Bases

Bases are substances that donate a pair of their valence electrons so that a bond can be formed. They are in nature chemically opposite to acids.

Meaning of a base

A base can be defined as a chemical substance that accepts protons, donates its electrons, or leads to the release of the hydroxide ions (OH–) when added to an aqueous solution. It displays the ability to enter into another atom’s valence shell and accept an electron pair bond.

A base displays several properties that can be used to identify them from other chemical substances.

• They may appear slippery on touch, may have a bitter taste, form salts on reaction with acids, and act as catalysts to certain reactions.
• Not all elements have atoms with the ability to provide a molecule with basic properties.
• Bases vary considerably from acids in that they can accept rather than release hydrogen ions.
• The higher the concentration of free hydrogen in a solution, the more acidic it is and the lower its pH value. 

Definition of base

Bases can be explained and defined in three ways:

• Arrhenius’s Theory of bases
• Bronsted-Lowry base
• Lewis base  

Arrhenius’s theory of Bases

• According to Svante August Arrhenius, a Swedish scientist, bases are substances that when dissolved in water, increase their OH– ion concentration.
• One of this theory’s strengths is that it is successful in explaining the reaction between acids and bases that results in salts and water.
• One significant limitation of the Arrhenius definitions of acids and bases is that they do not explain how substances lacking hydroxide ions, such as NO2– and F–, form basic solutions when dissolved in water.

Bronsted-Lowry base

• The Bronsted-Lowry theory defines a base as an acceptor of a proton or as an H+ ion acceptor).
• Bronsted bases accept protons from water (the solvent) to form hydroxide ions.
• One significant limitation of this theory is that it is unable to explain how compounds that lack hydrogens, such as BF3 and AlCl3, exhibit acidic properties.

Lewis Base

• A Lewis base is defined as a substance that has a single electron and can thus act as an electron-pair donor.
• In its definition of acids and bases, this theory does not include the hydrogen atom.
• Nucleophilicity is a property of Lewis bases.
• This concept provides little information about the acid and base strength.
• One of the theory’s drawbacks is that it does not explain acid-base reactions that do not result in the formation of a coordinate covalent bond.

Characteristics and properties of bases

Base compounds display the following characteristics:

• Aqueous base solutions dissociate into ions that conduct electricity.
• Concentrated and strong bases are caustic in nature and react violently with acids and organic matter.
• With pH indicators, bases react in predictable ways. Litmus paper becomes blue, methyl orange becomes yellow, and phenolphthalein becomes pink when exposed to a base. 
• In the presence of a base, bromothymol blue stays blue.
• The pH of a basic solution exceeds 7.
• Base compounds are bitter in taste and have a soapy texture.
• Base compounds conduct electricity when they are dissolved in liquid.
• OH- ions are released when base compounds are dissolved in water.

Strength of a base

Like acids, bases can also be differentiated on their degree of dissociation in water and their reaction to it.

There are two types of bases:

• Strong bases
• Weak bases

A strong base is a compound that can remove a proton (H+) from a very weak acid or completely dissociates it into its ions in water. Sodium hydroxide (NaOH) and potassium hydroxide are two examples of strong bases (KOH).

A weak base is a compound that does not completely dissolve or only dissociate to a very minimal concentration. A weak base dissociates partially in water. Its aqueous solution contains both the weak base and its conjugate acid. An example of a weak base is NH4OH.

Conclusion

The term ‘base’ has been defined in a variety of ways, depending upon its properties. When ionized, bases produce hydroxide ions, according to Arrhenius. According to Lowry-explanation, an acid donates a proton and a base accepts the protons.