Soap scum
White solid resulting from addition of soap to hard water
title: "Soap scum" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["water-treatment", "soaps", "calcium-compounds", "magnesium-compounds"] description: "White solid resulting from addition of soap to hard water" topic_path: "general/water-treatment" source: "https://en.wikipedia.org/wiki/Soap_scum" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0
::summary White solid resulting from addition of soap to hard water ::
Soap scum or lime soap is the white solid composed of calcium stearate, magnesium stearate, and similar alkaline earth metal derivatives of fatty acids. These materials result from the addition of soap and other anionic surfactants to hard water. Hard water contains calcium and magnesium ions, which react with the surfactant anion to give these metallic or lime soaps. : In this reaction, the sodium cation in soap is replaced by calcium to form calcium stearate.
Lime soaps build deposits on fibres, washing machines, and sinks. Synthetic surfactants are less susceptible to the effects of hard water. Most detergents contain builders that prevent the formation of lime soaps.
References
References
- Angelo Nora, Alfred Szczepanek, Gunther Koenen. (2005). "Metallic Soaps".
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