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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: kenny1999 on April 25, 2011, 08:39:08 AM

Title: soapy detergent or soapless detergent?
Post by: kenny1999 on April 25, 2011, 08:39:08 AM

what is the difference between the structure of soapy detergent and saopless detergent to classify them ? is it a must for soapy detergent to contain COO-
as the hydrophilic end while SO3- (sulphonate) or SO4- (sulphate group)??

By the way, if we want to treat the oil spill on the sea, should we use soapy or soapless detergent given that only one of these two could be picked. and why?

Thanks!

More questions to ask

- why straight chained detergent is biodegradable while non-biodegradable for the branched chained one?

ThanKs1

Title: Re: soapy detergent or soapless detergent?
Post by: softmatterresources on April 26, 2011, 02:43:50 PM

Hi,

I have never heard of the expression "soapy detergent" before. If soapy detergent means that it contains soap then it can't be a detergent. Soaps and detergents contain different chemicals and detergents are "non-soapy" by definition.

Soaps are surfactants made by the soaponification of fats and detergents are surfactants made from hydrocarbons obtained from crude oil.

A soap will always have the COO- group in it as they are formed by the base hydrolysis of the ester bonds in fats (which will always form the COO- group and an alcohol. Soaps also tend to have longer hydrgocarbon chains than detergents (C18 compared to a general ~C12 for detergents )

The surfactants in detergents can have many different head groups. Many have the sulphonate and sulphate groups like you said, but they can also have phosphate or carboxylate groups. Then there are the cationic head groups such as amine groups (see CTAB). There are also polar head groups such as PEG.

In terms of which are used on oil spills...I’m not sure. Detergents are more likely to be toxic to fish (especially phosphate containing ones which are well known to be bad for wildlife).