Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Fats and Oil
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Fats and Oil
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Subject: Chemistry
Class: Senior Secondary 3
Term: 1st Term
Week: 5
Theme: Chemistry Of Life
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Identify sources of fats and oils differentiatebetween fats and oils State the physicaland chemicalproperties of fats and oils. Explainsaponification usingrelevant equations Test for fats State the uses of fats and oil
Fats and oils are obtained from both animal and plant sources.
Animal Sources (Predominantly Fats): These typically contain a higher proportion of saturated fatty acids, making them solid at room temperature.
Butter: From milk.
Lard: From pig fat.
Tallow: From beef or mutton fat.
Fish oil: From fatty fish like mackerel, salmon (note: fish oil is an oil despite being animal-derived, due to high unsaturation).
Cod liver oil: From cod liver, rich in vitamins A and
D. Vegetable Sources (Predominantly Oils): These typically contain a higher proportion of unsaturated fatty acids, making them liquid at room temperature.
Palm oil: Extracted from the fruit of the oil palm (very common in Nigeria).
Groundnut oil (Peanut oil): From groundnuts, widely used for cooking.
Coconut oil: From the kernel of coconuts.
Shea butter: From the nut of the shea tree (common in Northern Nigeria, used in cosmetics and food).
Soybean oil: From soybeans.
Sunflower oil: From sunflower seeds.
Olive oil: From olives.
Vegetable margarine: Produced by hydrogenation of vegetable oils. The primary distinction between fats and oils lies in their physical state at room temperature (around 25°C) and their chemical composition regarding saturation. | Feature | Fats | Oils | | :------------------ | :----------------------------------- | :------------------------------------- | | Physical State | Solid at room temperature | Liquid at room temperature | | Saturation | Predominantly contain saturated fatty acids (no C=C double bonds). | Predominantly contain unsaturated fatty acids (one or more C=C double bonds). | | Melting Point | Generally high melting points | Generally low melting points | | Sources | Mostly animal sources (e.g., butter, lard, tallow), but some plant sources like cocoa butter also exist. | Mostly vegetable sources (e.g., palm oil, groundnut oil, olive oil), but some animal sources like fish oil also exist. | | Stability | More stable, less prone to rancidity | Less stable, more prone to rancidity due to reactive C=C bonds |
Example: Palm oil is a liquid oil at typical Nigerian room temperatures, but it solidifies if refrigerated due to its relatively high proportion of saturated fatty acids compared to other vegetable oils like groundnut oil.
However, it's still classified as an oil because its melting point is usually below 25°
C. Physical State: Fats are solid at room temperature, while oils are liquid at room temperature.
Solubility: They are insoluble in water (hydrophobic) but readily soluble in organic solvents such as ether, chloroform, benzene, and warm ethanol. This property is due to their large non-polar hydrocarbon chains.
Density: They are less dense than water (float on water). Their density is typically around 0.9 g/cm
3. Taste and Odour: Pure fats and oils are tasteless and odourless.
However, they often acquire characteristic tastes and odours from impurities or decomposition products (e.g., rancidity).
Non-volatility: They have very high boiling points and are non-volatile, meaning they do not evaporate easily at room temperature.
Colour: Varies depending on the source and processing. For instance, crude palm oil is reddish-orange due to carotenes, while refined oils are pale yellow or colourless.
Hydrolysis: This is the reverse of esterification, where fats/oils react with water to break down into glycerol and fatty acids.
Acid Hydrolysis: Requires heating with dilute mineral acids (e.g., H2SO4 or HCl) as a catalyst. This is a reversible reaction. ``` CH2-O-CO-R1 CH2-OH | | CH-O-CO-R2 + 3H2O (H+, Heat) ⇌ CH-OH + R1-COOH + R2-COOH + R3-COOH | | CH2-O-CO-R3 CH2-OH (Triglyceride) (Glycerol) (Fatty Acids) ``` Enzymatic Hydrolysis: Catalysed by enzymes called lipases (found in digestive systems). This occurs under mild conditions (body temperature, neutral pH).
Alkaline Hydrolysis (Saponification): This is a special type of hydrolysis discussed in detail below.
Hydrogenation (Hardening of Oils): This is the process of converting unsaturated oils into saturated fats by adding hydrogen atoms across the C=C double bonds in the presence of a catalyst (e.g., finely divided nickel or platinum) and heat (140-200°C) and pressure.
Purpose: To convert liquid oils into solid or semi-solid fats, increasing their melting point and stability. This process is used in the manufacture of margarine and vegetable ghee from oils like groundnut oil or palm kernel oil. ``` -CH=CH- (in oil) + H2 (Ni catalyst, Heat) → -CH2-CH2- (in fat) ```
Example: Conversion of triolein (an unsaturated oil, main component of olive oil) to tristearin (a saturated fat). ``` O O || || CH2-O-C-(CH2)7-CH=CH-(CH2)7-CH3 CH2-O-C-(CH2)16-CH3 | | CH-O-C-(CH2)7-CH=CH-(CH2)7-CH3 + 3H2 (Ni, Heat) → CH-O-C-(CH2)16-CH3 | | CH2-O-C-(CH2)7-CH=CH-(CH2)7-CH3 CH2-O-C-(CH2)16-CH3 (Triolein - an oil) (Tristearin - a fat) ``` Halogenation: Unsaturated fats and oils can react with halogens (like bromine or iodine) by addition across the double bonds. Saturated fats and oils do not undergo this reaction. This property is used to determine the iodine value of a fat or oil, which indicates the degree of unsaturation. A higher iodine value means more double bonds are present, thus it's more unsaturated. ``` -CH=CH- (in oil) + Br2 → -CH(Br)-CH(Br)- ``` Rancidity: This refers to the deterioration of fats and oils, resulting in an unpleasant smell and taste. It primarily occurs in unsaturated fats and oils due to: Oxidative Rancidity: Reaction of unsaturated fatty acids with atmospheric oxygen, catalysed by light, heat, or enzymes. This breaks down the fatty acids into short-chain aldehydes and ketones, which have foul odours.
Hydrolytic Rancidity: Hydrolysis of the ester bonds, releasing free fatty acids (e.g., butyric acid in butter), which can have unpleasant odours.
Prevention: Storage in cool, dark places; addition of antioxidants (e.g., Vitamin E, BHT, BHA); hydrogenation; vacuum sealing.
Nigerian Cuisine and Health Implications: Fats and oils are central to Nigerian cooking. Palm oil is a staple, used in soups, stews, and frying. Groundnut oil and soybean oil are also widely consumed. This topic helps students understand the nutritional value (energy source, fat-soluble vitamins) and potential health implications of different types of fats (e.g., saturated fats in animal products and their link to cardiovascular health vs. unsaturated fats in vegetable oils). Discussions can extend to balancing local diets for optimal health.
Local Industry and Traditional Crafts: The production of palm oil and shea butter are significant local industries in many parts of Nigeria. Students can learn about the extraction processes and the economic importance of these products. Saponification directly links to traditional soap-making practices in communities, where local oils are converted into laundry or body soaps, often by women cooperatives, providing income and sustainable products.
Food Preservation and Shelf Life: The concept of rancidity is highly relevant in a country where refrigeration might not always be readily available. Understanding how fats and oils spoil helps students appreciate methods of food preservation in Nigerian homes and markets (e.g., storing palm oil in dark, cool places; adding spices that might have antioxidant properties). It connects chemistry to everyday challenges of food storage and waste reduction. ---