect, which are crucial for understanding chemical equilibria in ionic systems and for NEET exam preparation.

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Introduction to Ionic Equilibrium

In aqueous solutions, many salts, acids, and bases dissociate into ions. The equilibrium between the dissociated ions and undissociated species is known as ionic equilibrium. This equilibrium governs properties like pH, buffer action, and the solubility of salts.

Acid-Base Equilibrium

Acid-base reactions involve proton transfer. Key concepts include:

• Arrhenius, Brønsted-Lowry, and Lewis definitions of acids and bases.

• Ionization constant of water (Kw): At 25°C, Kw = 1 × 10⁻¹⁴.

• pH and pOH: pH = -log[H⁺], pOH = -log[OH⁻], and pH + pOH = 14.

Acid-base equilibrium is fundamental for understanding reaction strengths and the effect of dilution.

Salt Hydrolysis

Salt hydrolysis occurs when salts react with water to produce acidic or basic solutions. Types of salts include:

1. Acidic Salts – Derived from strong acids and weak bases.

2. Basic Salts – Derived from weak acids and strong bases.

3. Neutral Salts – Derived from strong acids and strong bases.

The extent of hydrolysis depends on the strength of the parent acid or base.

Buffer Solutions

A buffer solution resists changes in pH upon the addition of small amounts of acid or base. Types of buffers include:

1. Acidic Buffers – Mixture of weak acid and its salt. Example: CH₃COOH + CH₃COONa.

2. Basic Buffers – Mixture of weak base and its salt. Example: NH₄OH + NH₄Cl.

Buffer solutions are essential in biological systems and chemical experiments.

Common Ion Effect

The common ion effect occurs when a solution already contains an ion present in a weak electrolyte, suppressing its ionization. It is important in:

• Reducing the solubility of salts.

• Maintaining buffer pH stability.

Solubility Product (Ksp)

The solubility product is the product of ion concentrations at saturation for a sparingly soluble salt. It helps predict:

• Whether precipitation will occur.

• Effects of ionic strength and common ions on solubility.

Example: For AgCl, Ksp = [Ag⁺][Cl⁻] at equilibrium.

Importance for NEET Preparation

Ionic equilibrium is highly significant for NEET because:

• Questions test conceptual understanding of acids, bases, and salts.

• Numerical problems on pH, hydrolysis, and solubility are frequently asked.

• Buffer solutions and common ion effect are repeated topics in previous year papers.

Previous Year NEET Questions – Insights

Typical questions include:

• Calculating pH and pOH of acidic, basic, and neutral solutions.

• Predicting the outcome of salt hydrolysis.

• Understanding and applying buffer action.

• Solving problems involving common ion effect and Ksp.

Study Tips for Students

1. Focus on Key Formulas – pH, pOH, Kw, Ksp, and hydrolysis constant.

2. Practice Numerical Problems – Especially on buffer solutions and solubility equilibria.

3. Understand Concepts – Acid/base strength, salt hydrolysis, and buffer action.

4. Visualize Buffers and Common Ion Effects – Diagrams help retain understanding.

5. Refer to NCERT – Most NEET questions are NCERT-based.

Conclusion

Mastering Ionic Equilibrium is critical for NEET success. It enables students to calculate pH, understand buffer solutions, predict solubility, and solve both conceptual and numerical questions with confidence. This chapter forms the basis for further studies in chemical kinetics, thermodynamics, and analytical chemistry.