5.1.1 - Laboratory Activity : Preparation of Soap by Saponification

Laboratory Activity 5.1.1: Preparation of Soap by Saponification

Aim: To prepare soap through the saponification process.
Problem statement: How is soap prepared in the laboratory?
Hypothesis: The vegetable oil will react with the alkali to form soap during saponification process.
Variable:

	»	Fixed variable : Quantity of sodium hydroxide and vegetable oil
	»	Manipulated variable : Type of vegetable oil
	»	Responding variable : Types of ions discharged at the anode and the cathode

Material: » Sodium hydroxide 5mol dm-3 » Sodium Chloride » Corn oil » Soy oil » Palm oil » Olive oil

Apparatus: » Beaker » Glass rod » Measuring cylinder » Tripod stand » Wire gauze » Spatula » Bunsen burner

Procedure:

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1. The animation below shows the arrangement of the apparatus and the observation of the experiment. 2. 5cm3 of palm oil are measured by measuring cylinder and poured into a beaker. 3. 30cm3 of sodium hydroxide are measured and added into the beaker. 4. The mixture is stirred constantly and heated until boiling for about 10 minutes. 5. 50cm3 of water and one spatula of sodium chloride are added into the beaker. 6. The mixture is boiled for another 5 minutes and then cool down to room temperature. 7. Product formed are filtered and dried with pieces of filter paper. 8. The residue is then touched using fingers. 9. The residue is then mixed and stirred together with water 10. The experiment is repeated with different vegetable oil.

Observation:

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Dilute sulphuric acid Vegetable oil Product formed Smoothness Test with water Palm oil White semi solid Smooth Many bubbles are produced Corn oil White semi solid Smooth Many bubbles are produced Soy oil White semi solid Smooth Many bubbles are produced Olive oil White semi solid Smooth Many bubbles are produced

Analysis:

	►	The white semi-solid is called soap as it will form bubbles with with water.
	►	The chemical equations for the formation of soap are shown below: ○ Palm oil + alkali → sodium salt of fatty acid + glycerol ○ Corn oil + alkali → sodium salt of fatty acid + glycerol ○ Soy oil + alkali → sodium salt of fatty acid + glycerol ○ Olive oil + alkali → sodium salt of fatty acid + glycerol

Discussion:

	►	The presence of sodium chloride helps the soap to precipitate. Sodium chloride makes the soap less soluble by helping the solid soap to form from the liquid soap solution.
	►	The flame should be controlled during the boiling process to avoid bubbling of mixture.

Conclusion:

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The boiling of different vegetables oil with concentrated alkaline solution will procedure soap.

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