Hard soaps (), also termed soda soaps in older terminology, are categorized under

soap Soap is a salt (chemistry), salt of a fatty acid (sometimes other carboxylic acids) used for cleaning and lubricating products as well as other applications. In a domestic setting, soaps, specifically "toilet soaps", are surfactants usually u ...

s and are typically sodium salts of

fatty acids In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...

. They vary in color from white to brownish and have a fatty acid content ranging from 72 to 75%. These soaps are typically made from lower-quality fats. Hard soaps serve as the foundation for products frequently labeled as fine soaps, which are fortified with nourishing additives, perfumes, and dyes.

Naming

The term ''hard soap'' originates from the soap production process. During this process, the addition of salt (

sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

) to boiling soap mixed with a substantial amount of water causes the ''soap nucleus'' to separate and solidify, making it "harder" and allowing it to float on the surface.

Production

Through the process of

saponification Saponification is a process of cleaving esters into carboxylate salts and Alcohol (chemistry), alcohols by the action of aqueous alkali. Typically aqueous sodium hydroxide solutions are used. It is an important type of alkaline hydrolysis. When the ...

, fats (like tallow, pig, and bone fats) or

vegetable oils Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of edible plants. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed ...

react with

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

to form the sodium salts of fatty acids and glycerin.''Brockhaus ABC Chemistry'', VEB F. A. Brockhaus Publishing House Leipzig 1965, p. 2092. The resulting mixture is known as soft soap, which serves as a precursor for hard soap production. After adding sodium chloride (a process known as salting out), the soap nucleus rises and separates. The water-soluble glycerin and unwanted fat residues remain in the solution (see also

Properties and uses

The fatty acid salts formed during production constitute the actual soap and are effective cleaners due to their

surfactant Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent", coined in ...

properties. Using soap helps dissolve many water-insoluble substances, like fats and oils, making them washable with water. In most cases, hard soaps or products based on them are used for handwashing because they exhibit an

alkaline In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...

( pH value above 7) nature and can irritate the skin when in contact with mucous membranes. Hard soap has antiseptic qualities and can be used alongside warm water as a household remedy for paronychia. It's also used to shape dreadlocks. In the realm of detergents, soaps are generally secondary due to the creation of soap scum. They are primarily utilized as defoamers. Beyond cleaning, soaps also treat wood surfaces. They enhance the appearance of conifer woods, seal the wood's pores, minimize dirt accumulation, and prevent staining from fats or embedded

dyes Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy (DyE song), Fantasy" from his first album ''Taki 183 (album), Taki 183''. This video became popular, attracting ...

.Every Drop Preserves the Wood
published on June 18, 2020 / Issue 25/2020. In: Schreinerzeitung.ch For cleaning brushes, especially in

oil painting Oil painting is a painting method involving the procedure of painting with pigments combined with a drying oil as the Binder (material), binder. It has been the most common technique for artistic painting on canvas, wood panel, or oil on coppe ...

, hard soap ensures extended durability of the bristles or hairs. On occasion, water-based soap solutions are employed for

pest control Pest control is the regulation or management of a species defined as a pest (organism), pest; such as any animal, plant or fungus that impacts adversely on human activities or environment. The human response depends on the importance of the da ...

on cultivated plants, like against

thrips Thrips (Order (biology) , order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Entomologists have species description , described approximately 7,700 species. They fly on ...

and

aphids Aphids are small sap-sucking insects in the Taxonomic rank, family Aphididae. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white Eriosomatinae, woolly ...

References

External links

{{Wiktionary Soaps Surfactants

Naming

Production

Properties and uses

See also

References

External links