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Organic Chemistry
Soaps and Detergents

What is the difference between hard soap and soft soap?


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April 20, 2012 8:51AM

Soap is partially comprised of fatty acids; long molecules derived from plant or animal fat.

The liquid soaps use shorter, fats, which tend to be more liquid than solid (compare

olive oil, for example, to palm oil).

The above does not answer the question... The answer is that soft soaps tend to dissolve more readily into water, due to the ions of the soap being able to stabilise and disperse into the water. Hard soaps tends to have ions that make dissolution into water difficult. In other terms, soft soap dissolves easily, where as hard soaps do not.

To add to this - soaps made with KOH (caustic potash) give more soluble soap molecules than those made of NaOH. Therefore KOH soaps are soft and are used for liquid soap production and NaOH soaps are hard.