The free fatty acid is determined by titrating the sample in ethanol with standard aqueous sodium hydroxide using a phenolphthalein indicator solution.
APPARATUS
250 ml
Erlenmeyer Flask
100 ml
Measuring Cylinder
50 ml Burette
REAGENTS
Ethanol 95%
v/v
Phenolphthalein
Indicator Solution, prepared in accordance with Test Method
Preparation of Phenolphthalein Indicator Solution.
0.1M Sodium Hydroxide, prepared in accordance with Test Method.
Standardisation of Sodium Hydroxide Solution
PROCEDURE OF FREE FATTY ACID
Accurately weigh about 10 g of sample into a 250 ml Erlenmeyer flask (gram).Â
Measure 100 ml of ethanol into an 250 ml Erlenmeyer flask, add 1 ml phenolphthalein indicator solution, and titrate to a faint pink colour with 0.1M sodium hydroxide.Â
If the ethanol is already
alkaline to phenolphthalein, add sufficient 0.1M hydrochloric acid to dissipate
the pink colour and then titrate with 0.5M sodium hydroxide to a faint pink
colour.
Add the neutralised ethanol to the Erlenmeyer flask containing the sample, warm and swirl to dissolve the sample.Â
Titrate with 0.1M sodium hydroxide to a faint
pink colour (V).
What is the Difference Between Saturated and Unsaturated Fatty Acids?
CALCULATION OF FREE FATTY ACID
where V is
the volume of NaOH
M NaOH is the
molarity of the NaOH
M Fatty Acid
is the molar mass of the fatty acid
Calculate
the result as Palmitic Acid, M = 256.43 g/mole. Calculate the result as lauric
acid, M =200,32 g/mole ,m is the mass of sample
DETERMINATION OF IODINE VALUE by Fatty Acid Extraction and Titration
The iodine
value of a substance is defined as the weight of iodine absorbed by 100 parts
by weight of the substance. The method determines Iodine Value for soap and
soap noodles.
APPARATUSÂ
Burette
Beaker
Separating
flask
Oven
REAGENTS
Methyl Orange Solution (0.05% w/v).
Ethyl ether.
Sodium
Chloride Solution-saturated.
Acetone.
Sulphuric
acid.
Carbon Tetra-Chloride, A.R grade.
Wij's Iodine Monochloride Solution PreprationÂ
Dissolve 10 ml of Iodine Monochloride in about 800ml of Glacial Acetic Acid and shake vigorously.Â
Store in a glass stoppered bottle in cool place, protected from light.Â
Pipette 5 ml of this, add 10 ml Potassium Iodide solution (10% w/v) and titrate with 0.1 (N) Sodium Thiosulphate solution using starch solution as indicator.Â
Adjust the volume of ths solution till it is 0.2 (N)Â Starch solution.
10% w/v
Potassium Iodide solution.
Sodium Thiosulphate, 0.1(N).
PROCEDURES OF IODINE VALUE
Fatty acid
extraction from soap and soap noodles
4.1 Dissolve
5 gm of the grated sample in 100 ml of distilled water by warming in 250 ml
conical flask on a water bath.
4.2 Add 2 to
3 drops of methyl orange solution (0.05% w/v in alcohol)
4.3 Add
dilute Sulphuric Acid (1:1) till the color changes to pink.
4.4 Insert a
small funnel into the neck of the flask, and heat the flask to a temperature
not exceeding 60 °C until the fatty acids separate as a clear layer.
4.5 Add 50 ml
of saturated sodium chloride solution and cool.
4.6 Transfer
the contents to a separating funnel, draw off the aqueous acid layer into a
second separating funnel and shake it with three 50 ml portions of ethyl ether.
4.7 Dissolve
the fatty acids in the ether used for washing the aqueous liquid and extract
with 10 ml portions of water until the extracts are no longer acidic to methyl
orange indicator.
4.8 Take out
ether layer in a beaker containing anhydrous sodium sulphate.
4.9 Filer it
through a No. 1 Whatman filter paper into a tared beaker.
4.10 Distil
off the ether slowly on a steam bath, and to the residue, add 5 ml of acetone.
4.11 Warm the
beaker on the steam bath at about 90 °C for 10 minutes. Allow to cool the baker
and weigh.
4.12 Return
the flask to the water bath for another 10 minutes, allow to cool, and reweigh.
4.13 Repeat the process until the difference between two consecutive weights is less than 0.005 g.
4.14 Transfer
about 0.3 gm (W, accurately weighed) of the fatty acids obtained in case of
total fatty matter content determination in a dry 250 ml Iodine flask.
4.15 Dissolve
in 25 ml Carbon Tetrachloride, warming if necessary to effect solution.
4.16 Transfer
25 ml of Carbon tetrachloride to a second dry 250 ml Iodine flask.
4.17 Pipette
25 ml of Wij's Iodine monochloride solution into each flask, insert the
stoppers, previously moistened with Potassium Iodide solution (10% w/v KI),
swirl for intimate mixing and allow to stand in a dark place for 30 minutes at
15 to 25 °C.
4.18 Place 15
ml of Potassium Iodide solution in the cup tops, carefully remove the stoppers
and rinse the stoppers and the sides of the flask with 100 ml of water in each
case.
4.19 Shake
and titrate the contents of each flask with 0.1(N) Sodium Thiosulphate, using
starch mucilage added towards the end of the titration, as indicator.
5. CALCULATION OF IODINE VALUE
                                                            1.269 x (V1 - V2)
Iodine value
of the fatty matter = ---------------------
                                                                 W
V1= Volume of
0.1(N) Sodium thiosulphate required for Blank in ml.
V2= Volume of
0.1(N) Sodium thiosulphate required for Sample in ml.
W = Weight of
the sample taken in gm.
