The fatty acid portion is turned into a salt because of the presence of a basic solution of the NaOH. A drop or two of soap in water forms a monolayer on the water surface as shown in the graphics on ...The fatty acid portion is turned into a salt because of the presence of a basic solution of the NaOH. A drop or two of soap in water forms a monolayer on the water surface as shown in the graphics on the left. That leaves the polar carboxylate ion of the soap molecules are sticking out of the oil droplets, the surface of each oil droplet is negatively charged. The graphic on the left although not strictly a representation of the above description is a micelle that works in much the same fashion.
