Alkali vs Base- Definition, 7 Key Differences, Examples

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Alkali Definition

Alkali is a basic soluble hydroxide of alkali metals or alkaline earth metals. 

  • These are strong bases that share most of the characteristics of bases like the formation of neutral salts with acids and the conversion of red litmus paper into the blue.
  • The term alkali is derived from the Arabic work ‘al qally’ meaning calcined ashes indicating the original source of alkaline substances.
  • Alkalis are generally distinguished from other bases on the basis of their solubility in water.
  • Alkalis can be considered a subset of bases as these are bases that can be dissolved in water to produce OH ions.
  • Most alkalis are water-soluble, but some chemicals like barium carbonate are only soluble in acidic solutions.
  • Different alkalis of industrial importance have been manufactured in industries. The most important ones being soda ash and caustic soda.
  • These are essential in the production of glass, soap, and other chemicals used in textiles and metals.

Alkali vs Base

Image Source: Walkerma and Ondřej Mangl.

Base Definition

The base is a chemical compound that reacts with acids to produce salts. The definition of bases differs in different concepts.

  • According to the Arrhenius concept, bases are substances that dissociate in an aqueous solution to form hydroxide ions.
  • According to the Bronsted-Lowry concept, a base is a compound that can accept hydrogen ions.
  • According to the Lewis concept, a base is a donor that can share a pair of electrons with an electron acceptor.
  • Bases are defined by a group of characteristics that help differentiate them from acids. The pH of these substances is greater than seven, and these turn red litmus paper into blue.
  • The base is a broader category of compounds that consists of alkali as a subset.
  • Bases, except alkali, do not dissolve in water and mostly result in white precipitate in water.
  • Most of the basic compounds are covalent compounds usually formed between metals and non-metals with similar valencies. 

7 Major Differences (Alkali vs Base)

Characteristics Alkali Base
Definition Alkali is a basic soluble hydroxide of alkali metals or alkaline earth metals. The base is a chemical compound that reacts with acids to produce salts.
Solubility Alkalis dissolve in water to produce OH-. Bases do not dissolve in water.
Relation All alkalis are bases. Alkali is a subset of the base. All bases are not alkali.
Reaction with acid Alkali reacts with acids to produce OH- ions and accepts protons. Bases neutralize the acid to form salt and water.
Compounds Alkalis are carbonates and hydroxides of alkali metals. Bases mostly are compounds with a hydroxide group or a lone pair of electrons.
Chemical category Alkali is an ionic compound of Group I metals. Bases can be ionic or covalent of metals from different groups.
Examples Sodium hydroxide and potassium hydroxide are examples of alkali. Zinc hydroxide and copper oxide are examples of bases.

Examples of alkali

Sodium hydroxide (NaOH)

  • Sodium hydroxide is a white solid ionic compound composed of a single sodium and hydroxide ion.
  • Sodium hydroxide (also known as caustic soda) is soluble in water and releases hydroxide ions.
  • It is a strong base that decomposed proteins and might even result in corrosion and burns on the skin.
  • It neutralizes with acid to produce a significant amount of heat, enough to ignite combustible materials.
  • It is used in laboratories and industries as a solid or diluted liquid and is often used to manufacture soaps, paper, and petroleum products.
  • Sodium hydroxide has also been approved by FBA as safe for use as it serves as a pH control agent.

Examples of base

Zinc hydroxide (Zn(OH)2)

  • Zinc hydroxide is a chemical compound consisting of a single zinc atom and two hydroxide radicals with the molecular formula, Zn(OH)2.
  • It can be found naturally in different rocks which are then extracted and purified for industrial purposes.
  • Zinc hydroxide is a base but not an alkali as it is insoluble in water. It is a weaker base and thus, can react with other bases.
  • It does, however, dissolve in strong acids and reacts to form acidic salt and water molecules.
  • It is often used in pharmaceutical products as an adsorbing agent. It also has antiseptic activity.
  • Zinc hydroxide is also used as an intermediate compound for the commercial production of pesticides and pigments.

References and Sources

  • National Center for Biotechnology Information. “PubChem Compound Summary for CID 14798, Sodium hydroxide” PubChem Accessed 17 February 2021.
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About Author

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Anupama Sapkota

Anupama Sapkota has a B.Sc. in Microbiology from St. Xavier’s College, Kathmandu, Nepal. She is particularly interested in studies regarding antibiotic resistance with a focus on drug discovery.

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