Activity 3 1-13-11

Show a chemical structure for soap.

                                               or

What is unique about the polarity(charge characteristics) of soap?

 

It is the long hydrocarbon chains of the stearate anions that dissolve the oils and greases.  If water containing dissolved soap is mixed with oil, the hydrocarbon chains strongly attract the oil, while the ionic ends keep the soap dissolved into water.    The oil spot is broken up into small droplets and dispersed into the water.    The "tails" of many soap anions are needed to remove each oil droplet.
 
While the sodium salt of stearate ions and the anions of other soaps are soluble in water, the calcium and magnesium salts are not.  Hard water contains these metal cations, so the metal salts precipitate, reducing the oil-dissolving efficiency of the soap.  "Bathtub ring" originates from the precipitation of soap by hard water.  Thus, soaps do not clean well in hard water until most of the metal cations have been precipitated by reacting with the soap.  In recent years, this problem has been solved by replacing soaps with detergents, which are generally compounds with long hydrophobic tails and the charged sulfate group such as sodium dodecyl sulfate, Na[CH₃(CH₂)₁₁OSO₃].    The calcium and magnesium salts of detergents generally remain soluble in water.
http://www.brookscole.com/chemistry_d/templates/student_resources/0030012910_kotz/appchem/ch11/carbon10.html

How does soap work?

Soap is mainly considered a fat, so when rubbing the fat together on your hands it is rubbing the oils and dirt off of your hands.