Chemistry Folio- Soap And Detergent

Soap and Detergent

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CONTENTS • • • • • •

meaning of soap soap preparation process meaning of detergent detergent preparation process cleansing action of soap and detergent compare and contrast the effectiveness of the cleansing action of soap and detergent • additives in detergent and their respective functions [email protected]

MEANING OF SOAP •

General formula: RCOOˉNa

+

or

RCOO ˉK

• Example: Sodium palmitate, CH3(CH2)14COO-K+ Potassium stearate, CH3(CH2)16COO-K+ [email protected]

+

SOAP PREPARATION PROCESS •

Soaps are prepared by the alkaline hydrolysis of fats and oils. This process is known as saponification.

Oil or fat

•

Alkali

Glycerol

Soaps

A by-product of this reaction is glycerol which is useful as in foods, as an antifreeze, as a tobacco-moistening agent, and in the manufacture of nitroglycerine and dynamite. [email protected]

aponification is the alkaline hydrolysis of ester using alkali solutions

Example:

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MEANING OF DETERGENT

R – OSO3alkyl sulphate ion

alkylbenzene sulphonate ion [email protected]

DETERGENT PREPARATION PROCESS Preparation of sodium alkyl sulphate: • Step 1: Reaction with concentrated sulphuric acid

•

Step 2: Neutralisation with sodium hydroxide solution.

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Preparation of sodium alkylbenzene sulphonate • Step 1 : Alkylation

•

Step 2 : Sulphonation

•

Step 3 : Neutralisation

lkylation is the introduction of the alkyl group [email protected] an organic molecule ulphonation is the introduction of the sulphonic acid group, -SO3H to an organic molecule to form sulphonic acid

CLEANSING ACTION OF SOAP AND DETERGENT • • • •

A piece of cloth with a greasy stain on it, is dipped in a soap or detergent solution. Soap or detergent reduces the surface tension of water. This increases the wetting ability of water. Therefore, the surface of the cloth is wetted thoroughly. The hydrophobic part of the soap or detergent anion dissolves in the grease. The hydrophilic part is attracted to the water molecules. Mechanical agitation during scrubing helps pull the grease free and also break the grease into small droplets. The droplets do not coagulate and redeposit on the surface of the cloth due to the repulsion between the negative charges on their surface. These droplets are suspended in water forming an emulsion. Rinsing washes away these droplets and leaves the surface clean.

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EFFECTIVENESS OF THE CLEANSING ACTION OF SOAP AND DETERGENT Characteristic

Soap

Detergent

Cleansing ability

Weaker

Stronger

Rinsing ability

difficult to rinse completely. Rinses easily and completely out of Soap that is left behind damages clothes and other objects. the material

Molecular structure

It can only be determined by the It can be modified to suit the job of structure of the fatty acid used to cleaning. For example, the formula of produce soap a detergent can be specially made to be able to clean dishes and other utensils only

pH

Alkaline

Can be controlled to suit the type of detergent required

Suspension

Forms scum in hard water

Does not form scum or any other kinds of suspension in hard water

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ADDITIVES USED IN DETERGENT AND THEIR RESPECTIVE FUNCTIONS Additives

Function

Biological enzymes Break down fat and protein molecules in food stains to (amylase, lipase, protease)produce fatty acids, glycerol and amino acids that are soluble in water, thus increase the cleansing power of a detergent Whitening agents (sodium Remove stains, clothes become white and cleaner perborate) Builders (sodium tripolyphosphate)

Soften hard water by removing calcium ions, Ca2+ and magnesium ions, Mg2+, increase the pH value of water

Brighteners

Make fabrics appear white and brighter

Drying agents (sodium Ensure that the detergent in powdered form is always in a dry sulphate, sodium silicate) condition Stabilisers

Prevent the formation of foam

Perfumes

Make clothes smell fresh and clean [email protected]

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