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In most articles and texts that I've read, soaps and detergents seem to be talked about collectively. I know that they are both surfactants and that soaps are usually natural, in comparison to detergent which is artificial. However, what are the differences in terms of chemical structure and properties (between soap and detergent)?

NOTE: not the same as Is there an important difference between soap and detergent?, as I'm asking about chemical structure and properties rather than the effects in everyday life.

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There is no restriction that soap be natural or unnatural. Soap are salts and detergents are not necessarily salts. The latter is a very broad term. Soap has a narrow meaning.

IUPAC clearly defines soap as

"A salt of a fatty acid, saturated or unsaturated, containing at least eight carbon atoms or a mixture of such salts."

Just note that not all soaps are used for cleaning nor there is any condition that they should be soluble in water. Insoluble soaps of metallic salts serve as lubricants.

Similarly,

IUPAC defines a detergent as

"A surfactant (or a mixture containing one or more surfactants) having cleaning properties in dilute solutions (soaps are surfactants and detergents)"

Just like banana is a fruit but not all fruits are bananas, in the same way, all water soluble soaps are detergents and surfactants. Not all detergents are soaps.

Visit the IUPAC Gold Book and search the entries detergents and soap.

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  • $\begingroup$ Anything chemical structure wise? Like are there differences in the chemical structure of the molecules $\endgroup$ – An0n1m1ty Jun 20 '20 at 5:36
  • $\begingroup$ @M.Farooq I suppose you are trying to quote IUPAC's web version of "Gold Book". Keep in mind you can include an URL in a format [<text>](<link>), and use > for quoting third-party sources. Currently the quoted definitions are not referenced. $\endgroup$ – andselisk Jun 20 '20 at 8:49
  • $\begingroup$ @andselisk, You might have noticed that I do not provide links to papers but write the textual form form of the reference. The intention is to promote students to search themselves. In my humble opinion, they should be curious enough to search the quote and land at the right website within a few seconds. You are right, I should provide the main page link to IUPAC Gold book so that they at least scroll down and look up the relevant entry. $\endgroup$ – M. Farooq Jun 20 '20 at 12:45
  • $\begingroup$ @An0n1m1ty, I have given you enough description to begin the journey of search. Now it is your duty as future curious scientist to search the web. Search what how do fatty acids salts look like. Also read the Wikipedia entry on detergents and start from there. $\endgroup$ – M. Farooq Jun 20 '20 at 12:48
  • $\begingroup$ @M.Farooq While I can clearly see you mean well, the problem is that SE sites are not exactly educational in a sense there is little to no dialogue in Q&A section, and, as a consequence, all answers must be complete and self-contained. Hints, unfinished posts and general recommendations are not answers. Yours, however, is, but it lacks referencing, which if good in a pedagogical sense for one person (OP), but drastically lowers the quality of your answer for all other users. $\endgroup$ – andselisk Jun 20 '20 at 14:04
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The main difference between soap and detergent is the effects they produce when dissolved into pure water or tap water. Usually, tap water contains calcium carbonate, or at least calcium ions. When dissolved into tap water, soap reacts with these calcium ions, producing an insoluble substance which could be called "calcium soap". This substance stays usually in emulsion in water, making it cloudy or turbid. In the rotating washing machines, this deposit remains in the clothes, which become rough when dry. This does not happen with detergents, which do not react with calcium ions, and wash without producing this turbidity.

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