Study Notes on Tonic Equilibrium and Electrolyte Chemistry of Electrolytes and Ionic Product of Water

General Principles of Tonic Equilibrium and Electrolytes

  • Definition According to Paraday:

    • According to Paraday, an electrolyte is defined as a substance that acts as a good conductor of electricity when it is in its aqueous form or in its fused (molten) form.

  • Non-Electrolytes:

    • Non-electrolytes are substances that do not conduct electricity in aqueous or molten states.
    • Examples of non-electrolytes include:
      • Glucose
      • Fructose
      • Sucrose
      • Urea

Classification of Electrolytes: Strong vs. Weak

  • Strong Electrolytes:

    • Strong electrolytes are defined as those electrolytes that undergo 100%100\% dissociation at any concentration or dilution.
    • The value of the degree of dissociation, represented by α\alpha, is equal to 11 for strong electrolytes:
      α=1\alpha = 1
    • General categories of strong electrolytes:
      • Inorganic acids
      • Inorganic bases
      • Salts

  • Weak Electrolytes:

    • Weak electrolytes are those substances where the degree of dissociation (α\alpha) increases as the dilution increases.
    • General categories of weak electrolytes:
      • Organic acids
      • Organic bases

Specific Chemical Categorizations of Electrolytes

  • Weak Inorganic Acids:

    • Certain inorganic acids are classified as weak electrolytes, specifically:
      • H2CO3H_2CO_3 (Carbonic acid)
      • H3BO3H_3BO_3 (Boric acid)
      • HCNHCN (Hydrogen cyanide)
      • H2SH_2S (Hydrogen sulfide)

  • Metal Hydroxides (Bases):

    • All dd-block and pp-block metal hydroxides are categorized as weak bases.
    • In contrast, ss-block metal hydroxides are generally strong in nature.
    • Exceptions in the s-block: The following ss-block metal hydroxides are considered weak bases rather than strong:
      • LiOHLiOH
      • Be(OH)2Be(OH)_2
      • Mg(OH)2Mg(OH)_2

Ionic Product of Water

  • Dissociation Reactions of Water:

    • The process can be represented by the auto-ionization of two water molecules:     H2O+H2O⇌H3O++OH−H_2O + H_2O \rightleftharpoons H_3O^+ + OH^-
    • Alternatively, it can be expressed in a simplified form as:     H2O⇌H++OH−H_2O \rightleftharpoons H^+ + OH^-

  • Constants for Water:

    • KiK_i is the ionisation constant of water.
    • KwK_w is the ionic product of H2OH_2O.

  • Mathematical Formulations:

    • The ionisation constant is defined by the ratio of the product of the concentrations of the ions to the concentration of the undissociated water:     Ki=[H+][OH−][H2O]K_i = \frac{[H^+][OH^-]}{[H_2O]}
    • The ionic product of water (KwK_w) is related to the ionisation constant by the following derivation:     Kw=Ki×[H2O]=[H+][OH−]K_w = K_i \times [H_2O] = [H^+][OH^-]
    • Therefore, the final expression for the ionic product is:     Kw=[H+][OH−]K_w = [H^+][OH^-]

  • Concentration of Water ([H2O][H_2O]):

    • The concentration of pure water is calculated based on its density (approximately 1000 g/dm31000\,g/dm^3) divided by its molar mass (18 g/mol18\,g/mol):     [H2O]=100018≈55.55 mol dm−3[H_2O] = \frac{1000}{18} \approx 55.55\,mol\,dm^{-3}