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Chemistry

Fats and Oils

Fats and Oils

Fats and oils are naturally-occurring esters of three long carboxylic acids  called fatty acid with a special type of alcohol called glycerol ( propane- 1,2,3-triol). Glycerol has three carbon atoms, each with an –OH group on. These fats and oils belong to a group of compounds called lipids.

Fats are solid at room temperature, whereas oils are liquids. Animals and plants produce oils and fats as an energy store. Fats and oils are the most abundant lipids in nature. They provide energy for living organisms, insulate body organs, and transport fat-soluble vitamins through the blood.

Structures of Fats and Oils

Fats and oils are called triglycerides because they are esters composed of three fatty acid units joined to glycerol, a trihydroxyl alcohol:

faats and oil

Saturated and Unsaturated Fats and oils

Fatty acids can be saturated or unsaturated

The saturated fatty acids have single bond in their hydrocarbons while the unsaturated ones have double bonds. Esters produced from saturated fatty acids are usually solids at room temperature and they are called fats while the esters produced from unsaturated fatty acids are liquids at room temperature and are called oils.

Sources of Fats and Oils

  • Animal sources generally provide fats, for example, dripping from beef, lard from pork and tallow from lamb. These fats are solid at room temperature and only become liquid when heated.
  • Vegetable sources generally provide oils. Ester oils can be obtained from olives and seeds such as corn seed, sunflower seed, peanuts and soya beans, liquids at room temperature.
  • Marine sources can provide both fats and oils, Sea mammals providing fats and oils being obtained from fish.

Properties of Fats and Oils

  1. Both fats and oils are insoluble in water and they decompose at temperature above 300oC.
  2. Since they are esters their main reactions are saponification and hydrolysis.

Uses of Fats and Oil

  1. Fats and oils are used as essential ingredients of food
  2. Sometimes they are used in natural form such as groundnut oil, palm oil for such industrial products as margarine
  3. They are used as raw materials for making soap e.g. palm oil and coconut oil
  4. They are used in making paint, candles and varnishers

Hydrolysis of Fats and Oils

Fats and oils contain ester links formed when glycerol has reacted with fatty acids. These ester links can be broken when they react with water, splitting the molecule back into an acid and an alcohol.

This process is known as hydrolysis of an ester. It can be described using the following word equation:

ester + water → acid + alcohol

Hydrogenation of Oils

The hydrogenation of oils is also known as hardening of oil. This is done by passing hydrogen into unsaturated oil at about 180oC and 5 atmosphere of pressure and in the presence of finely divided nickel as catalyst. In the process, the unsaturated part of the oil is saturated and the oil becomes hardening into fat.

Margarine is made by mixing such hardening oils with vitamins, salt, skimmed milk and colouring materials.

Formation of Soap (Saponification)

Saponification is a process by which triglycerides are reacted with sodium or potassium hydroxide to produce glycerol and a fatty acid salt, called ‘soap’. In other word, Saponification is the alkaline hydrolysis of the fatty acid esters.

Natural soaps are sodium or potassium salts of fatty acids, originally made by boiling lard or other animal fat together with lye or potash (potassium hydroxide). Hydrolysis of the fats and oils occurs, yielding glycerol and crude soap.

In the industrial manufacture of soap, tallow (fat from animals such as cattle and sheep) or vegetable fat is heated with sodium hydroxide. Once the saponification reaction is complete, sodium chloride is added to precipitate the soap. The water layer is drawn off the top of the mixture and the glycerol is recovered using vacuum distillation. Dyes, perfumes and disinfectants are added as required before the soap is passes into bars.

Detergents

Detergents are substances which act with water to make things clean. The can be conveniently classified into two main types – soapy and soapless detergents

Soapy Detergents: are detergents made from soap. They are made by heating vegetable oils like palm oil with a strong alkali like sodium hydroxide. Soap is also biodegradable, i.e. it can easily be decomposed by bacteria into simple inorganic substances.

Soapless Detergents: Most of the soapless detergents are made from petroleum fractions. Usually the hydrocarbon is reacted with sulphuric acid, and the product neutralized with sodium hydroxide to obtain the soapless detergent. They are non-biodegradable and so create water pollution problems when their forms clog up waterways.

Detergent helps to remove dirt in different ways:

1.)  They help water to spread out and completely soak a surface. They are good wetting agents.

2.)  They form an emulsion with the dirt. They are emulsifying agents.

3.)  As a wetting agent, detergent help to reduce the surface tension of water, which tends to pull water molecules together and making water itself to be a bad wetting agent.

As an Emulsifying Agent

Detergent has two main parts;

  1. A long hydrocarbon chain which is soluble in the grease or oil of the dirt. This part is not soluble in water and described as hydrophobic
  2. An ionic or polar part which in not soluble in the dirt but is soluble in water. This part is described as hydrophilic, COONa+or COO K+

Mode of Action

When detergent is added to grease, the grease soluble hydrophobic tail dissolve in the grease and the hydrophilic parts that bring along with a negative charge are insoluble in the grease and so they remain outside. The surface of the grease becomes negatively charge, and if stirring is applied, very large of colloidal particles of grease and detergent are formed. They are held in aqueous solution by the attraction of the hydrophilic parts for the water molecules, but are prevented from coming together because similarly charged on surface of the particles cause repulsion between each other. Thus they form an emulsion of dirty water.

Differences between Soaps and Soapless Detergent

1) Soap from scum with hard water (which contains dissolve calcium or magnesium ions), while soapless detergent is not affected.

2) Soaps are made from edible animal or vegetable oils while soapless detergents are made from petroleum, which is cheaper and edible.

ASSESSMENT (POST ANSWERS BELOW USING THE BOX)

  1. ……… is a process by which triglycerides are reacted with sodium or potassium hydroxide to produce glycerol and a fatty acid salt, called ‘soap’.
  2. Fats are ……. at room temperature.
  3. ……… are substances which act with water to make things clean
  4. Mention 4 sources of fats and oil

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