How is soap made?

Introduction

     "Contrary to what you might think, soap was not invented for purposes of personal hygeine. Rather, it was invented early on to solve a problem with textiles: wool as it comes from the sheep is coated with a layer of grease that interferes with the application of dyes. And colorful yarns were valued very early in the history of textiles. A colored garment was an expensive garment and therefore an indication of wealth and status.

     Soap very likely counts potash as a direct ancestor. If you rub a solution of potash or soda ash between your fingers, it feels soapy. If you taste it, it tastes soapy. In fact, another name for soda ash is washing soda and you can buy it in the grocery
store in the laundry detergent section.

     Potash by itself is not a very effective soap. If fat is boiled in potash, however, it makes a pretty good soap. And a really strong soap comes from boiling fat in a strongly basic solution, such as a lye solution." (From Caveman Chemistry)

From the Caveman site on soap and our discussions you should recall the following ideas"

• Compounds can be classified as ionic, polar and non-polar
• Water is a polar compound that dissolves polar and ionic (charged) molecules
• Fatty acids are have a polar head and a non-polar tail
• Three fatty acids combined with a glycerol (alcohol) to form a non-polar triglyceride
• Fats are also called lipids
• Lard is a saturated fat and solid at room temperature
• Polymers are decomposed by hydrolysis
• Acids have low pH, bases have high a pH

To make soap we have to break the triglyceride into its fatty acid and glycerol components. By using a strong base, such as lye, the lipid is hydrolyzed, the free fatty acids (FFA) will be solution as large cations (+ ions). This process is called saponification.

When soap meets grease, the non-polar FFA tail dissolves in the non-polar grease, while the polar FFA head dissolves in water. In this matter, grease particles become surrounding by water as an emulsion and can be rinsed out. This is what happens when you wash. It is also very similar to what happens when you blow soap bubbles.

When working with lye DON"T breath fumes. If you do, you will notice a strange taste in your mouth. The lye is reacting with the lipids forming cell membranes on your tongue, and your tongue surface is turning into soap. Yuck!! In the same manner, your skin will feel slimy if you get lye on it!!

Safety

Always wear rubber glove and safety glasses when handling lye. Wash off immediately if you get careless. If you get lye in your eyes, you should wash them immediately with cold water and call a hospital. If you are careless enough to ingest (eat) lye, go straight to an emergency room!!

Procedure

We will use glassware. Lye in an aluminum container will react violently !!!

Bring to the lab on soap day: A clean two-liter bottle. I have molds for you to use.

I will have ready for you enough materials for each two-person team to have the following:

• 125 ml of melted lard
• 125 of lye solution (19.2 gr in 125 ml H₂O)

1. Bring your 2-liter bottle to me and I will pour in 125 ml of lye. Then, you will add 125 ml of lard.
2. The lye and lard will separate into two layers like salad dressing.
3. Put the cap on the bottle and gently shake the contents.
4. Stop shaking and see if the layers still separate. If they do, then continue shaking gently.

 

 

Note: When the mixture is ready it will coat the inside of the bottle likebutter milk as it runs down to the bottom of the bottle when you stop shaking)

5. When the layers no longer separate, pour the contents into your mold.
6. Throw your 2-liter bottle in the recycle bin. Clean up your mess.
7. Wait two weeks for the soap to cure
8. Check the pH of your soap to see if it is now neutral? (If not, it might burn)

Quiz
    What is lye?
    What is saponification?
    What is a base?
    What is the difference in potash and lye?
 

Project
   I will shave off some of your soap and mix it with water. If it makes suds you pass!