Determination of Ionisation and the Constant of Acid and Bases

Acidic substances are characterized by a sour flavor. A molecule that can contribute an H+ ion is called acid. While also remaining energetically favorable after losing that ion. Blue litmus paper is known to convert to red when exposed to acids.

Bases have a bitter taste. The term “alkali ” refers to a base that can be dissolved in water. Salts will be formed when these basic compounds react chemically with acids. It’s common for bases to convert red litmus to blue.

Acids and Bases

The terms acid and base have been discussed in multiple theories and ways, depending on how the qualities of acidity and basicity are seen. Arrhenius, firstly described acids and bases as chemicals which ionize to convert to hydrogen ions and hydroxide ions, respectively. An acid is any substance that can donate a proton, while a base is a proton acceptor, according to the Lowry-Bronsted definition.

Acids are molecules that can coordinate and form complex with unshared electron pairs, and bases are molecules or ions that have unshared electron pairs which are to be shared with acids, according to the Lewis definition. The  molecule must be electron deficient to be acidic in the Lewis sense. The most basic acid-base notion is this. Lowry-Bronsted acids are all Lewis acids, but the Lewis definition also covers boron trifluoride, aluminum chloride, and other reagents.

1. Characteristics of acids

• Acids are naturally corrosive.

• They are excellent electrical conductors.

• The pH of their urine is always less than 7.

• These chemicals produce hydrogen gas when they react with metals.

• Sulfuric acid [H2SO4], hydrochloric acid [HCl], and acetic acid [CH3COOH] are among examples.

2. Characteristics of bases

• When they are touched, they have a soapy texture.

• The Bases are the good conductors of electricity when it’s  in their aqueous solutions .

• The pH values associated with bases are always higher than 7.

• Bases are bitter-tasting chemicals that can turn red litmus paper blue when exposed to them.

• Sodium hydroxide [NaOH], milk of magnesia [Mg(OH)2], and calcium hydroxide [Ca(OH)2] are other examples.

Acid and Base Ionization Constant

The magnitude of an ionization reaction’s equilibrium constant are known to be used to calculate the relative strengths of acids and bases. For example, if HA is the parent acid and A is its conjugate base, the standard equation for ionization of a weak acid in water is:

HA(aq)+H2O(l) ⇌ H3O+(aq)+A-(aq)

This dissociation’s equilibrium constant is as follows:

Ka=[H3O+][A−]/[H2O][HA]

Hydroxide ion is formed when the weak bases react with water, as stated in the general equation below, where B is the parent base and BH+ is its conjugate acid:

B(aq)+H2O(l) ⇌ BH+(aq)+OH-(aq)

And the base ionization constant (Kb), also known as the base dissociation constant, is the equilibrium constant for this reaction:

Kb=[BH+]/[OH−][B]

Water does not appear in the equilibrium constant statement since its activity is 1, once again. The stronger the base and the greater the OH concentration at equilibrium, the larger the Kb.

The magnitude of Ka for the acid and Kb for its conjugate base have a straightforward connection. Consider the ionization of (HCN) in water, which results in an acidic solution formation, and the reaction of CN with water, which results in a basic solution formation:

HCN(aq) ⇌ H+(aq)+CN−(aq)

CN−(aq)+H2O(l) ⇌ OH−(aq)+HCN(aq)

The equilibrium constant expression for HCN ionization is expressed as:

Ka=[H+][CN−]/[HCN]

The equivalent formulation for the reaction of cyanide with water is as:

Kb=[OH−][HCN][CN−]

In this scenario, the equation for water auto-ionization is the total of the processes given by Ka and Kb, and the product of the two equilibrium constants is Kw:

Ka*Kb=Kw

We can calculate the other equilibrium constant for any type of conjugate acid–base pair if we know either of the Ka for an acid or Kb for its corresponding base.

Strength of Acid and Base

 The concept of ionization and dissociation are not the same for all the acids and bases. As a result, acids and bases cannot equally produce H+ and OH- ions in solution. The words “strong” and “weak” describe the strength of an acid or base. The ability of acidic and basic solutions to conduct electricity is described by the strength-strong and weak. The strong acid or the base if the acid or base conducts electricity well. It is a weak acidic or basic substance if it conducts electricity only weakly.

CONCLUSION-

With the completion of study of this article we can understand the relationship between the magnitude of Ka, Kb, pKa, and pKb and the acid or basic strength. And grasp the concept of the leveling effect.