PRACTICAL 3: SYNTHESIS AND PROPERTIES OF SOAP
ABSTRACT
In chemistry,
soap is a salt of fatty acid. They occur mainly used as surfactants for
washing, bathing and cleaning but they are also used in textile spinning and
are important components of lubricant. Soap is made of base hydrolysis of
triglycerides. This result in the formation of glycerol and fatty acid salts
which are the soap. Glycerol is a useful byproduct and can be left in the soap
product as softening agent or isolated. The aim of this experiment was to
synthesize soap from vegetable oil and then study its property by comparing it
with commercial soap. The base in hydrolysis determines the texture of the
resulting soap. Solid soap usually consists of sodium salt of fatty acids while
liquid soap potassium salts of fatty acids. In this experiment we used sodium
hydroxide as base for hydrolysis of vegetable oil on the presence of ethyl
alcohol which was used to serve as common solvent for reactant and hence speed
up the reaction. We also studied the properties of soap by comparing the pH of
our soap with that of commercial soap and its ability to form lather and foam
in different solvents such as distilled water, tap water and 1%CaCl.
INTRODUCTION
Soap is produced by hydrolysis of triglyceride (fat or oil).
Triglycerides are esters of fatty acids. Generally soaps are sodium or
potassium salts of long chain fatty acids that are made by hydrolysis of
natural fats such as animal fats or vegetable oil. This base hydrolysis
reaction to make soap is termed as saponification.
The word saponification is the
combination of Latin word “sapo” which means soap and Italian word “sapone”
which also means soap. The production of soap has been around for so long.
People have been producing soap for almost 5000 years. An excavant of ancient
Babylonia revealed evidence that Babylonians were making soap around 2800 BC.
They made soap from animal fat boiled with ashes (which served as lye, NaOH).
Soap was used in cleaning cotton and wool used in textile manufacture and was
used medicinally. (www.soaphistory.net)
In saponification reaction the ester
triglyceride is treated with strong base (Eg. Lye, NaOH) which will accelerate
the cleavage of ester bond and release the fatty acid salt and glycerol. The
fatty acid salt is the soap. When ester react with potassium hydroxide liquid
soap is formed while with sodium hydroxide the solid/bar soap is formed.
General
overall hydrolysis reaction:
fat
+ NaOH ---> glycerol + sodium salt of fatty acid
In this experiment we synthesized
soap using vegetable oil as our starting material. We synthesized solid soap
because we used sodium hydroxide as our base. The experiment also included
determination of properties of synthesized soap and commercial soap through
observing their pHs.
Soap has a cleansing action which is
derived from its polar and non-polar structure with an application of
solubility principle. The long hydrocarbon end is non-polar and hydrophobic
(water repelled) while the salt end is non-polar and ionic and hydrophilic
(water soluble). When greasy oils (non-polar hydrocarbons) are mixed with
soap-water solution, the soap work as a bridge between the polar water
molecules and the non polar oil molecules. The non-polar tail of soap dissolves
into the oil leaving polar carboxylate ions of soap sticking out of oil droplets, making the oil droplets to be suspended in
solution to be washed away by a stream of water. This is called emulsification
and soap acts as a emulsifying agent.
Although soap is excellent cleansers
they also do have a disadvantage. They form insoluble salts when in contact
with water having calcium or magnesium ions. They are precipitated as bathtub
ring when used in hard water because the hard water contains calcium or
magnesium ions which react with soap to form insoluble salts. This insoluble
salts forming bathtub ring leave films that reduce hair luster and gray/roughen
textiles after repeated washings. Synthetic detergents, however may be soluble
in both acidic and alkaline solution and do not form insoluble precipitate with
hard water. This is due to addition of builders and the common used builder is
sodium trimetaphosophate. The phosphate reacts with magnesium or calcium ions
present in hard water and keep them in solution but away from soap
molecules. http://chemistry.about.com/od/cleanerchemistry/a/how-soap-cleans.htm
MATERIALS
AND REAGENTS
·
250 mL Erlenmeyer flask
·
600 mL beaker
·
Ice water bath
·
Glass stirring rod
·
Test tubes
·
Paper towels
·
Commercial towels
·
Boiling water bath
·
Spatula
·
Boiling chips
·
Vegetable oil
·
6M Sodium hydroxide
·
Concentrated Sodium Chloride solution
·
Ethanol (ethyl alcohol)
·
card 1% Calcium chloride
·
Universal indicator
·
Indicator reference
EXPERIMENTAL
PROCEDURES
Part
1:
1. We
placed a 12ml of vegetable oil into a 500ml Erlenmeyer flask, and added 10ml of
ethanol and 12ml of 6M sodium hydroxide to the vegetable oil.
NB: boiling water bath was already prepared for us
and we used freezer as ice water bath.
2. We
continuously stirred the mixture with a glass stirring rod during the heating
process in the boiling water bath to prevent the mixture from foaming up the
sides of the flask.
3. We
heated and stirred for about 30 minutes until the odor of ethyl alcohol was no
longer detected and removed the flask from the boiling water bath.
4. We
placed the flask into the ice water bath and cooled the soap solution for 10
minutes.
5. To
the content of the flask we added 20ml of a concentrated sodium chloride
solution. We carefully decanted the solution to remove the wash solution while
retaining the solid in the flask.
6. We
repeated the washing and decanting step two more times. After the final
washing, we removed the last traces of liquid by dumping the solid unto paper
towels and carefully blotted the soap with addition paper towels.
Part2:
1. We
dissolved a small pea sized piece of our soap in a small test tube containing
5ml of distilled water and heated to help the soap get dissolved completely.
Then we added 2 to 3 drops of universal indicator and observed the color
change. And using the universal reference card we determined the approximate pH
of our soap.
We repeated this experiment using a
purified commercial soap and recorded the observations.
2. In
three separate test tubes placed 5ml each of distilled water, tap water, and 1%
calcium chloride. Added a small pea sized piece of our soap to each separate
test solution and shook vigorously, and recorded the observation on the
relative amounts of lather and foam that appeared in each tube.
3. We
dissolved a small amount of our soap in minimum amount of distilled water, to
the dissolved soap solution we added an equal volume of concentrated sodium
chloride solution and recorded the observation.
RESULTS
TEST
|
pH
|
Observation on leather and foam
formation
|
Observation on addition of conc.
NaCl solution
|
||
Distilled water
|
Tap water
|
1% CaCl
|
|||
Synthesized soap
|
12.5
|
Large amount of leather and foam
were formed
|
Leather and foam formed but did
not exceed that of distilled water
|
Very small amount of leather and
foam were formed
|
The soap particles coagulated and
floated on the surface of solution
|
Commercial soap
|
10.0
|
|
|
The color of our synthetic soap turned to purple on
addition of universal indicator.
DISCUSION
From our
experimental result above the pH of soap was found to be 12.5. From this pH it
shows that our soap is too basic. This is probably the result of excess un
reacted lye (NaOH)
The pH of commercial soap was 10.0 which were relatively
lower compared to our synthesized soap. This is due to the use of controlled
processes in the factory. In the factory the soap is further purified to remove
excess sodium hydroxide. This is done because high pH is not good for the skin
and can cause burns and irritate the skin. The pH for commercial soaps should
at least range from 9.5 to 11.
The synthesized soap showed different
lathering and foam formation on treatment with distilled water, tap water and 1%
CaCl. The lather was much high with distilled water followed with tap water and
very small amount with 1% CaCl. This is because distilled water does not have
impurities of metal cations which will precipitate the salts that’s why the
soap bubbles into full lather. Tap water has some impurities that’s why it does
not as many lather and foam as distilled water does. In 1% CaCl the calcium
ions tend to precipitate the soap forming insoluble salts that’s why it has
almost negligible lather and foams.
In
case of concentrated NaCl, Soaps are sodium salts of fatty acids. Addition of
sodium chloride reduces the solubility of the soap salts. The soaps precipitate
due to a combination of common ion effect and increased ionic strength.CONCLUSION
It is quite clear that soap is important to everyday life, and this can be seen on how long people have been making soaps. That’s why it was of much importance to study the synthesis and the properties of soap so as to increase our knowledge on organic chemistry of soap as well as the risk and importance which can be obtained from using soap.
QUSTIONS
AND ANSWERS:
1. What was the purpose of adding
the concentrated salt solution to your soap preparation?
Answer
The addition of salt causes the
soap to coagulate and float to the surface allowing it to be removed from the
caustic solution.
2. What was the pH of your soap solution? Was
it acidic basic or neutral?Answer
The pH of my soap solution was 12.5 and this is basic soap solution
3. What was the pH of commercial solution? Was it basic, acidic or neutral?
Answer
The pH of commercial soap was 10.0 and it is also basic
4. Describe the observed behavior when your soap was added to each of the following and shaken up:
a) Distilled water
b) Tap water
c) Calcium chloride solution
Answer
a) More lathering, because distilled water has no any
impurities
b)
Less
lathering as compared to distilled water
c) The lather and foam formed was too small and almost
negligible and this is due to reaction of soap with calcium ion to form insoluble
salt
5. What did you observe when concentrated sodium chloride
solution was added to the dissolved soap?
AnswerThe soap particles coagulated forming white precipitates
6. What does the observation in question five suggest about the effectiveness of ordinary soap in sea water.
Answer
Sea and other water which contains appreciated amount of sodium ions interfere with normal behavior of soap because of common ion effect. In the presence of excess sodium ions, the solubility of soap is reduced making the soap less effective.
7. What is the chemical nature of fats and oils, i.e. what class of compound make up the bulk of fats and oils? Are they alcohol, Aldehyde, ketones, acids, esters or amines?
Answer
Vegetable oils and animal fats are triesters of glycerol where the carboxylic acid portion will consist of a range of even numbered carbon chain lengths between C8 and C20 depending on the source of the oil or fat.
General formula; ROOCCH2CH (OOCR) CH2OOCR
Where Rs are odd number alkyl and are either the same or different
8. Describe the chemical reaction that takes place in the processes of saponification. What are the reactants? What are the products? Show a representative chemical reaction for saponification.
Answer
Saponification is the reaction of triglycerides with sodium or potassium hydroxide resulting in formation of glycerol and sodium/potassium salts of carboxylate.
The reactants:
fat and Sodium hydroxide or potassium hydroxide
Products: is glycerol and a crude soap
Representative chemical
reaction is
Answer
Soaps are made of
materials found in nature. Detergents are synthetic (although some of the
ingredients are natural)
Soap form insoluble
salts with hard water forming bathtub ring while detergents does not.
10. Briefly describe how soap or
detergent work to clean your body or to clean other surfaces, such as dishes.
Why these agents (soap or detergent) are needed in order to have thorough
cleaning?
Answer
The cleansing action of soap is determined by
its polar and non-polar structures in conjunction with an application of
solubility principles. The long hydrocarbon chain is of course non-polar and
hydrophobic (repelled by water). The "salt" end of the soap molecule
is ionic and hydrophilic (water soluble).
Detergents and soaps are used for cleaning because
pure water can't remove oily, organic soiling. Soap cleans by acting as an
emulsifier. Basically, soap allows oil and water to mix so that oily grime can
be removed during rinsing
When used for cleaning, soap serves as a surfactant
in conjunction (and also a base) with water.
The cleaning action of this mixture is attributed to the action of micelles,
tiny spheres coated on the outside with polar hydrophilic (water-loving)
groups, encasing a lipophilic (fat-loving) pocket that can surround the grease
REFERENCEwww.soaphistory.net)