Soap scum or lime soap is the white solid composed of
calcium stearate
Calcium stearate is a carboxylate salt of calcium, classified as a calcium soap. The salt is a component of some lubricants, surfactants, as well as many foodstuffs. It is a white waxy powder.
Production and occurrence
Calcium stearate is produc ...
,
magnesium stearate
Magnesium stearate is the chemical compound with the formula . It is a soap, consisting of salt containing two equivalents of stearate (the anion of stearic acid) and one magnesium cation (Mg2+). Magnesium stearate is a white, water-insoluble pow ...
, and similar
alkaline earth metal
The alkaline earth metals are six chemical elements in group (periodic table), group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar p ...
derivatives of fatty acids. These materials result from the addition of
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 ...
and other
anionic 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 ...
s to
hard water
Hard water is water that has a high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bic ...
. Hard water contains
calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
and
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
ions, which react with the surfactant anion to give these
metallic or lime soaps.
:2 C
17H
35COO
−Na
+ + Ca
2+ → (C
17H
35COO)
2Ca + 2 Na
+
In this reaction, the
sodium
Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...
cation in soap is replaced by calcium to form
calcium stearate
Calcium stearate is a carboxylate salt of calcium, classified as a calcium soap. The salt is a component of some lubricants, surfactants, as well as many foodstuffs. It is a white waxy powder.
Production and occurrence
Calcium stearate is produc ...
.
Lime soaps build deposits on fibres, washing machines, and sinks. Synthetic
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 ...
s are less susceptible to the effects of hard water. Most
detergent
A detergent is a surfactant or a mixture of surfactants with Cleanliness, cleansing properties when in Concentration, dilute Solution (chemistry), solutions. There are a large variety of detergents. A common family is the alkylbenzene sulfonate ...
s contain
builders
Builder may refer to:
Construction
* Construction worker, who specializes in building work
* Carpenter, a skilled craftsman who works with wood
* General contractor, that specializes in building work
** Subcontractor
* Real estate developer, who ...
that prevent the formation of lime soaps.
See also
*
Water softening
Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extend ...
*
Tadelakt
''Tadelakt'' () is a waterproof plaster surface used in Moroccan architecture to make baths, sinks, water vessels, interior and exterior walls, ceilings, roofs, and floors. It is made from lime plaster, which is rammed, polished, and treated with ...
, a form of lime-soap-based waterproof plaster
*
Qadad
''Qadad'' ( ''qaḍāḍ'') or ''qudad'' is a waterproof plaster surface, made of a lime plaster treated with slaked lime and oils and fats. The technique is over a thousand years old, with the remains of this early plaster still seen on the ...
, another form of lime-soap waterproof plaster
References
{{Reflist
Water treatment
Soaps
Calcium compounds
Magnesium compounds