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Yr 12 Chemistry > Saponification > Flashcards

Saponification Flashcards

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1
Q

what is the basic/general formula for saponification?

A

fat/oil + base –> glycerol + salt (soap)

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2
Q

What are most oils and fats?

A

tryglicerides

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3
Q

What is an example of saponifcation?

A

glycerol tristearate + sodium hydroxide
————>
glycerol + sodium stearate

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4
Q

what is the chemical formula for sodium stearate?

A

CH3-(Ch2)16COO-Na+ (aq)

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5
Q

What are the steps to carry out saponification and test the product (at school)?

A
  1. Pour 30ml 5molL-1 NaOH solution into a 250ml beaker. Add 10ml of coconut oil
  2. 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)
  3. Filter out the crude soap and rinse with a little water.
  4. test the soap by shaking a small amount in a test tube with water to see if it lathers.
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6
Q

Summise saponification in school laboratory

A

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

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7
Q

Summise saponification in industry

A
  • 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
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8
Q

What are the similarities between the saponification in a school laboratory compared to inindustry

A
  • 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
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9
Q

What are the differences between the saponification in a school laboratory compared to inindustry

A
  • 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
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10
Q

-A blend of gnerally impure fats & oils are used in industry where as in the lab?

A

one pure fat or oil in the lab

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11
Q

a glass rod and hot plate are used in the laboratory where as in industry?

A

High pressure steam is used to heat & stir the mixture in industry

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12
Q

The glycerol is removed and purified for other use in industry, where as?

A

in the lab glycerol is discarded and some remains in the soap

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13
Q

in lab soap is relatively crude and collected rapidly where as?

A

in industry the settling of soap occurs over several days

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14
Q

in the lab methylated spirits is added to help emulsification, where as?

A

In industry some old soap and slat is left in the kettle to emulsfiy new reactants

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15
Q

in industry fragrances or colours are added where as?

A

-no fragrances or colours were added to the soap produced in the laboratory

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16
Q

Safety precautions for saponification in lab?

A

As working with moderately conc. NaOh it is important to

The soap produced may have unreacted NaOH

17
Q

What is the nature of a soap molecule like sodium stearate?

A

-has a small hydrophylic head and a long hydrophobic tail

18
Q

hydrophylic head and a long hydrophobic tail

A

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)

19
Q

What is a micelle?

A

when grease is surrounded by soap molecules with their tail dissolved in the grease and their head dissolved in the water!

20
Q

How does soap (sodium stearate) remove dirt?

A

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
21
Q

What is an emulsion?

A

a mixture of one liquid dispersed in tiny drops through another liquid

22
Q

Explain that soap, oil and water together form an emulsion

A

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

23
Q

How does soap act as an emulsifier?

A

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

24
Q

What is an anionic detergent

A

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

25
Q

What are uses of an anionic detergent?

A
  • washing up liquid
  • laundry detergent
  • (too harsh for use on skin!)
26
Q

What is a cationic detergent?

A

the same as sodium stearate but the head has been replaced with a compound based on NH4+, making the head positive

27
Q

What are uses of cationic detergent?

A
  • conditioners

- fabric softeners

28
Q

What is a non-ionic detergent?

A

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

29
Q

What are uses of non-ionic detergents?

A

-dish-washer detergents and some shampoos

30
Q

what is the difference in the chemical composition between soaps and detergents?

A

soap- made from fatty acids in animal and vegetable oils

detergents -hydrocarbon made from petroleum

31
Q

what is the difference in the structure of the molecule between soaps and detergents?

A

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

32
Q

What is the effect of soap in hard water?

A
  • 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

33
Q

What is the effect of detergents in hard water?

A

-detergents lather in hard water and don’t precipitate minerals in hard water

34
Q

What are the environmental impacts of soaps and detergents?

A
  • 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

35
Q

What are the environmental impacts of detergents?

A
  • 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)

Yr 12 Chemistry (11 decks)

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