Group Members:
Caitlin Harrington - Tyler
Ranti Ositelu - Narrator

Movie vs. Reality: Soap Making

Making Soap from Ranti Ositelu on Vimeo.

Water, the substance usually attributed to cleaning surfaces has a very high surface tension which makes it bead up on surfaces, which slows wetting of the surface and inhibits the cleaning process. Soaps reduce surface tension and allow for water to wet surfaces quicker. Surfactants perform other important functions in cleaning, such as loosening, dispersing in water and holding soil in suspension until it can be rinsed away.

Soaps are made from fats and oils by treating them with a chemically strong alkali (sodium or potassium hydroxide). As you saw in our video, we used rendered fat and sodium hydroxide to make our soap.
Fats are made up of triglyceride molecules, which are composed of three fatty acids and a molecule of glycerin. Fatty acids are the components of triglycerides that are used in soap making. They are weak acids that are composed of a carboxylic group consisting of one hydrogen atom, two oxygen atoms, and one carbon atom attached to a carboxylic acid group. The general structure is shown below.
Alkalis are soluble salts of alkali metals like sodium or potassium. Originally the alkali used in soap making was gathered from the ash of a fire, but today it is commercially made. Usually it can be found in the supermarket under the name of lye. The reaction of the triglyceride and alkali is called saponification and is the most widely used soap making process. Required steps of this method are heating the oil and letting it react with a liquid alkali at the same temperature. When potassium hydroxide is used as the alkali the soap is softer and liquid and is found in liquid hand soap and shaving cream. When sodium hydroxide is used as the alkali a bar of soap is produced. A picture of the saponification process is shown below:
The reaction of lye and water is highly exothermic. Lye is a corrosive alkaline substance, commonly sodium hydroxide. When lye was orignally used by ancient peoples to soap it was leached from hardwood ashes. Now, lye is commercially naufactured using a membrance cell method.
The carboxylic end of the soap molecule is attracted to water making it hydrophilic. The hydrocarbon chain is attracted to oil and grease, but it is repelled by water making it hydrophobic.


How Soap Works
Water is a polar molecule that has distinct positive and negative charges in the molecule. Chemicals such as table salt with happen to be made up of a collection of charged particles dissolve readily in water. However, oils, which are non polar and have no particular electrical charge do not dissolve in water because they prefer to bond with/dissolve in other non polar substances.
For example, when you have a really greasy pan and you pour water on it to get the grease off, you notice that you end up just sliding the grease around. The grease does not dissolve in the water because it is non polar. Soap acts as an agent that can interact with both the grease and the water. The hydrophobic carbon chain is attracted to the grease, and the hydrophilic carboxylic end is attracted to the water. As the soap is spread around the grease the hydrophobic end of the soap molecules holds on to it and eventually the grease leaves the pan. The soap also holds that grease suspended in solution so that it can be rinsed away.

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