Introduction to Ionization
The ionization of a compound can be explained as a process where a neutral molecule splits into charged ions when exposed to a solution.
Arrhenius theory says that acids are the compounds that are dissociated in an aqueous medium to generate hydrogen ions, H+(aq). On the other side, bases are the compounds that furnish hydroxyl ions, OH−(aq) in an aqueous solution or medium.
Let us look at the difference between ionisation and dissociation.
The primary difference between dissociation and ionization or the is, dissociation is the process of separating the charged particles which already exist in the compound, on the other side, ionization is the formation of new charged particles, which are not present in the previous compound.
Arrhenius theory plays a major role in explaining the ionization of acids and bases because mostly ionization occurs in an aqueous medium. Based on the degree of ionization of acids and bases, we can define the strength of both acids and bases. Also, the degree of ionization differs for different compounds of acidic and basic. A few acids, such as hydrochloric acid (HCl), perchloric acid (HClO4), completely dissociate into their constituent ions in an aqueous medium.
All these acids are referred to as strong acids. Ionization of acids produces hydrogen ions, and therefore, these compounds act as proton donors. In the same way, a few bases such as sodium hydroxide (NaOH), lithium hydroxide (LiOH) too dissociate completely into their ions in an aqueous solution or medium. These bases are referred to as strong bases. The ionization of these bases produces hydroxyl ions (OH−).
Therefore, the ionization degree of acids and bases depends based on the degree of dissociation of compounds into their constituent ions. The strong acids and bases have a high degree of ionization when compared to the ionisation of weak acid and base. Also, a strong acid implies a good proton donor, whereas a strong base implies a good proton acceptor - for example, dissociation of weak acid HA.
HA(aq) + H2O(l) ⇌ H3O + (aq) + A-(aq)
Let us look at the Arrhenius Theory explanation in brief.
This reaction indicates that acid dissociation equilibrium is dynamic in nature, where the transfer of protons can occur in both forward and backward directions. If HA has a higher tendency to donate a proton compared to that of H3O+, HA acts as a strong acid in comparison to the H3O+ ion. Because the stronger acid donates a proton to the stronger base, the equilibrium moves towards the direction of a formation of a weaker acid and base.
Generally, the strong acids have weaker conjugate bases, whereas the strong bases have weaker conjugate acids. This is due to the high degree of ionization of strong acids and bases.
Ionization of a Compound
Bases are the compounds that furnish the hydroxyl ions and OH– present in the aqueous medium. The degree of ionization of both acids and bases helps to determine its strength. Based on different acidic and basic compounds, the degree of ionization can differ.
Ionization of Acids and Bases
Ionization of Acids
The Ionisation degree refers to the strength of either an acid or a base. A strong acid is said to ionize in water completely, whereas a weak acid is said to ionise only partially. Because there are various degrees of acid’s ionization, there also exists various levels of weakness, where there exists a simple quantitative way to express.
Since the weak acid ionization is an equilibrium, the equilibrium constant expression and the chemical equation can be stated as follows:
HA(aq) + H2O(l) ⇌ H3O + (aq) + A-
Ka = [H3O+] [A–] / [HA]
An equilibrium constant for the ionisation of an acid describes its Acid Ionisation Constant (Ka). However, the stronger the acid, the acid ionisation constant (Ka) will be the larger. It means that a strong acid is a donor of a better proton. Because of the result of the product concentration in the numerator of the ionization constant (Ka), the stronger the acid, the larger is the acid Ka.
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Ionization of Bases or Base Ionization
A few bases such as sodium hydroxide or lithium hydroxide get completely dissociated into their ions in an aqueous solution, which is referred to as the strong bases. Thus, these bases’ ionisation yields hydrochloric ions, as (OH–). One of the same expressions for the bases is given as follows:
A + H2O ⇌ OH– + HA+
Kb = [OH–] [HA+] / [A]
The base ionisation constant, that is, Kb, refers to as an equilibrium constant for the ionisation of a base. Thus, we can say that a strong base implies a good proton acceptor, whereas a strong acid implies a good proton donor. The dissociation of either weak acids or weak bases in water can be given as follows.
CH3COOH + H2O CH3COO‾ + H3O+
NH3 + H2O NH4+ (aq) + OH- (aq)
Degree of Ionization
The ionization degree is also called as an ionization yield, which refers to the proportion of neutral particles, like those in aqueous or gaseous solutions, which are ionized to the charged particles. For electrolytes, it could be understood as the capacity of either acid or base to ionize itself. A low ionization degree is at times referred to as a partially or weakly ionized, and as a high degree of ionization as fully ionized. But, a fully ionized degree can also mean that an ion has no electron count left.