Saponification Flashcards
what is the basic/general formula for saponification?
fat/oil + base –> glycerol + salt (soap)
What are most oils and fats?
tryglicerides
What is an example of saponifcation?
glycerol tristearate + sodium hydroxide
————>
glycerol + sodium stearate
what is the chemical formula for sodium stearate?
CH3-(Ch2)16COO-Na+ (aq)
What are the steps to carry out saponification and test the product (at school)?
- Pour 30ml 5molL-1 NaOH solution into a 250ml beaker. Add 10ml of coconut oil
- Gently boil mixture for 20-30min, stirring occasionally. Add 20ml NaCl solution (Causes soap to precipitate). Allow solution to cool (clumps of soap should begin to form)
- Filter out the crude soap and rinse with a little water.
- test the soap by shaking a small amount in a test tube with water to see if it lathers.
Summise saponification in school laboratory
reasonably pure oil is added to NaOH and NaCl solution.
- the soap is precipitated with NaCl and is filitered
- It is then rinsed to remove NaOH, glycerol and salt
Saponification was performed on a small scale
Summise saponification in industry
- Concentrated NaOH and impure fats and oils are mixed in larger quantities and stirred using steam and pressure.
- Precipitation is caused by adding salt and the glycerol that is filtered off is used for other industrial processes
What are the similarities between the saponification in a school laboratory compared to inindustry
- fats and oils are mixed with a concetrated alkali and heated
- Concentrated brine is used to precipitate the soap from the aqueous phase
- the crude soap is washed
What are the differences between the saponification in a school laboratory compared to inindustry
- A blend of gnerally impure fats & oils are used in industry, rather than one pure fat or oil in the lab
- High pressure steam is used to heat & stir the mixture in industry, whereas a glass rod and hot plate are used in the laboratory
- The glycerol is removed and purified for other use in industry, where as in the lab glycerol is discarded and some remains in the soap
- in industry the settling of soap occurs over several days –> in lab soap is relatively crude and collected rapidly
- In industry some old soap and salt is left in the kettle to emulsfiy new reactants –> in lab methylated spirits is added to help emulsification
- no fragrances or colours were added to the soap produced in the laboratory
-A blend of gnerally impure fats & oils are used in industry where as in the lab?
one pure fat or oil in the lab
a glass rod and hot plate are used in the laboratory where as in industry?
High pressure steam is used to heat & stir the mixture in industry
The glycerol is removed and purified for other use in industry, where as?
in the lab glycerol is discarded and some remains in the soap
in lab soap is relatively crude and collected rapidly where as?
in industry the settling of soap occurs over several days
in the lab methylated spirits is added to help emulsification, where as?
In industry some old soap and slat is left in the kettle to emulsfiy new reactants
in industry fragrances or colours are added where as?
-no fragrances or colours were added to the soap produced in the laboratory
Safety precautions for saponification in lab?
As working with moderately conc. NaOh it is important to
The soap produced may have unreacted NaOH
What is the nature of a soap molecule like sodium stearate?
-has a small hydrophylic head and a long hydrophobic tail
hydrophylic head and a long hydrophobic tail
hydrophylic head loves water (just the COO- part), because it is POLAR and dissolves in water readily
the hydrophobic tail hates water because its a non-polar hydrocarbon and won’t dissolve in water. Instead it dissolves dirt or grease (generally non-polar)
What is a micelle?
when grease is surrounded by soap molecules with their tail dissolved in the grease and their head dissolved in the water!
How does soap (sodium stearate) remove dirt?
it removes dirt with the aid of water. This is achieved because:
- dirt/grease is generally non-polar, thus the non-polar tail of the soap dissolves it
- the polar head dissolves in water
- the formation of a micelle is then lifted off the skin upon agitation and is washed away with the water
What is an emulsion?
a mixture of one liquid dispersed in tiny drops through another liquid
Explain that soap, oil and water together form an emulsion
the longer hydrocarbon chains of the soap dissolve in the oil droplets, with the charged heads remainng attracted to the water molecules
-this creates micelles which are dispersed throughout the mixture (water), with the change in surface properties of the oil droplets keeps the emulsion stable
How does soap act as an emulsifier?
by allowing small amounts of oil to break up into small droplets, remaining suspended in the water.
-Soap forms a layer between the tiny oil droplet and the water
What is an anionic detergent
the same as sodium stearate but instead of the COO- head there is a ‘sulfonoate’ head SO3-.
- This detergent removes dirt better than soap, but produces a lot of froth
What are uses of an anionic detergent?
- washing up liquid
- laundry detergent
- (too harsh for use on skin!)
What is a cationic detergent?
the same as sodium stearate but the head has been replaced with a compound based on NH4+, making the head positive
What are uses of cationic detergent?
- conditioners
- fabric softeners
What is a non-ionic detergent?
the same as soap but the head is not an ion, but a polar OH- group and special ester links (C-O-C)
-produce little lathering
What are uses of non-ionic detergents?
-dish-washer detergents and some shampoos
what is the difference in the chemical composition between soaps and detergents?
soap- made from fatty acids in animal and vegetable oils
detergents -hydrocarbon made from petroleum
what is the difference in the structure of the molecule between soaps and detergents?
soaps -have an ioninc/polar head and a long, non-polar hydro carbon tail. They are anionic**
-detergents- similar structure, polar head, and non polar tail.
may be anionic, cationic or non-ionic
What is the effect of soap in hard water?
- it doesn’t lather well in hard water
- soap anions precipitate with the cations in hard water.
Ca2+ annd Mg2+ form a precipitate (scum) with the stearate anion
-this reduces the cleaning ability
What is the effect of detergents in hard water?
-detergents lather in hard water and don’t precipitate minerals in hard water
What are the environmental impacts of soaps and detergents?
- soap have little/no enviro impact (only aesthetic pollution of froth)
- consist of unbranched hydrocarbon tail made up of natural fats and oils –>biodegradable
-this means that bacteria can rbeak them down into simple substances such as water and CO2
What are the environmental impacts of detergents?
- early detergents in 1950s and 60s werent biodegradable as they consisted of branched chains and aromatic rings eg. sulfanoate.
- This caused considerable enviro impact as these synthetic surfactants caused excessive foaming when discharged into rivers and lakes
- this effected appearance and health of river, with the foam blanket preventing oxygen and other gases from freely dissolving in water
-recent detergents are biodegrabdale due to unbranched hydrocarbon chain tail
detergents can have ‘builders’ added which are high in phosphate, which can contribute to eutrophication.
- thus modern detergents despite being biodegradable can have a major impact on enviro
- *cationic detergents can be dangerous if large amounts are released as they possess biocidal properties which can kill useful bacteria in treatment plants (sewage)
