mechanism of working of soap

1. Soaponification
• Ordinary Soap is a simple mixture of sodium
salt of long chain fatty acid.
• Soap made from olive oil is castile soap
• Alcohol is added to make it more transparent
• Perfumes dyes and germicide can be added.
• If Potassium salt is added it is soft soap.
• Soap dispersed in spherical cluster are called
miscelle.

2. A Soap molecule has a polar COONa
end and a non polar end, the long
carbon chain of 12-18 carbons.

3. Miscelle of soap

4. • The polar end is water soluble
[hydrophillic]
• Non polar end is water
insoluble[hydrophobic]
• This are called as amphipathic

5. How do soap clean the dirt
• Water alone cannot dissolve the hydrophobic
substance .
• Oil droplet in contact with water tend to
coalesce [join] so that there is a water and oil
layer.
• But in presence of soap the non polar end of
soap dissolve the oil droplet, leaving the
carboxylate end projecting into the
surrounding water layer.

6. • Repulsion between similar charges keeps the
oil droplet from coalescing; a stable emulsion
of oil and water forms and can be removed
from the surface being cleaned.
• Cleansing property not only limited to
carboxylate salt but is possessed by other
amphiprotic molecule.
How do soap clean the dirt

7. • Hard water contains calcium and magnesium
salt which react with soap to form insoluble
calcium and magnesium carboxylate. [ the ring
in the bath tub]
• A detergent is a surfactant or mixture of
surfactants that has cleaning properties in
dilute solution with water. A detergent is
similar to soap, but with a general structure R-
SO4
-, Na+, where R is a long-chain alkyl group.

9. Analysis of oils and fats
Prepared by
Dr. N.GOPINATHAN
ASSISTANT PROFESSOR
DEPARTMENT OF PHARMACEUTICAL CHEMISTRY
FACULTY OF PHARMACY
SRIHER [DU]
CHENNAI-116
TAMILNADU

10. • Saponification value
• Acid value
• Ester value
• Iodine value
• Peroxide value

11. Determination of saponification value
The saponification value is the
number of milligrams of KOH
necessary to neutralise the free
acids and to saponify the esters
present in 1 g of the substance

12. Why KOH is preferred over NaOH
Potassium hydroxide is also slightly smaller than
sodium hydroxide; therefore, it can penetrate oil
molecules faster than sodium hydroxide, thus
breaking the oil’s hold on surfaces quicker. Since
they are also more soluble, the oils can be
rinsed away easier, especially when using hotter
water or steam equipment

13. TAG + 3KOH---- 3 alkali salt + Glycerol

14. Principle- saponification value
The oil sample is saponified by
refluxing with a known excess of
alcoholic potassium hydroxide
solution. The alkali required for
soaponification is determined by
titration of excess KOH against the
standard HCl

15. Saponification value- apparatus
required
• Erlenmeyer flask
• Round bottomed flask
• Reflux condenser
• Hot water bath / hot plate /
heating mantle.

16. Alcohol distillation
• Reflux 1.2 litre of ethanol with 10 g
of KOH and 6 g of granulated
aluminium or aluminium foil for 30
minutes.
• Distil it and collect 1 litre of ethanol
after discarding first 50 ml.

17. 0.5 m ethanolic KOH
• 30g of KOH in one litre of distilled
alcohol.
• Keep the temperature below 15 C while
dissolving alkali.
• Allow to stand overnight.
• Decant the clear liquid and store it in a
air tight container.

18. Phenolphthalein indicator
Dissolve 1 g of phenolphthaein in 100
ml of rectified spirit.

19. Preparation of 0.5 M HCl
Dilute 42.5 ml of concentrated HCl with water to
produce 1000 ml.

20. Standardisation of o.5M HCl
• Weigh accurately 1.5 g of anhydrous sodium
carbonate previously heated at about 270 C
for one hour.
• Dissolve it in 100 ml of water and add 0.1 ml
of methyl red solution.
• Add 0.5M HCl from burette with constant
swirling.
• Until the solution becomes faintly pink.

21. • Heat the solution to boiling , cool and
continue the titration, Heat again to boiling
and titrate further as necessary until the faint
pink colour is no longer affected by continued
boiling.
• Each ml of 0.5M HCl is equivalent to 0.02649g
of sodium carbonate

22. IP procedure
• Weight of oil mentioned in the individual
monograph otherwise
• Weigh 2 g of sample being examined into a
200 ml flask of borosilicate glass fitted with a
reflux condenser.
• Add 25 ml of 0.5 M ethanolic KOH and a little
pumice powder and boil under reflux on a
water bath for 30 minutes.

23. IP procedure
• Add 1 ml of phenolphthalein solution titrate
immediatley with 0.5 M HCl .
• Repeat the operation omitting the substance
being examined

24. Calculation
• Saponification value = 28.05 x ( b-a )/ w
• W – weight of the sample in grams.
• B- blank
• A- titre value

25. Note
• If the oil purpose of preservation has been
saturated with carbon dioxide for the purpose
of preservation, gently reflux the solution of
the oil in ethanol 95 % and ether for 10
minutes before titration.
• The oil may be freed from the CO2 by
exposing it in a shallow dish in a vacuum
desiccator for 24 hours before weighing the
sample.

26. Significance of Saponification Value
•It gives an idea about the
average molecular weight of the
fat or oil.
Higher the molecular weight
of the fat , the smaller is its
saponification value.

27. Significance of Saponification Value
• It indicates the length of carbon chain of
the acid present in that particular oil or fat.
Higher the saponification value, greater is
the percentage of the short chain acids
present in the glycerides of the oil or fats

28. Significance
• To identify the given fatty oil.
• To distinguish between fatty oils
and mineral oils.
• In detecting the adulteration of
fat or oil.

29. • It also help to calculate the amount
of alkali required to convert a
definite amount of fat or oil into
soap.
• Detection of acids containing less
than 16 carbon or more than 18
carbon.
Significance