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Saponification

Saponification can be defined as a “hydration reaction where free hydroxide breaks the ester bonds between the fatty acids and glycerol of a triglyceride, resulting in free fatty acids and glycerol,” which are each soluble in aqueous solutions.

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 Reaction

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 2cmcastor 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.

Separating a mixture of oil and water using a separating funnel

Aim / Objective:

To separate a mixture of cooking oil and water.

Abstract:

In this experiment, an immiscible mixture of oil and water was separated using a separating funnel.

Materials/ Apparatus:

measuring cylinder, retort stand, beaker, clamp, separating funnel, conical flask, cooking oil and water,

Method / Procedure:

  1. Use a measuring cylinder to measure 10cm3 of cooking oil and pour it into the conical flask.
  2. Use another measuring cylinder to measure 10cm3 of water and add to the conical flask with the oil.
  3. Mix both liquids by shaking the flask vigorously.
  4. Use a clamp to attach the separating funnel to a retort stand. Ensure that the separating funnel is in the closed position and pour in the mixture of oil and water.
  5. Allow the mixture to settle for a few minutes. Place a beaker under the mouth of the separating funnel and allow the mixture of water to run off in the beaker slowly.
  6. Collect the remaining portions of water and oil and then the pure oil.

Diagram of apparatus showing the separation of a mixture of oil and water using a separating funnel

Suggested Results:

When the water was added to the cooking oil, it was seen to be the more dense liquid hence the water settled on top of it. Also in between the layer of pure oil and the layer of pure water, there was a layer consisting of a mixture of oil.

Diagram of apparatus showing the separation of a mixture of oil and water using a separating funnel

Discussion:

1.What type of mixture is the separating funnel generally used to separate?

>>>The separating funnel is generally used to separate a mixture of immiscible liquids. Immiscible meaning that the liquids do not mix but separate into distinct layers

2. Explain why this technique was suitable in separating the oil from the water.

>>>This technique was ideal for the experiment for when water is mixed with oil, it is known to be immiscible. It forms a total of three layers, a layer of pure oil, pure water and a layer of both water and oil mixed together.

3. Explain the chemical principle underlying the type of mixture formed by oil and water

>>>Pure oil doesn’t mix with water because water is polar solvent and oil is non-polar and like dissolves like. But in between the layer of pure oil and pure water there was a layer of both oil and water. This type of technique can be said to be an emulsion.

4.To what position should the top of the funnel be turned when opening it?

>>>The top should be vertical to allow the water to run out and must be closed before the oil reaches the bottom of the funnel

5.Can separating funnel be used to separate a mixture of ethanol and water? Explain your answer

>>>No. A separating funnel cannot be used to separate ethanol and water because ethanol will dissolve in the water due to polarity hence being classified as miscible liquids. So in order to separate a mixture of ethanol and water, one would have to use fractional distillation.

Source of Error/ Limitations/ Assumptions: 

–  Improper technique of decanting, thus allowing for the layers that were collected to be not entirely pure.

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