Science Buddies: "Ask an Expert"

We made soap in the lab and chose to test how the temperature and type of base used will effect the pH and solubility of our soap. We were asked why we chose temperature and base as our independent variables but I cannot think of chemical ways as to why we chose those. Is it accurate to say we chose temperature because we figured a higher temperature would mix our solutions better and produced a more solidified soap? Also, would a good rationale for the base be because we though a more basic base would produce a more basic soap? I am just not sure if these answers need to be on a more chemical level or if they could be broad like this.

My next issue is with the explanations of the dependent variables. Our solubility test consisted of measuring the amount of bubbles produced when our soap was mixed with water but, again, I do not know how that chemically explain how the production of bubbles would measure the solubility of the soap.

Hi jennchambers,

Making soap involves reacting a fat or oil with a strong base. Higher temperatures usually increase how fast reactions take place. And most chemicals are more soluble at higher temperatures. So you might expect more a more complete soap making reaction at a higher temperature.

The base used in soap making needs to be strong, or one that is completely dissociated in water. Usually either sodium hydroxide or potassium hydroxide is used. And the finished soap will be either sodium or potassium salts of a mixture of fatty acids. You might expect some effect on pH or solubility due to a difference in the cation.

A bit of online searching will turn up quite a few references about the chemistry of soap making and how soap works. A few examples are listed below.

http://www.labmuffin.com/make-your-own- ... ap-making/

http://amrita.olabs.edu.in/?sub=73&brch=3&sim=119&cnt=1

http://chemistry.elmhurst.edu/vchembook/554soap.html

I hope this helps. Please post again if you have more questions.

A. Norman