why does adding a salt solution cause soap to precipitate

I am struggling with fully answering two questions that are fairly similar. 1. Why should the potassium salts of fatty acids yield soft soaps? - I know that sodium yields what is considered as hard soap and potassium yields soft soaps. I also know that potassium is more soluble in water than sodium, but is this in fact that entire answer? 2. Why is soap derived from coconut oil so soft? Again I realize that water solubility is high here but I'm just not confident in understanding why. 3.


Why does adding a salt solution cause soap to precipitate? Here is my answer for this:
It is a general rule that a fatty acid salt (soap) becomes less soluble as a salt is added to solution. The soap will precipitate because the decrease in solubility. The loss in solubility is because the positively charged ion from the salt will attach or attract to the negative head group of the salt and will precipitate out of solution.


Under normal conditions, the negatively charged head group would be attracted to the polar water molecule and dissolve in water, but this cant happen if the positive ion (say Ca2+) has already attached. Thanks everybody I'm SO glad I found this place. Our school has no tutors and our teachers are rarely available. THANKS! No, when salt is added to water it both raises the boiling point and lowers the freezing point.


Because salts break up in water, the pieces will stop water from freezing. In order to freeze, a water molecule must form more attractive forces with the molecules around it than it forms in the liquid state. The ions of a salt will get between the water molecules stop them from forming attractive forces, raising the freezing point. Salt will lower the boiling point because the ions on the surface of the water will take the place of water molecules on the surface.


Since boiling happens on the surface, the fewer water molecules on the surface the higher the boiling point. The more ions the salt breaks into, the more effective this is. For example, table salt is NaCl and becomes Na+ and Cl- while road salt is CaCl2 and will break up into three ions, Ca+ and 2Cl-.

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