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Fats and Oils: Soaps and Detergents

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Exercise No. 10



• To examine properties of fats and oils

• To prepare a sample of soap and to examine its properties.


A. Solubility


Cottonseed oil Lard

Water Insoluble Insoluble

Alcohol Slightly soluble Slightly soluble

D. The Preparation of Soap

Tests Performed Soap (brand x) Soap

(a)Alkalinity Red litmus paper to blue (Basic) Red litmus paper to blue (Basic)

(b)CaCl2 solution Precipitate formed Precipitate formed

MgCl2 solution Precipitate formed Precipitate formed

FeCl3 solution Precipitate formed Precipitate formed

. (d)Emulsifying action of soap

Soap solution + Palm oil = oil dissolved

Water + Palm oil = formed an immiscible layer 


Fats and Oils are organic compounds; complete esters of glycerol (triglycerides) and monobasic fatty acids. They belong to the lipid class along with carbohydrates and proteins. Fats and oils are one of the main components of the cells of animals, plants, and microorganisms and both have the general formula:




Fat is one of the three main macronutrients: fat, carbohydrate, and protein. They are a wide group of compounds whose basis is in long-chain organic acids, called fatty acids. Most common fatty acids ranges in size from 10-20 carbons most often have an even number of carbon atoms including the carboxyl group carbon. Particularly, fats are esters of such organic acids formed with the alcohol glycerol. Glycerol is a triol, meaning that it has three chemically active -OH (hydroxyl) groups (HOCH2CHOHCH2OH). Fats are made when each of these three -OH groups reacts with a fatty acid and is classified as solid or semi-solid at ordinary temperature. The resulting fats are called triglycerides with the formula shown above. Oil is the term usually used to refer to fats that are liquids at normal room temperature.

In the first part of the experiment, solubility of sample of oil and fats in water and alcohol were examined. When Cottonseed oil and lard were added separately to water, immiscible layer formed or simply both did not dissolve to water. Oil is any neutral, non-polar chemical substance and is hydrophobic which is immiscible in water or literally “water-fearing”. As a rule of thumb, like dissolves like. Because oils are non-polar and water is polar that’s why oils did not dissolve in water. The same as with oils, fats are non-polar carbon-hydrogen bonds in the tails of fatty acids and are highly hydrophobic. As a result the fat molecules do not interact well with water molecules, so they are 'repelled' by the water and do not dissolve. Also Fats have lesser specific gravity than water. Both fats and oils are slightly soluble when added to alcohol because both fats and oils are slightly soluble in organic solvent.

Preparation of soap was also done in this experiment. Soaps are carboxylate salts, usually a sodium or potassium salt of a long‐chain fatty acid. Most solid soaps are sodium salts which was the type that made in this experiment whereas liquid soaps consist of the potassium salts of fatty acids. The starting materials are fats or oils, which are the glycerol esters of the fatty acids, or a typical cooking oil and a concentrated solution of sodium hydroxide. Ethanol is used in this experiment to serve as a common solvent for the reactants and hence speed up the reaction. The soap‐making process is called saponification- the alkaline hydrolysis of fats and oils. An example of a saponification reaction is shown below.

fat or oil glycerol soaps

Test for Alkalinity

In the experiment, the prepared soap was tested using red litmus paper and its color turned into color blue which indicates that the prepared soap was basic. Because soaps are salts of strong bases and weak acids, they should be weakly alkaline in aqueous solution. However, soap with free alkali can cause damage to skin, silk, or wool. Therefore, a test for basicity or alkalinity of the soap is quite important.

Metallic Salts of Fatty Acids

In the experiment, soap solution was added by Calcium chloride (CaCl2) and a precipitate was observed. Magnesium chloride (MgCl2) and Ferric chloride (FeCl3) solutions also observed to produce precipitate. Soaps will react with metal ions in water and can form insoluble precipitates. The precipitates can be seen in the soapy water and are

referred to as “soap scum”. A reaction of soap and metal ions is shown below:

2 CH3(CH2)16CO2-Na+ + M2+ [CH3(CH2)16CO2-]2M2+ ↓ + 2 Na

Soap Scum

M= (Ca2+ or Mg2+)

Although soap is a good cleaning agent, its effectiveness is reduced when used in hard water. Hardness in water is caused by the presence of mineral salts, mostly those of Calcium (Ca) and Magnesium (Mg), but sometimes also Iron (Fe) and manganese (Mn). Since soap forms a precipitate with these ions, it means that many of the soap molecules are no longer present in the solution. This precipitate which is called as scum as mentioned earlier does not rinse away easily. It tends to remain behind and produces visible deposits on clothing and makes fabrics feel stiff. It also attaches to the insides of bathtubs, sinks and washing machines.


The hydrocarbon end of soap is nonpolar and is soluble in nonpolar substances such as fats and oils, and the



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