PHA266_673ef6d1d2825

Theory of Strong Electrolytes

  • Electrolytes vs. Nonelectrolytes

    • Electrolytes are salts or molecules that completely ionize in solution, enabling conductivity.

    • Nonelectrolytes do not dissociate into ions and do not conduct electricity.

Types of Electrolytes

  • Strong Electrolytes:

    • Strong Acids

    • Strong Bases

    • Salts

  • Weak Electrolytes:

    • Weak Acids

    • Weak Bases

Strong Electrolytes

  • Definition: A strong electrolyte fully or almost fully ionizes or dissociates in a solution, consisting entirely of ions.

Examples of Strong Electrolytes

  • Chemical equations show dissociation of strong electrolytes:

    • Reaction arrow: Strong electrolytes use a one-way arrow (→) indicating complete ionization.

    • General form: strong electrolyte (aq) → cation+ (aq) + anion- (aq)

Strong Electrolyte Example Reactions

  • HCl dissociates completely into H+ and Cl-.

    • HCl (aq) → H+ (aq) + Cl- (aq)

  • H2CO3 (weak acid) does not fully dissociate:

    • H2CO3 (aq) ⇋ H+ (aq) + HCO3- (aq)

Characteristics of Strong Electrolytes

  • They must have high solubility to act as strong electrolytes.

  • Notable examples include: HCl, H2SO4, NaOH, KOH.

Ionization and Chemical Behavior

  • Strong Electrolytes: 100% ionized in solution:

    • NaCl(s) → Na+(aq) + Cl-(aq)

    • HCl(g) → H3O+(aq) + Cl-(aq)

Ionic Activity and Coefficients

  • Activity reflects practical ion interactions and deviations from complete ionization.

  • At high concentrations, ions may form ion pairs (e.g., Na+Cl-) influencing activity.

  • Equation for practical activity coefficient on molal scale: a/m = Ym.

  • Molarity scale example: a = yc * c.

  • Rational activity coefficient for mole fraction: a = yx * X.

Ionic Strength

  • Definition: A measure of the total concentration of ions in a solution, influencing properties like solubility.

  • Equation: μ = ½ Σ cizi²

    • ci: concentration of each ion

    • zi: valence of each ion

Ionic Strength Calculation Examples

  • Example 1: For Na+ (0.1 M) and Cl- (0.2 M):

    • μ = ½ (0.1 * 1² + 0.2 * 1²) = 0.15

  • Example 2: For 0.010 M KCl:

    • μ = ½ (0.01 * 1² + 0.01 * 1²) = 0.01

  • Example 3: For 0.010 M BaSO4:

    • μ = 0.04

  • Example 4: Total μ for KCl + BaSO4 + Na2SO4 = 0.08

Debye-Hückel Theory

  • Equation relates activity coefficients to valence, ionic strength, and solvent properties:

    • Log yi = - A zi² √μ (A varies with temperature and solvent)

  • Factors include ionic strength, valence of ions, nature of solvent, and temperature.

Osmolality

  • Defines the particle concentration in kg of water; influences bioavailability in pharmaceuticals.

  • Calculation: Milliosmolality (mOsm/kg) = i x mm where:

    • i = number of ions formed per molecule,

    • mm = millimolal concentration.

  • Molarity is more commonly used in clinical practice than molality.