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?

Answer
The 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

9. How does soap differ from detergents?
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

REFERENCE
www.soaphistory.net)

http://chemistry.about.com/od/cleanerchemistry/a/how-soap-cleans.htm