Soap In simple terms, is when you combine an oil or fat (which is acid) with Sodium Hydroxide (Caustic Soda or Lye, which is an alkali) to form soap, which is a salt. The chemical reaction between acid and alkali to form salt is called saponification.
This happens because the base is made up of one hydroxide ion. For the most part, people use Sodium Hydroxide (one sodium ion and one hydroxide ion) as their base. The sodium doesn’t have any effect in the saponification process, so a number of alternatives could be used as a base such as Potassium Hydroxide; however this is more commonly used for liquid soaps. Many acids can be used to saponify, olive oil, palm oil and coconut oil to name a few. Each oil has its own unique triglycerides (which are compounds made of three fatty acids attached to one glycerine molecule) which react with Sodium Hydroxide base differently, and the amount of base required varies greatly on the oil being used.
When you react oils with sodoium hydroxide, what happens during the reaction is the triglycerides within the oil is releasing their single glycerol molecule (creating skin nourishing glycerin) allowing the fatty acids to combine with the hydroxide ions, forming soap.
Therefore, two reactions are taking place, the first is the glycerol from the oil turning into beneficial glycerine, and the second is the acid and the alkali combining to form soap. Simple!