Introduction to Bases
Did you know that the soap you use is a base? Most of the vegetables and fruits that we eat are basic. Those fruits and vegetables have an alkaline effect on your body when consumed.
What are the Bases?
Bases are substances that are slippery to touch when in an aqueous form. They taste bitter and change the colour of a red litmus paper to blue. Like acids, bases also dissociate in the water, but instead of producing H+ ions, they produce OH- ions, i.e. hydroxyl ion. When a base dissolved in water, it is called an Alkali. Calcium hydroxide, Ammonium hydroxide are some of the examples of alkalis. Alkalines become less alkaline when mixed with the acids. The pH level of bases is greater than 7 and ranges from 8-14.
Some examples are sodium hydroxide or caustic soda, limewater or calcium hydroxide. A lot of soaps, detergents, bleaches, kinds of toothpaste, etc. are bases.
Base Definition in Chemistry
Chemistry Glossary Definition of Base
A base is a chemical species that donates electrons and/or accepts protons or releases hydroxide (OH-) ions in an aqueous solution. Bases display specific properties that can be used to help identify them. Bases tend to be slippery when touched (e.g., soap), can taste bitter, react with acids to form salts, and catalyze specific reactions. Different types of bases include Lewis base, Bronsted-Lowry base, and Arrhenius base. Examples of bases include alkaline earth metal hydroxides, soap and alkali metal hydroxides.
Key Takeaways: Base Definition
- A base is a substance that reacts with an acid in an acid-base reaction.
- The mechanism through which a base works has been argued throughout history. Generally, a base either accepts a proton, releases a hydroxide anion when dissolved in water, or donates an electron.
- Examples of bases include hydroxides and soap.
The word “base” came into use in 1717 by French chemist Louis Lémery. Lémery used the word as a synonym for Paracelsus’ alchemical concept of a “matrix” in alchemy. Paracelsus proposed natural salts grew as a result of a universal acid mixing with a matrix.
While Lémery may have used the word “base” first, its modern usage is generally attributed to French chemist Guillaume-François Rouelle. Rouelle defined a neutral salt as the product of the union of an acid with another substance that acted as a “base” for the salt. Examples of Rouelle’s bases included alkalis, metals, oils, or absorbent earth. In the 18th century, salts were solid crystals, while acids were liquids. So, it made sense to early chemists that the material that neutralized the acid somehow destroyed its “spirit” and allowed it to take solid form.
Properties of Bases
Some of their properties are
A base will usually taste bitter.
A Base will turn red litmus to blue.
The pH level of a base is from 8 to 14.
Bases react with acid to form salt and water.
Classification of Bases
They are usually classified based on strength, concentration and acidity.
Classification based on the strength
Just like acids, the strength of bases depends on the number of hydroxyl ions it produces when dissolved in water. A high amount of hydroxyl ion represents a strong base, and a low amount of base represents a weak base.
Strong base: A base that dissolves entirely or almost entirely in water is known as a strong base. E.g. NaOH, KOH, Ca(OH)2, etc.
Weak base: A base which doesn’t dissolve completely is called a weak base. E.g. Ma(OH)2, NH4OH
Classification based on the concentration
The concentration of the base depends upon the amount of base dissolved in water. It is of two types, i.e. Concentrated and Dilute base.
Concentrated Base: An aqueous solution which has a relatively high percentage of the base is a concentrated base. E.g. Concentrated sodium hydroxide, concentrated potassium hydroxide, concentrated ammonium hydroxide, etc
Diluted Base: An aqueous solution which has a relatively low percentage of the base is a dilute base. E.g. dilute sodium hydroxide, dilute potassium hydroxide, dilute ammonium hydroxide, etc.
Classification based on the Acidity of the Base.
The acidity of a base depends upon the number of hydroxyl ions it has. The acidity also depends on the number of hydrogen ions with which a base can combine as one hydrogen ion combines with one hydroxyl ion. It is usually of 3 types, namely: Triacidic base Diacidic base, and Monoacidic base.
Triacidic base: This base has three hydroxyl ions and combines with three hydrogen ions. E.g. Aluminium Hydroxide.
Diacidic base: This base contains two hydroxyl ions and combines with two hydrogen ions. For e.g. Fe(OH)2, Zn(OH)2, Mg(OH)2, etc.
Monoacidic base: This base consists only one hydroxyl ion and only combines with one hydrogen ion. E.g. NaOH, KOH, NH4OH, etc
Types of Bases
Bases can be categorized according to their degree of dissociation in water and their reactivity.
- A strong base dissociates entirely into its ions in water or is a compound that can remove a proton (H+) from a weak acid. Examples of strong bases include potassium hydroxide (KOH) and sodium hydroxide (NaOH).
- A weak base incompletely dissociates in water. Its aqueous solution includes both the conjugate acid and its weak base.
- A neutral base is one which forms a bond with a neutral acid such that the acid and base share an electron pair from the base.
- A solid base is active in the solid form. Examples include NaOH mounted on alumina and silicon dioxide (SiO2). Solid bases may be used in anion exchange resins or for reactions with gaseous acids.
- A superbase is even better at deprotonation than a strong base. These bases have very weak conjugate acids. Such bases are formed by mixing its conjugate with an alkali metal. A superbase cannot remain in aqueous solution because it is a stronger base than the hydroxide ion. An example of a superbase is sodium hydride (NaH). The strongest superbase is the ortho-diethynylbenzene dianion (C6H4(C2)2)2−.