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Mark Lambert

If a tenside is a base and in a watery solution, does adding acid have any changing effect on its decreased surface tension?

Ahmed Jawad  Follow

The answer depends on the kind of base. Surfactants which are more strongly basic can exist partially as non-ionized, neutral molecules at lower pHs. The neutral molecule is usually a weaker surfactant than its ionized counterpart. So adding a strong acid to such an aqueous surfactant would raise the surface tension. An example is sodium dodecylcarboxylate in water. Carboxylic acids are only partially ionized, especially at acidic pHs.

Surfactants which are weakly basic tend to stay ionized even at acidic pHs, so their surface tension lowering effect is less influenced by the addition of a strong acid. An example is sodium dodecyl sulfate in water.

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