Unit-2: Ionic Equilibrium – Core Vocabulary

Vocabulary flashcards summarizing fundamental terms and definitions from Unit-2 Ionic Equilibrium, including electrolytes, ionization, pH, buffers, salt hydrolysis, and solubility product concepts.

Ionic Equilibrium

A dynamic state in which ions produced by the dissociation or ionization of a substance coexist with the undissociated molecules in a polar solvent.

Non-electrolyte

A substance that remains as neutral molecules in solution or molten state and therefore does not conduct electricity (e.g., sugar).

Electrolyte

A substance that dissociates into ions in aqueous or molten state and conducts electricity (e.g., salts, acids, bases).

Strong Electrolyte

An electrolyte that ionizes or dissociates completely in aqueous solution (α ≈ 1).

Weak Electrolyte

An electrolyte that ionizes only partially in aqueous solution, establishing a reversible ionic equilibrium (α ≪ 1).

Degree of Ionization (α)

The fraction of the total number of molecules of an electrolyte that dissociate into ions.

Dielectric Constant

A measure of a solvent’s ability to reduce electrostatic attraction between ions; higher values enhance ionization.

Ostwald’s Dilution Law

For weak electrolytes, α ∝ √(1/C); degree of ionization increases with dilution.

Common-Ion Effect

Suppression of the ionization of a weak electrolyte by the presence of a strong electrolyte having an ion in common with it.

Ionic Product of Water (Kw)

The constant product of [H⁺] and [OH⁻] in water; Kw = 1.0 × 10⁻¹⁴ mol² dm⁻⁶ at 25 °C.

Neutral Solution

An aqueous solution in which [H⁺] = [OH⁻] = 1 × 10⁻⁷ M; pH = 7 at 25 °C.

Acidic Solution

A solution where [H⁺] > 1 × 10⁻⁷ M and pH < 7.

Basic (Alkaline) Solution

A solution where [OH⁻] > 1 × 10⁻⁷ M and pH > 7.

pH Scale

A logarithmic scale expressing acidity: pH = –log [H⁺].

pOH

The negative logarithm of hydroxide-ion concentration; pH + pOH = 14 at 25 °C.

Dissociation Constant (Ka)

Equilibrium constant for the ionization of a weak acid: Ka = [H⁺][A⁻]/[HA].

Dissociation Constant (Kb)

Equilibrium constant for the ionization of a weak base: Kb = [B⁺][OH⁻]/[BOH].

Buffer Solution

A solution containing a weak acid and its conjugate base or a weak base and its conjugate acid that resists pH change on addition of small amounts of acid or base.

Acidic Buffer

Buffer with pH < 7, usually a weak acid plus its salt with a strong base (e.g., CH₃COOH/CH₃COONa).

Basic (Alkaline) Buffer

Buffer with pH > 7, composed of a weak base plus its salt with a strong acid (e.g., NH₄OH/NH₄Cl).

Buffer Action

The process by which added H⁺ is consumed by the conjugate base or added OH⁻ is consumed by the weak acid, limiting pH change.

Salt Hydrolysis

Reaction of cations or anions of a dissolved salt with water to produce the parent acid or base, altering the pH of the solution.

Hydrolysis Constant (Kh)

Equilibrium constant for the hydrolysis of a salt; relates to Ka, Kb, and Kw depending on salt type.

Degree of Hydrolysis (h)

Fraction of the total salt that undergoes hydrolysis at equilibrium.

Solubility

Maximum amount of a solute that can dissolve in a solvent at a given temperature to form a saturated solution.

Sparingly Soluble Salt

An ionic compound whose solubility is less than 0.01 M in water.

Solubility Product (Ksp)

For a saturated solution of a sparingly soluble salt, the product of ion concentrations each raised to the power of its stoichiometric coefficient.

Molar Solubility (s)

Number of moles of a sparingly soluble salt that dissolve per litre of solution; related to Ksp (e.g., for AgCl, s = √Ksp).

Ionic Product

The actual product [cation]ᵃ[anion]ᵇ in a given solution; compared with Ksp to predict precipitation.

Salting Out

Precipitation of a dissolved salt (or soap) by adding another salt that shares a common ion, increasing the ionic product beyond Ksp.

Le Chatelier’s Principle

When a dynamic equilibrium is disturbed, the system adjusts to minimize the disturbance.

Infinite Dilution

Hypothetical state where ion interactions vanish; degree of ionization of even weak electrolytes approaches 1.

Law of Chemical Equilibrium

At equilibrium, the ratio of product activities to reactant activities is constant at a given temperature.

Hydrolysis of Salt of Weak Acid & Strong Base

Generates alkaline solution; Kh = Kw/Ka and pH > 7 (e.g., CH₃COONa).

Hydrolysis of Salt of Weak Base & Strong Acid

Generates acidic solution; Kh = Kw/Kb and pH < 7 (e.g., NH₄Cl).

Hydrolysis of Salt of Weak Acid & Weak Base

May yield neutral, acidic, or basic solution depending on Ka versus Kb; Kh = Kw/(Ka·Kb).

Ostwald Isolation Method

Way to calculate Ka or Kb of weak electrolytes using degree of ionization at known concentration (α² = Ka/C).

Precipitation Prediction Rule

If ionic product > Ksp, precipitation occurs; if < Ksp, the solution remains unsaturated.

Group Analysis (Qualitative)

Use of controlled ion concentration and Ksp differences to precipitate specific cation groups during inorganic analysis.

Dielectric Constant Effect

Higher dielectric constant solvents better separate opposite charges, increasing electrolyte ionization.