chemistry folio- soap and detergent
TRANSCRIPT
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
MEANING OF SOAP
• General formula:
RCOOˉNa+ or RCOO ˉK+
• Example:
Sodium palmitate, CH3(CH2)14COO-K+
Potassium stearate, CH3(CH2)16COO-K+
SOAP PREPARATION PROCESS
• Soaps are prepared by the alkaline hydrolysis of fats and oils. This process is known as saponification.
• 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.
Oil or fat Alkali Glycerol Soaps
۞ Saponification is the alkaline hydrolysis of ester using alkali solutions
DETERGENT PREPARATION PROCESS
Preparation of sodium alkyl sulphate:• Step 1: Reaction with concentrated sulphuric acid
• Step 2: Neutralisation with sodium hydroxide solution.
Preparation of sodium alkylbenzene sulphonate• Step 1 : Alkylation
• Step 2 : Sulphonation
• Step 3 : Neutralisation
۞Alkylation is the introduction of the alkyl group to an organic molecule
۞Sulphonation 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.
EFFECTIVENESS OF THE CLEANSING ACTION OF SOAP AND DETERGENT
Characteristic Soap Detergent
Cleansing ability Weaker Stronger
Rinsing ability difficult to rinse completely. Soap that is left behind damages the material
Rinses easily and completely out of clothes and other objects.
Molecular structure It can only be determined by the structure of the fatty acid used to produce soap
It can be modified to suit the job of cleaning. For example, the formula of 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
ADDITIVES USED IN DETERGENT AND THEIR RESPECTIVE FUNCTIONS
Additives Function
Biological enzymes (amylase, lipase, protease)
Break down fat and protein molecules in food stains to produce fatty acids, glycerol and amino acids that are soluble in water, thus increase the cleansing power of a detergent
Whitening agents (sodium perborate)
Remove stains, clothes become white and cleaner
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 sulphate, sodium silicate)
Ensure that the detergent in powdered form is always in a dry condition
Stabilisers Prevent the formation of foam
Perfumes Make clothes smell fresh and [email protected]
