Properties of Acids and Bases
Acids bases properties and definition based on Arrhenius theory for learning chemistry suggested that acid dissociate hydrogen ion whereas base hydroxyl ion in water or aqueous solution. But due to limitations, we can not explain acids and bases properties or the nature of acidic and basic neutralization reaction by only one theory. For example, sulfuric acid, nitric acid, and hydrogen chloride molecule show acid properties only when it dissolved in water solution but if we use organic solutions like benzene or alcohol or gases, it does not consider as an acid according to Arrhenius. But acids and bases are the following common properties for the general study of chemistry.
Acids are the chemical elements or substances whose aqueous solution is sour in nature and properties to turns blue litmus to red. Bases are substances whose aqueous solution is slippery in properties, bitter taste. It also has properties to change the color of the litmus to blue and reacts with acids to form salts.
Modern ideas about acid bases properties based on electronic configuration very useful for describing the acid base reaction. Therefore, five theories very useful in describing the properties, redox reactions of acids bases. These theories are, Arrhenius, solvent system concept, Lewis valence orbital theory, hard soft acid base theory. pH scale also plays an important role in defining acidic and basic properties.
Properties of Arrhenius Acid and Base
Arrhenius defines acids bases properties in water solution only. According to his definitions, an acid when dissolved in water, dissociate hydrogen ions and anions. But a base when dissolved in water dissociates into hydroxyl ions and cations. Therefore, acids bases neutralization reaction has properties to the formation of the water molecules.
HCl → H+ + Cl–
NaOH → Na+ + OH–
H+ + OH+ ⇆ H2O
Neutralization Reaction of Acid and Base
Acids and bases reactions in chemistry are highly useful in explaining the acid base neutralization properties in solution. When a strong acid HA reacts with strong base BOH in the chemical solution, all are completely dissociating.
H+ + A– + B+ + OH– ⇆ B+ + A– + H2O
when the above equation balancing by likes ions
H+ + OH– ⇆ H2O
Properties of Strong Acids Bases
The heat of neutralization is the heat change associated with the neutralization of 1-gm equivalent acid by alkali in their very dilute solution. Dilute concentration is used in order to avoid any heat change due to the mixing of acid and base. Neutralization is a chemical equilibrium reaction and exothermic reaction. The heat of neutralization of strong acid and strong base is found to constant unit equal to 13.6 kcal at 25°C temperature.
Since the neutralization of all strong acids and bases properties to the formation of 1-mole water (molecular weight of water = 18 gm mol-1) and thermodynamics enthalpy change (ΔH) will also be the same. Hence the specific heat release during neutralization HCl, HClO4, HNO3, HBr, HI, and H2SO4 (produces acid rain) and strong base NaOH, KOH, RbOH, and Ca(OH)2), namely 13.6 kcal/mole or 56 KJ/mole.
Limitations of Arrhenius Acid and Base
According to Arrhenius’s definitions, HCl is regarded as an acid when dissolved in water. But if we use an organic solvent like ethyl alcohol or acetic acid or gases, HCl does not consider as an acid. Arrhenius limitations cannot account for the properties of acids bases reactions in non-aqueous solvents. For example, NH4NO3 or boric acid in liquid ammonia is an acid, though it does not give H+ ions.
The neutralization examples of acid-base are limited to those reactions which can occur in aqueous solutions only. Therefore, the redox reaction where oxidation number changes by loss or gain by electron particles can not explain by this theory. This theory cannot explain the acid properties of metallic elements present in the periodic table.
Acids Bases Properties in Water and Ammonia
Water solution has both acidic and basic properties and it dissociates H+ and OH– ions. But H+ ion readily polarization by other anion or molecule which exists in the solution. Therefore, according to solvent chemistry, all those polar compounds have properties to give H3O+ ions in H2O will act as acids and all those compounds which can give OH– ions in H2O will act as bases.
Ammonia (NH3) dissociates into two oppositely charged ions like NH4+ and NH2–. Therefore, all those polar compounds that have properties to give NH4+ ions in liquid ammonia will act as acids. But all those compounds which can give NH2– ions in liquid ammonia has properties of bases.
Solvent System Concepts of Acids and Bases
The protonic definition of acids and bases given by Bronsted can be extended to the chemical properties occurring in non-aqueous solvents containing the hydrogen atom. Therefore acids and bases properties of ammonia, hydrogen fluoride, hydrogen peroxide, acetic acid, organic alcohol, etc can easily explain by this theory. An acid is a substance which by dissociation in solution to form the same cation as does the solvent itself due to auto-ionization. A base is one that, gives on dissociation in the solvent the same anion as does the solvent itself on its ionization.
Example of Neutralization Reaction
Just as with the Arrhenius acid base properties, neutralization reaction produces salt and solvent. Some examples of neutralization reaction of acids bases are,
NH4Cl + KNH2 ⇆ KCl + NH3
SOBr2 + K2SO3 ⇆ 2KBr + 2SO2
NOCl + AgNO3 ⇆ AgCl + N2O4
HBr + KOH ⇆ KBr + H2O
Limitations of Solvent Theory
This theory does not consider the number of acids and bases properties and reactions which included in the proton affinity of acid. The acidic and basic nature of the solution can be explained by this theory. Therefore, the acids and bases properties of the atom, ion, or molecule in the solid or gaseous state do not explain by this theory. It can not explain the neutralization reactions and chemical bonding properties of acids and bases occurring without the presence of ions. Therefore, this theory is simply said to be an extension of the Arrhenius water-ion concept.