What is the Difference between Soap and Detergent?

Castellet Soap – Image: Stock Photo Exchange

A difference between soap and detergent? Though both clean what they are designed to clean, they possess a different chemistry and functionality.

Soap is defined as a metallic salt of a fatty acid—the metal often being an alkali metal such sodium or potassium, or an alkaline earth metal, such as calcium or magnesium. A fatty acid is often of plant or animal origin, and contains an aliphatic or straight chain carbon skeleton, with a carboxylic acid group at its end.

Detergents, on the other hand, are generally of synthetic origin. They’re generally not made insoluble by mineralized—so-called hard—water. Instead of a carboxylic acid group, the detergent may contain a sulfate or sulfonate group. In addition, detergents can contain an aromatic ring or rings. Detergents possess additional properties—and may serve as surfactants and foaming agents.

An example of a soap is sodium palmitate: CH₃(CH₂)₁₄-COO⁻ Na⁺

An example of a detergent is sodium lauryl sulfate: CH₃(CH₂)₁₂-OS(O)₂-O⁻ Na⁺


3 Responses to What is the Difference between Soap and Detergent?

  1. I’m a soap maker. Excellent article.

  2. Barbara says:

    I did not know these facts. Quite fascinating.

  3. MegL says:

    In the UK, most shampoos and shower gels are detergents, as is what we term “washing up liquid”, which I think Americans call “dish soap”. Mt granddaughters love bubble bath (detergent) but it is so hard to get the bubbles to drain after the bath but I have found that washing your hands with a piece of soap in the detergent water helps get rid of the bubbles. They seem to work against each other!

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