There are different definitions for the base. But the one definition that is common in all three definitions is bases react with acid to form a neutral compound or salts and water. And is given by G.-F. Rouelle. It is the ion that is present in this compound that makes it a characteristic property. Arrhenius proposed that the presence of hydroxyl ion, $\mathrm{OH^{-}}$ leads to the characteristic property of a base. According to Bronsted Lowry's theory of bases, a base is a substance that can accept protons or Hydrogen ions, $\mathrm{H^{+}}$. And in lewis's base theory base is a compound that can donate the electron pair present on them.
The termbase means any substance that when dissolved in water is slippery, bitter taste, and can turn red litmus paper to blue. And can react with acids to form a neutral compound, salt, and water as byproducts. The compounds sodium hydroxide and ammonia are bases. They are ionic compounds that contain two types of ions they are positively charged metal ions and negatively charged non-metal ions. They are joined together by an ionic bond. Upon dissolution in water involves the dissociation of this ionic bond. If the pH of a basic solution is above 7, the value varies with its strength.
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The first definition for bases was given by Arrhenius in the year 1884. So according to this theory of base, a base is an ionic compound that when dissolved in water undergoes dissociation to produce hydroxyl ions or $\mathrm{OH^{-}}$ ions. Or it is the species that increases the concentration of $\mathrm{OH^{-}}$ ions in the solution form. The dissociation of this ionic compound produces a negatively charged species called hydroxyl ion and a positively charged ion that is metallic. For example Sodium hydroxide, $\mathrm{NaOH}$ is an Arrhenius base. The dissociation is,
$$\mathrm{NaOH(aq)\to Na^{+}(aq)+OH^{-}(aq)}$$
Calcium hydroxide, $\mathrm{Ca(OH)_{2}}$ is also a base that contains two hydroxyl ions. The dissociation is,
$$\mathrm{Ca(OH)_{2}(aq) \to Ca^{2+}(aq)+2\:OH^{-}(aq)}$$
These compounds react with an acid to form the corresponding salt too. Sodium hydroxide reacts with the acid Hydrogen chloride to form the salt Sodium chloride and water. The reaction is,
$$\mathrm{2\:HCl+NaOH\to NaCl+H_{2}O}$$
This reaction is called neutralization reaction as it involves the formation of respective salt and water and they are neutralizing the property of each other.
Bronsted Lowry treats acid and base based on their Hydrogen ion acceptance or donation nature. So a Bronsted base is a chemical species that accept Hydrogen ion, H+ towards it. While acid is something that can donate hydrogen ions. As they are accepting a positively charged ion so it must contain at least one electron pair as lone pair. So from the Bronsted theory, the Ammonia base can react with the acid, and Hydrogen chloride $\mathrm{HCl}$ leads to the acceptance of proton from $\mathrm{HCl}$ towards it. And the reaction is,
This is due to the presence of lone pair of electrons in the Ammonia molecule. In which the proton present in the Hydrogen chloride is transferred from $\mathrm{HCl}$ to the Ammonia molecule. And the product of this reaction is also a salt formed by the neutralization reaction of an acid and the base. From the Arrhenius theory point of view, the compound Ammonia is not a base.
Lewis's theory of base is a theory proposed by the scientist G.N. Lewis in 1923. This theory has overcome the difficulties obtained by the Bronsted theory. As it only focuses on the proton acceptor and donor concept. Instead, Lewis's theory aims for electron transfer. So according to this theory, Lewis's bases are compounds that can donate electron pairs. So the compound must contain at least one lone pair of electrons. While acid is a species that accepts the electron pair donated by the base. The neutralization reaction of a lewis base Methyl Amine, $\mathrm{CH_{3}NH_{2}}$ with the acid Hydrogen chloride, $\mathrm{HCl}$ is shown below.
Bases can be categorized into different types depending on the number of hydroxyl groups, and the strength of the base. The classification of bases based on the number of Hydroxyl groups is based on the Arrhenius concept and is of three types. They are discussed in detail below.
Mono acid-base - The base that contains only one Hydroxyl group, $\mathrm{OH^{-}}$ is mono acid-base. They can only combine with one hydrogen atom. An example of such a base is Potassium hydroxide, $\mathrm{KOH}$.
Diacidic base - As the name itself tells it is a base that contains two hydroxyl ions. And can combine with two hydrogen atoms. An example is Calcium hydroxide, $\mathrm{Ca(OH)_{2}}$.
Triacidic base - As the name itself tells it contains three Hydroxyl groups. And can combine with the three hydrogen atoms of acids. An example is Aluminum hydroxide, $\mathrm{Al(OH)_{3}}$.
The classification based on the strength of bases or their degree of ionization to produce corresponding ions faster are,
Strong base - The bases that can dissociate completely to their respective ions or are having a high degree of ionization are strong. The pH of such bases is in between the range of 13-14. Sodium hydroxide is a strong base.
Weak base - The base in which the degree of dissociation is low is weak bases. Or it cannot be dissociated from respective ions. The pH of such bases is a low value compared to strong bases that are in the range of 7-10. Ammonium hydroxide, $\mathrm{NH_{4}OH}$ is a weak base.
Alkalies are the ionic compound formed by the alkali metal or alkaline earth metals. They are also a type of base that can dissolve in water. All the alkali are basic but not all the bases are alkaline. This means that base cannot be dissolved in water to form a solution. While alkalies dissolve in water to produce a basic solution having a pH greater than 7. Some of the important alkalies are Sodium hydroxide, Aluminum hydroxide, Lithium carbonate, etc.
Some of the physical properties of bases are discussed below.
Bases are soapy.
They contain a bitter taste.
Bases can turn the red litmus paper to blue.
They should not be touched by hand as they are very corrosive to the skin.
They form salts when contacted with acid compounds.
All the basic compounds contain one lone pair of electrons at the least. Some of the examples of bases are given below.
$\mathrm{NaOH}$( Sodium hydroxide)
$\mathrm{KOH}$ (Potassium hydroxide)
$\mathrm{LiOH}$ (Lithium hydroxide)
$\mathrm{Al(OH)_{3}}$(Aluminum hydroxide)
$\mathrm{NH_{3}}$ (Ammonia)
$\mathrm{CsOH}$ (Cesium hydroxide)
Bases are important compounds with a pH greater than 7. And can react with acidic compounds to produce salts. There are three different classifications for bases they are Arrhenius, Lewis, and Bronsted theory. Among three theories all mention the reaction of a base with acids to form corresponding salts. Bases are classified into monoacidic basic, acidic base, and triacidic base. And is based on the number of hydroxyl groups. Another classification of the base is there which is based on the degree of dissociation of bases. Alkalies are a type of base that dissolves in water while bases do not. And all the alkali are basic. Bases are soapy and have a bitter taste. Sodium hydroxide, Ammonia, etc. are examples of bases.
Q1. What is the example of household bases?
Ans. Some of the commonly used household bases are Soap, baking powder, toothpaste, washing powder, bleach, etc.
Q2. Is milk a base?
Ans. No, milk is not a base. It is an acidic substance as it contains acid lactic acid. And the pH of milk is in the range of 6-7.
Q3. What are the uses of bases?
Ans.
Bases are used extensively in the manufacturing of soaps and detergents.
Antacid contains the base.
Used in alkaline batteries.
Main components in the drain and oven cleaners.
In the pharmaceutical industry.
Q4. Is blood basic?
Ans. Blood has a pH value in the range of 7.35-7.45. Any compound with a pH higher than 7 is basic. So blood is a base. And is also an example of the basic buffer.
Q5. Is honey alkaline?
Ans. Honey is an acid compound, not an alkaline compound. The pH of honey is so low that can then prevent the growth of microorganisms.
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