Abstract:
Soap scum is generated from long chain fatty acids of soap reacting with divalent cation, especially calcium and magnesium ion in natural hard water. It is precipitate on the surface of sink and bathtubs as a white stain. Soap scum can be removed by using an appropriate surfactant and a chelating agent. The purpose of this research was to investigate the equilibrium solubility of different soap scums from steric acid (S) or Lux commercial soap (CS) and water containing with pure Ca, pure Mg, mixed Ca and Mg at a molar ratio of Ca: Mg = 4:1 or natural hard water (NHW) with a high hardness in different solution systems: pure water pH 4, dimethyldodecylamine oxide/tetra sodium glutamate diacetate (DDAO/Na4GLDA), and dimethyldodecylamine oxide/disodium ethylene diamine tetra acetate (DDAO/ Na2EDTA) pH 11 were investigated at a constant temperature of 25 ℃. The results showed that soap scums synthesized from stearic acid in the Na2EDTA/DDAO and Na4GLDA/DDAO system seem to have lower equilibrium solubility than commercial soap scums. In addition, calcium commercial soap scum was higher equilibrium solubility than the magnesium commercial soap scum. The further study of dissolution rate showed that for both stearic acid and commercial soap in natural hard water is no significant different in the Na2EDTA/DDAO and Na4GLDA/DDAO system.
