Question

For a chemistry lab about a saponification reaction, why would you test your soap using CLR in the hard water reactions, shaking until you see a change?

This is from the hard-water reaction section of the lab.

Each test tube had dissolved natural soap in water. CLR was added to tube #1 with 5% CaCl2 added prior, tube #2 with 5% MgCl2 added prior, and into tube #3 with tap water added prior.

Tube #1 turned white and layered

Tube #2 turned white

Tube #3 turned white and layered

What does this tell us and why?

(does it have something to do with the fact that the natural soap made does not work in hard water or in acidic water?)

Answer 1

As we know that the natural soaps are generally the sodium salt of long-chain fatty acid which removes the dust particle via micelles formations.

In hard water, there are high contents of minerals such as Ca2+ and Mg2+, and these divalent cation binds to the soap and form the white, insoluble solid. That's why you are observing the white layer or white color solution.

Here the simple reaction has given which happen with soap in hard water-  

RCOO Na Hard Water Containg Ca2+ and Mg2+ (RCOO)2M White Ppt Soap RCOO = any long chain alkyl acid group such stearate (C17H35COO-)

Here M = Ca2+ or Mg2+