formation of scum

Question

write an equation to show the formation of scum when a soap is used in water containing calcium hydrogentrioxocarbonate (IV)

Answer 1

calcium hydrogentrioxocarbonate (IV) is essentially calcium bicarbonate, Ca(HCO3)2, which isn't really part of everyday water.  CaCO3 is found everyday in hard water. but the reaction with soap will not be different between the two, as an insoluble Ca salt of the fatty acid found in soap will form (scum).

Let the fatty acid in soap be represented by C17H35COO-Na+ which in water => C17H35COO^-

Then reaction with Ca(HCO3)2, which dissociates to Ca^2+ + 2 HCO3^-

2C17H35COO^- + Ca^2+ ===> (C17H35COO)2Ca which is insoluble and referred to as scum.