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The Arrhenius hypothesis, proposed in 1887 by the Swedish scientist Svante Arrhenius, states that acids dissolve in water to form electrically charged atoms or molecules termed ions, one of which is a hydrogen ion (H+), and that bases ionise in water to form hydroxide ions (OH). The hydrogen ion cannot exist alone in aqueous solution; rather, it coexists with a water molecule as the hydronium ion (H3O+). The hydronium ion is still commonly referred to as the hydrogen ion in practise.
The acidic behaviour of a number of well-known acids (e.g., sulfuric, hydrochloric, nitric, and acetic acids) and the fundamental properties of several well-known hydroxides (e.g., sodium, potassium, and calcium hydroxides) are explained in terms of their ability to produce hydrogen and hydroxide ions in solution, respectively. Additionally, these acids and bases can be classed as strong or weak acids and bases based on the concentration of hydrogen ion or hydroxide ion formed in solution. The reaction between an acid and a base produces salt and water; the latter is formed when a hydrogen ion and a hydroxide ion combine.
Ionization of acids and bases
When a chemical is exposed to a solution, it undergoes ionisation, which is the process by which neutral molecules are broken up into charged ions. Acids, according to Arrhenius’s theory, are compounds that dissociate in water to form hydrogen ions, H+. Due to the fact that the majority of ionisation happens in an aqueous medium, Arrhenius’s theory is critical for understanding acid and basic ionisation. Acids and bases can be classified according to their degree of ionisation. Additionally, the degree of ionisation changes according to the acidity or basicity of the substance. A few acids, such as hydrochloric acid (HCl) and perchloric acid (HClO4), completely dissociate into their constituent ions in aqueous environments.
Explanation of Arrhenius acid and base ionization
This answer demonstrates that the acid dissociation equilibrium is dynamic, with proton transfer occurring in both directions. Due to the fact that HA has a greater inclination to donate protons than H3O+, it behaves strongly acidic in comparison to H3O+. Because the stronger acid contributes a proton to the stronger base. The equilibrium swings in favour of forming a weaker acid and a weaker base. Conjugate bases with strong acids have weaker conjugate bases, and vice versa. This occurs as a result of the high degree of ionisation of strong acids and bases.
Ionization of a Compound
By contrast, bases are the substances that contribute hydroxyl ions, OH–, to the aqueous medium. The degree to which acids and bases are ionised determines their strength. The degree of ionisation varies with the acidity and basicity of the components.
Ionization of Acids
The degree of ionisation is a measure of an acid or base’s acidity or baseness. In water, a strong acid completely ionises, whereas a weak acid just partially ionises. Due to the fact that acids have variable degrees of ionisation, they also have varying degrees of weakness, which may be quantified. Due to the equilibrium nature of the ionisation of a weak acid, the chemical equation and expression for the equilibrium constant are as follows:
HA (aq) + H2O -> H3O+ (aq) + A–
Ka = [H3O+] [A–] / [HA]
The Equilibrium Constant for Ionisation of an Acid is used to define the Acid Ionisation Constant (Ka). The greater the acid ionisation constant, however, the stronger the acid. As a result, a strong acid is a better proton donor than a weak acid. Due to the product’s concentration in the numerator of the Ka constant, the larger the acid ionisation constant, the stronger the acid (Ka).
Ionization of Bases
Certain bases, such as lithium hydroxide or sodium hydroxide, completely dissociate into their ions in aqueous solution and are referred to as strong bases. As a result, ionisation of these bases results in the formation of hydrochloric ions, represented by the symbol (OH–). An equivalent sentence for the bases is:
A + H2O ⇢ OH– + HA+
Kb = [OH–] [HA+] / [A]
The equilibrium constant for base ionisation is denoted by the abbreviation Kb. As a result, a strong base means that it is an excellent proton acceptor, whereas a strong acid implies that it is an excellent proton donor. In water, weak acids and weak bases dissociate as follows:
CH3COOH + H2O ⇔ CH3COO‾ + H3O+
NH3 + H2O ⇔ NH4+ (aq) + OH‾(aq)
Conclusion
Ionization is the process of gaining or losing electrons to give an atom or a molecule a negative or positive charge. An ion is a positively charged atom or molecule. Atoms, molecules, and ions can ionise when they collide with subatomic particles or with electromagnetic radiation, respectively. Ion pairs can be formed through heterolytic bond cleavage and heterolytic substitution. It is possible to ionise a nucleus by transferring its energy to an inner-shell electron.
