Saponification

Saponification

Aim / Objective:

To produce soap using a base-catalyzed saponification of triglycerides.

Introduction:

Soap molecules are the conjugate bases of fatty acids.  Vegetable oils and animal fats are the main materials that are “saponified”. These fats are in fact tri-esters of a glycerol molecule. In the traditional one-step process, the triglyceride is treated with a strong base (e.g., lye), which accelerates cleavage of the ester bond and releases the fatty acid in its conjugate base form, and glycerol.

 

A General Reaction is as follows:

Saponification using trigylcerides

Saponification using triglycerides

Different alkyl (R) groups are found in different fats and oils.  Depending on which triglyceride (tri-ester) you choose, your soap will have different properties.  For example, some oils make soft or liquid soaps, and some fats make hard soap.

Materials/Apparatus:

Tripod stand, wire gauze, spatula, breaker, 2 measuring cylinder, glass stirring rod, filter funnel, filter paper, Bunsen burner, 2 test tubes with bungs, test tube rack, evaporating dish, castor oil, concentrated sodium hydroxide (NaOH), distilled water, perfume, dye, saturated solution of sodium Chloride (NaCl)

Method / Procedure:

  1. Half fill a beaker with tap water and set to boil.
  2. Place 2cm3 castor oil into evaporating dish. Use a measuring cylinder to pour 10cm3 of concentrated NaOH into the castor oil
  3. Place the evaporating dish atop the beaker of boiling water
  4. Stir the mixture of oil and alkali with a glass stirring rod for 10-15 minutes
  5. Add 10cm3 of the saturated salt solution to the basin and stir the mixture
  6. Turn the Bunsen burner off and leave to cool for 2-3 hours
  7. Use a spatula to scrape the crust of soap which is formed on the side of the evaporating dish
  8. Put this material in a beaker
  9. Add water to the material in the beaker and heat the beaker.
  10. Add a few drops of dye and perfume to the beaker

Discussion:

1. What is the name given to this process?

>>> Saponification

2. Write the word equation for this reaction

>>> Fat/Oil + NaOH        =         Glycerol + Soap (Sodium Salt of Acid)

3. Why is the product of saponification called a salt?

>>> This experiment is the hydrolysis of a fatty acid, usually from lye and fats. The process produces a carboxylate which is a sodium salt.

4. Why was ethanol added to the mixture of fat and base?

>>> Ethanol (ethyl alcohol) is added to the mixture to make the soap transparent. Transparent soap is also known as glycerin.

5. How does soap emulsify fats and oils?

>>> Grease and oil are nonpolar and insoluble in water. When soap is mixed with oils and fats  the nonpolar hydrocarbon portion of the micelles of the soap break up the nonpolar oil molecules. A different type of micelle then forms, with nonpolar oils and fats molecules in the center. Therefore, grease and oil and the ‘dirt’ attached to them are caught inside the micelle and can be rinsed away.

6. Explain the difference in “hard water” and “soft water”

Hard water is any water containing a great quantity of dissolved minerals while soft water is treated water in which the only cation (positively charged ion) is sodium.

7.  Explain which water is better to use with soap

>>>Soap is less effective in hard water as it will react with the ions in the water to form the calcium or magnesium salt of the organic acid of the soap. These salts are insoluble and form grayish soap scum, but no cleansing lather.

 

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