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Soap & Detergent - Coggle Diagram
Soap & Detergent
Detergent
Introduction
A detergent is a non-soapy cleaning agent that uses a surface-active agent (surfactant) for cleaning a substance in solution.
Effective even in hard or salt water, as they form no scum.
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Modern detergents are alkyl or aryl sulphonates produced from petroleum (or coal) and sulphuric acid.
Can be defined as the sodium or potassium salt of sulphonic acid or alkyl hydrogen sulphate that have cleansing properties in water.
Contain one large non-polar hydrocarbon group and one short ionic or highly polar group at each end.
Surfactants
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Containing 8 to 18 carbon atoms, has two different ends. One end is water soluble, called hydrophilic, and the other end is water insoluble, called hydrophobic.
Today, detergent surfactants are made from a variety of petrochemicals (derived from petroleum) and/or oleochemicals (derived from fats and oils).
Surface tension
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All molecules in a liquid are attracted to one another, but on the surface, the attraction is stronger toward the liquid rather than toward the air or whatever is on the surface of the liquid.
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Soap
Introduction
- Soap is a cleaning product made from natural ingredients
- A soap is the metal salt of fatty acid
- In aqueous solution, soap ionises to form alkali ions
- Alkaline in nature & slippery to the touch
Characteristics of soaps
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- Conditioner (emollients) – what’s left behind on your skin after
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Raw Materials
Fats and oils
Long fatty acids always exist as triglycerides and found in fats and oils of animals and vegetable origin.
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- Plant origin: Linseed oil, castor oil, soya bean
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Alkali
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Soluble salt of an alkali metal, were obtained from the ashes of plants.
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Saponification Process
- Definition: Saponification is a process in which esters in fats/oils are hydrolysed with sodium or
potassium hydroxide (lye) to produce a carboxylate anion which can act as a surfactant, i.e. soap.
- Soaps are sodium or potassium salts of long chain fatty acids.
- When triglycerides in fat/oil react with aqueous NaOH or KOH, they are converted into soap (fatty
acid salt) and glycerol (alkaline hydrolysis of esters).
- It is an exothermic chemical reaction that occurs when fats or oils (fatty acids) come into contact
with lye (a base)
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Limitation of Soap
- Soaps do not wash well in hard water and does not form much lather or foam.
- Ordinary soaps are not suited for fabrics such as silks, wool etc. The alkalis in them could
damage the fiber.
- If the water is slightly acidic in nature, soaps cannot be used for cleaning purpose.
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Cleaning Action
When soap dissolves in water, the ions making up the soap dissociate:
RCOO– Na+ (s) → RCOO– (aq) + Na+ (aq)
The negative fatty acid ion is a surfactant (surface acting agent). The positive ion plays no part in cleaning.
The fatty acid anions has a tadpole shaped structure, whose ends have different polarities.
At one end is the long hydrocarbon chain that is non-polar and hydrophobic, i.e., insoluble in water but oil soluble.
At the other end is the short polar carboxylate ion which is hydrophilic i.e., water soluble
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Most dirt is non-polar. Grease consists mostly of long chain, non-polar hydrocarbons.
When grease or oil are mixed with a soap- water solution, the fatty acid anions work as a "bridge" between polar water molecules and non-polar oil molecules.
This action drawing water onto the dirt and fabric. As the water is swirled around it pulls the grease out of the fabric.
The hydrophobic tails dissolve in the greasy dirt and the hydrophilic heads dissolve in water. ☞ micelles are form
Once the dirt and oils are removed from the clothes, surfactants keep them suspended in the water (emulsion) and are washed away with excess of water leaving the fabric clean.
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