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The Concepts of ionization and dissociation are not the same for all acids and bases. As a result, acids and bases are not all equal in their ability to produce H+ and OH- ions in solution. The phrases “strong” and “weak” describe the strength of an acid or base, respectively. The capacity of acidic and basic solutions to conduct electricity is described by the phrases strong and weak. It’s a strong acid or base if the acid or base conducts electricity. It will be a weak acid or weak base if it conducts electricity weakly.
Principle of acids and bases
Like many other chemical theories, the idea of acids and bases has undergone multiple revisions in recent years. The revisions have always been made to make the theory more generic. The following are the three most popular theories today:
Arrhenius Theory
Svante Arrhenius, a Swedish chemist, introduced two distinct classifications of substances in 1884: acids and bases. Certain ions were released into the solution when it was dissolved in an aqueous solution.
When introduced to water, acid raises the concentration of H+ ions. When hydrogen ions mix with water molecules, they generate the hydronium ion (H3O+). The addition of H2O to the reactants side of the chemical equation represents this process.
HCl(aq) → H+(aq)+Cl–(aq)
When hydrochloric acid (HCl) is dissolved in water, it dissociates entirely into hydrogen (H+) and chlorine (Cl-) ions, releasing H+ ions into solution. The hydronium ion equation is formed as follows:
HCl(aq)+H2O(l) → H3O+(aq)+Cl–(aq)
When added to water, a base raises the concentration of OH- ions present. The following equation represents the dissociation:
NaOH(aq) → Na+(aq)+OH–(aq)
When sodium hydroxide (NaOH) is dissolved in water, it dissociates into sodium (Na+) and hydroxide (OH-) ions, releasing OH- ions into solution.
Bronsted Lowry Theory
In 1923, scientists Johannes Nicolaus Bronsted and Thomas Martin Lowry separately defined acids and bases based on their ability to donate or receive protons (H+ ions). Acids are defined as proton givers in this theory, while bases are defined as proton acceptors.
Amphoteric refers to a chemical that functions as both a Bronsted-Lowry acid and a base. This extended the Arrhenius definition by removing the requirement that a substance be made entirely of hydrogen (H+) or hydroxide (OH-) ions to be categorized as an acid or basic.
Consider the chemical equation below.
HCl(aq)+NH3(aq) → NH4+(aq)+Cl–(aq)
Hydrochloric acid (HCl) “gives” a proton (H+) to ammonia (NH3), which “accepts” it, resulting in the formation of a positively charged ammonium ion (NH4+) and a negatively charged chloride ion (Cl-). As a result, HCl is a Bronsted-Lowry acid (it contributes a proton), whereas ammonia is a Bronsted-Lowry base (it accepts a proton) (accepts a proton).
Cl– is also referred to as the conjugate base of the acid HCl, while NH4+ is referred to as the conjugate acid of the base NH3.
Lewis Theory
Acids act as electron-pair acceptors, while bases act as electron-pair donors, according to the Lewis theory of acids and bases. In contrast to the previous definitions, this one does not include the hydrogen atom at all. It simply refers to the exchange of electron pairs.
Strength of acids and bases-
Acid and base strength is determined by how much acid or base ionizes in solution. In a solution, a strong acid or base gets totally ionized. An acid and a base react with each other to form a salt in a neutralization reaction. Salt is an ionic substance in which the cation will be base and the anion will be acid.
Dissociation constants are commonly referred to as pKa and pKb in chemistry. The acid dissociation constant is pKa, and the base dissociation constant is pKb. These words are used to make working with extremely big or extremely small quantities easier. The letter “p” stands for “negative logarithm” in these words. pKa is the negative logarithm of Ka, while pKb is the negative logarithm of Kb.
The negative logarithm of Ka is pKa. The acid dissociation constant of a solution is called Ka. It’s a way of calculating how strong an acid is in a given solution. Acids are a type of chemical that can release one or more hydrogen ions (protons) into a solution. If the acid dissociation constant, Ka, is greater, the acid has been totally (or nearly completely) decomposed into ions, resulting in hydrogen ions. Then it denotes that the acid is a powerful acid. Strong acid has a lower pKa value since it is the negative logarithmic value of Ka.
pKa = -log10Ka
The negative logarithm of Kb is pKb. The basic dissociation constant is Kb. It is used to quantitatively determine the strength of a base. A basic solution is formed when a base is dissolved in water and dissociates into ions. Strong bases fully dissociate. Weak bases partially dissociate.
pKb = -log10Kb
Weaknesses of acids and bases-
Weak acids arise when the hydrogen atom and the other atom in the bond have insufficient polarity to allow the hydrogen ion to be easily removed. The size of the atom linked to hydrogen is another aspect that influences the acid’s potency.
A weak base is one that does not entirely dissociate in water, leaving only a tiny proportion of hydroxide ions and the concerned basic radical in the ensuing aqueous solution, and a considerable number of undissociated base molecules.
CONCLUSION-
The study of acid and bases helps us understand the nature of the chemical substance present and their strength whether they are strong or weak
