Fats and Oils – SS3 Chemistry Lesson Note (First Term)

Fats and oils are lipids. They are esters of propane-1,2,3-triol, each molecule of which is esterified with three fatty acid molecules. Fats are usually solids of animal origin, while oils are liquids mainly from plants. Both are insoluble in water and soluble in organic solvents such as ether and chloroform.

Behavioural objectives

By the end of the lesson, students should be able to:

1. identify the sources of fats and oils
2. identify the properties of fats and oils

Instructional techniques

• Identification
• Explanation
• Questions and answers
• Demonstration
• Videos from source

Instructional materials

• Videos
• Loudspeaker
• Textbook
• Pictures

What are fats and oils?

Fats and oils belong to a general group of compounds known as lipids. Fats are solids usually of animal origin, while oils are liquids mainly from plants. Both are esters of the trihydric alkanol, propane-1,2,3-triol. Each molecule of propane-1,2,3-triol is esterified with three molecules of fatty acids.

What are the sources of fats and oils?

• Fats and oils are found in both plant and animal sources.
• Plant sources include seeds, nuts, olives and avocados.
• Animal sources include meat, fish and dairy products.

What are the physical properties of fats and oils?

1. State at room temperature

• Fats are typically solid at room temperature.
• Oils are liquid at room temperature.

2. Melting point

• Fats have a higher melting point, so they are solid at room temperature.
• Oils have a lower melting point, so they remain liquid at room temperature.

3. Solubility

• Fats and oils are insoluble in water.
• They are soluble in organic solvents like ether and chloroform.

4. Density

• Fats are denser than oils due to their solid nature.
• Oils have a lower density because they are in a liquid state.

5. Odour and flavour

• Both fats and oils may carry specific odours and flavours based on their source and processing methods.

6. Colour

• The colour of fats and oils can vary, ranging from clear to yellow or brown, depending on factors such as impurities, processing and source.

What are the chemical properties of fats and oils?

1. Hydrolysis

Fats and oils can undergo hydrolysis, a chemical reaction where they react with water in the presence of an acid or base to break down into glycerol and fatty acids.

Triglyceride + 3H₂O → Glycerol + 3 Fatty acids

2. Saponification

Saponification is a reaction with a strong base (such as sodium hydroxide or potassium hydroxide) to produce soap and glycerol.

Triglyceride + 3NaOH → Glycerol + 3 Soap molecules

3. Polymerisation

Under certain conditions, fatty acids in fats and oils can undergo polymerisation, forming polymers. This process is often undesirable, as it can affect the quality of the fat or oil.

4. Isomerisation

Isomerisation reactions can occur in unsaturated fatty acids, leading to the conversion of cis-isomers to trans-isomers. Trans fats are associated with health concerns.

Evaluation

1. Mention three sources of fats and oils.
2. What is saponification? Describe how saponification takes place.
3. Identify four uses of fats and oils.

Assignment

1. State three physical properties of fats and oils.
2. Write the word equation for the hydrolysis of a triglyceride.

Closing the lesson

The teacher commends the students positively.