Ionic Equilibrium JEE Study Notes

1. Arrhenius Theory of Electrolytic Dissociation

• Ions are formed when ionic compounds dissolve in water or other polar solvents.
• Strong electrolytes dissociate completely, while weak electrolytes dissociate partially.
• The degree of dissociation is determined by the strength of the acid or base.
• [Reference: NCERT Class 11 Chemistry, Chapter 12: States of Matter]

2. Ionic Product of Water (Kw)

• The ionic product of water (Kw) represents the equilibrium between water molecules and hydrogen and hydroxide ions.
• At 25°C, Kw = [H+][OH-] = 1 x 10^-14
• Kw increases with temperature.
• [Reference: NCERT Class 11 Chemistry, Chapter 12: States of Matter]

3. pH and pOH

• pH is the negative logarithm of the hydrogen ion concentration [H+].
• pOH is the negative logarithm of the hydroxide ion concentration [OH-].
• pH + pOH = 14 at 25°C.
• A solution is acidic if pH < 7, basic if pH > 7, and neutral if pH = 7.
• [Reference: NCERT Class 11 Chemistry, Chapter 12: States of Matter]

4. Common Ion Effect

• The common ion effect is the phenomenon in which the presence of a common ion in a solution suppresses the dissociation of a weak electrolyte.
• This effect shifts the equilibrium towards the undissociated form, reducing the concentration of ions in solution.
• [Reference: NCERT Class 11 Chemistry, Chapter 13: Equilibrium]

5. Hydrolysis of Salts

• Hydrolysis is the chemical reaction between a salt and water, resulting in the formation of an acidic, basic, or neutral solution.
• The extent of hydrolysis depends on the strength of the conjugate acid and base of the salt.
• Salts of strong acids and weak bases undergo hydrolysis to produce acidic solutions.
• Salts of weak acids and strong bases undergo hydrolysis to produce basic solutions.
• Salts of weak acids and weak bases undergo hydrolysis to produce neutral solutions.
• [Reference: NCERT Class 11 Chemistry, Chapter 13: Equilibrium]

6. Buffer Solutions

• A buffer solution is a solution that resists changes in pH upon addition of small amounts of acids or bases.
• Buffer solutions consist of a weak acid or base along with its conjugate base or acid.
• The pH of a buffer solution is determined by the Henderson-Hasselbalch equation:

pH = pKa + log ([A-]/[HA])

• where pKa is the dissociation constant of the weak acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.
• [Reference: NCERT Class 11 Chemistry, Chapter 13: Equilibrium]

7. Solubility Product (Ksp)

• The solubility product (Ksp) is the equilibrium constant for the dissolution of a sparingly soluble salt.
• It represents the maximum concentration of ions that can exist in a solution before precipitation occurs.
• The Ksp of a salt is determined by the temperature and solvent.
• [Reference: NCERT Class 12 Chemistry, Chapter 4: Chemical Kinetics]

8. Acid-Base Equilibria in Salt Solutions

• When a salt of a weak acid or base is dissolved in water, it undergoes hydrolysis.
• The resulting solution may be acidic, basic, or neutral, depending on the strength of the conjugate acid and base.
• The equilibrium constant for the hydrolysis reaction is called the hydrolysis constant (Kh).
• The pH of the solution can be calculated using the Henderson-Hasselbalch equation.
• [Reference: NCERT Class 12 Chemistry, Chapter 5: Surface Chemistry]