Ch. 5 - Saponification Flashcards
Identify a range of fats used in soap making
LARD is derived from pig fat - Produces hard soap - High % of oldie acid, and relatively high percentage of very long chain saturated fatty acids (eg palmitic and stearic acid) TALLOW is derived from beef, or sheep, processing - Produces hard, greasy soap unless other oils such as coconut oil are blended with it before alkaline hydrolysis - High percentage of oleic acid, and a relatively high percentage of very long chain saturated fatty acids
What is saponification?
Saponification is the hydrolysis conversion in basic solution of fats and oils to glycerol and salts of fatty acids
Identify a range of oils used for soap making
OLIVE OIL - Has a very high percentage of unsaturated fatty acids (mainly oleic) COCONUT OIL is derived from pressed, dried fruit of coconut palm - often blended with tallow to produce a softer soap that dissolves faster in water - produces soaps that another in salty or hard water PALM OIL - has long hydrocarbon chains, and thus properties are more similar to tallow than vegetable oils
Describe the conditions under which saponification can be performed in the school laboratory
- At school, the cold process is used with coconut fat and Castor oil, since it forms a relatively hard soap that is easy to extract
- The relatively pure fat/oil is mixed with excess sodium hydroxide solution when both mixtures are 35°C - hot plate and manual stirring
- The soap is poured into trays or moulds and left for 2 days
- The mould is then unwrapped and cut up into bars, and left for 3-4 weeks for it to cure
- Glycerol remains in the final soap product
Describe the properties of butter and relate them to its uses
- Butter is a oil in water emulsion
- Can be spread onto food surfaces without wetting it
- Butter is stabilised by milk proteins as an emulfiser,
- Coverage of food surface is smooth rather than patchy
- It also remain solid in the refrigerator, and softens to a spreadable consistency at room temperature
- The water in the butter can also dissolve flavourings as well as salt, which enhances flavour and acts as a preservative
- Heating or increasing the pH of butter can also destabilise it so the proteins are no longer an effective emulfiser
- can be readily melted to a thin liquid to prepare sauces
What is a surfactant
A surfactant is a substance that decreases the surface tension of water
Account for the cleaning action of soap by describing its structure
The cleaning action of soap is due to its ionic nature and structure When soap is dissolved in water, the cation (usually Na+ or K+) separates from the fatty carboxylate anion, which consists of a long, hydrophobic hydrocarbon chain called the tail and a hydrophilic carboxylate end group called the head The hydrophobic, non-polar tail readily dissolves in the grease due to dispersion forces, while the hydrophilic, anionic head readily dissolves in water due to ion-dipole interactions Hence the surfactant anion bridges the grease and water, forming a stabilised grease water emulsion with soap as the emulsifier The emulsified grease droplets are covered with the negatively charged head groups of the soap, so they electrostatic ally repel one another and do not combine again and remain dispersed The lather and soapy emulsion of grease and water is then rinsed away, leaving a clean material
How does soap work? (6 steps)
When soap is dissolved in water, the cation (usually Na+ or K+) separates from the fatty carboxylate anion, which consists of a long, hydrophobic hydrocarbon chain called the tail and a hydrophilic carboxylate end group called the head The hydrophobic, non-polar tail readily dissolves in the grease due to dispersion forces, while the hydrophilic, anionic head readily dissolves in water due to ion-dipole interactions Hence the surfactant anion bridges the grease and water, forming a stabilised grease water emulsion with soap as the emulsifier The emulsified grease droplets are covered with the negatively charged head groups of the soap, so they electrostatic ally repel one another and do not combine again and remain dispersed The lather and soapy emulsion of grease and water is then rinsed away, leaving a clean material
What happens first when soap is dissolved in water?
The cation (usually Na+ or K+) separates from the fatty carboxylate anion, which consists of a long, hydrophobic hydrocarbon chain called the tail and a hydrophilic carboxylate end group called the head
Second step in action of soap?
The hydrophobic, non-polar tail readily dissolves in the grease due to dispersion forces, while the hydrophilic, anionic head readily dissolves in water due to ion-dipole interactions
By having the hydrophobic tail attach to oily particles while the hydrophilic head is dissolved in water, what happens?
The surfactant anion bridges the grease and water, forming a stabilised grease water emulsion with soap as the emulsifier
What happens once the oily particles are dispersed in the solution?
The emulsified grease droplets are covered with the negatively charged head groups of the soap, so they electrostatically repel one another and do not combine again and remain dispersed
Describe the chemical composition and uses of anionic detergents
Structure similar to soap, since it has a cation (usually Na+) which in solution separates from the anion, which consists of a long hydrocarbon tail and an anionic head which is a sulfonate
- Its action is the same as soap, except it is a more effective surfactant especially for natural fibres
Also cheap, lathers well and can be dried to a stable powder during manufacture
- Hence it is a major surfactant in general cleaning such as laundry detergents and dishwashing liquids
- Excellent for cleaning glass, since it does not leave a greasy surface
Not suitable for personal hygiene, since it removes too much oil from skin and hair
Generate a lot of foam, which can make it unsuitable for automatic dishwashers and front-loading washing machines
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Diagram of the structure of anionic detergent
Diagram of the structure of cationic detergent
