Fats and Oils: Soaps and Detergents

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ionic end which is the salt of a carboxylic acid is soluble in water. A sample structure of a soap molecule is represented below:

O

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CH3-CH2-CH2- CH2-CH2-CH2-CH2- CH2-CH2- CH2-CH2- CH2-CH2- CH2-CH2- C-O− Na+

Non-polar hydrocarbon chain ionic end

(soluble in nonpolar substances) (soluble in water)

Soap can emulsify fats and oils by forming micelles around oil droplets. The soap molecules surround an oil droplet so that their nonpolar tails are embedded in the oil and their charged “head” groups are on the exterior of the droplets, facing the water. If the oil droplets are small enough and if there are enough soap molecules to surround them, the oil droplets become dispersed in the water and can then easily be washed away, this is referred as emulsification. That’s why in the experiment, palm oil dissolved in soap solution because soap act as an emulsifying agent.

IV. CONCLUSION:

Therefore, by this experiment properties of fats and oils were examined. Fats and oils are insoluble in water because both are non-polar and water is polar. As a rule of thumb, like dissolves like, thus non-polar compounds dissolve in non-polar solvent and polar compounds dissolve in polar solvent like water. Preparation of soap was also done in the experiment by the reaction of a fat or oil with Sodium hydroxide. There were also some tests done to know some of its properties. Soap solutions are basic. When they are added to solutions containing metallic salts like CaCl2 and MgCl2, they formed precipitates called as scum. Soaps also act as an emulsifying agent which can remove grease and oil.

V. ANSWERS TO QUESTION

1. Draw formulas and give names for glycerides which probably are present in lard, in Mazola oil

Palmitic acid CH3(CH2)14COOH

Stearic acid CH3(CH2)16COOH

Oleic acid CH3(CH2)7CH=CH(CH2)7COOH

Lauric acid CH3(CH2)10COOH

Myristic acid CH3(CH2)12COOH

2. Could cottonseed oil be used in paints as drying oil?

It would not be suitable as paint or a coating because it is essentially classified as a semi-drying or non-drying oil.

3. Assume that the average molecular weight of a fat is 890g/mol. What fatty acid components probably predominate?

Glycinyl tristearate C3H5(C18¬H35O2)3

CH2 O COCH3(CH2)16

CH O COCH3(CH2)16

CH2 O COCH3(CH2)16

4. Why was dilute soap solution poured in a solution of sodium chloride in water?

This is to allow soap to precipitate out of the solution. Initially, the soap is barely held in the solution by the charges from the polar water molecules

5. How does soap function as an emulsifying agent for oil in water? Draw picture of an oil droplet and several soap molecules to illustrate your answer.

Because "like dissolves like’ the nonpolar end (hydrophobic or water-hating part) of the soap molecule can dissolve the greasy dirt, and the polar or ionic end (hydrophilic or water-loving part) of the molecule is attracted to water molecules. Therefore, the dirt from the surface being cleaned will be pulled away and suspended in water. Thus soap acts as an emulsifying agent, a substance used to disperse one liquid (oil molecules) in the form of finely suspended particles or droplets in another liquid (water molecules).

A diagram of a soap micelle surrounded by water

molecules. The lines in the centerrepresent grease and oil.

6. Suppose that you wanted to emulsify a water-insoluble compound in water. Would soap be a reasonable choice for the emulsifying agent if the water were slightly acidic? Why? Ir it would be not a good choice, can you draw the structure of an organic molecule that might be more suitable?

In the basic sense, soap will be more or less ineffective on acidic solutions. Thus it would not serve as an emulsifying agent because of the acidic conditions changes the soaps into carboxylic acid and the cleaning action of the soap becomes ineffective overall. Synthetic detergents, also known as “soapless soaps” was developed that proved effective in hard water and salt water because they do not produce scum. Some detergents are of sulphonate group (SO3-Na) or a Sulphate group (-OSO3-N+)

Some structures are shown below;

a sodium alkyl sulfate

a

a sodium alkylbenzene sulfonate

7. If castor oil were treated by sulfuric acid and then neutralized with sodium hydroxide, what would probably be the result? Would this structure be water-soluble?

The product of sulfonation of castor oil after neutralization is essentially water soluble oil that is used in cosmetics. The product is considered as the first synthetic detergent which is named as Turkey red oil. It is also used in the textile industries, used in soap industries as soap defoaming agent and as an emulsifier.

8. Saponification (conversion into soap) is a term used to describe the alkaline hydrolysis of any ester. Why is alkaline hydrolysis of an ester to be preferred over acid hydrolysis?

Alkaline hydrolysis proceeds in only one direction and most important of all is the fact that the products can be separated easily. Distillation would get rid the alcohol formed and reacting the carboxylate salts with Hydrochloric acid or Sulfuric acid to get the respective carboxylic acids