Syntheses of Soap and Detergent

November 20, 2017 | Author: Chin Castro Zabat | Category: Soap, Sodium Hydroxide, Sodium Chloride, Solubility, Molecules
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SYNTHESES OF SOAP AND DETERGENT Cia Cirelle Panol, Lyka Mariz Reyes, Benedict Priela, Madeleine Robles, Jonathan Bryan Rosales, Arianne Joy Salas Group 8 2A Medical Technology Organic Chemistry Laboratory

ABSTRACT Soaps could be prepared by a process called saponification; it involves reactions of fats by adding alkali to the mix at the end to form soap and two byproducts, water and glycerol. This experiment used fats or oil, sodium hydroxide, saturated sodium chloride solution and water to synthesize soap. Preparation of detergent was also conducted, a sodium alkyl sulfate called sodium dodecyl sulfate was prepared by a reaction of dodecanol with sulfuric acid. The resulting dodecylsulfate was converted to sodium salt by neutralization with sodium hydroxide. Test for glycerol and the comparison of the soap and detergent in hard water was also observed and tested in the experiment.

INTRODUCTION: A soap is the sodium or potassium salt of a long chain fatty acid. [1] The fatty acid usually contains 12 to 18 carbon atoms. Solid soaps usually consist of sodium salts of fatty acids whereas liquid soaps usually are potassium salts of fatty acids. Soap consists of a polar end and a non-polar end. Soaps are called amphipathic molecule due to this dual nature. [2]

the center of the micelle. This is how soap cleans technically. When rinsed with water, the micelle together with the dirt washed away. Soap is theoretically acting as an emulsifying agent, where emulsion is the dispersion of a liquid in a second immiscible liquid. [3]

Figure 2. A micelle (photo source:

Figure 1. Condensed Structural and Skeletal Formula of soap (photo source: A micelle, a spherical shape is formed resulting from the negatively charged heads of the soap molecules. They then orient themselves, where the non-polar tails rearrange towards the center of the micelle and the hydrophilic site facing the water. In the presence of oil or dirt, the nonpolar head interact with them, and gathered it to

Treatment of fats or oils with strong bases such as lye (NaOH) or potash (KOH) causes them to undergo hydrolysis (saponification) to form glycerol and the salt of a long-chain fatty acid (soap). [4] Because soaps are the salts of strong bases and weak acids they should be slightly basic. If a soap is too basic it could cause damage to skin, surfaces to be cleaned, or clothes. Since the cleansing action of soaps depends upon the fact that they ionize readily in water, you can imagine what would happen if the ionic end lost its charge. The soap would no longer be attracted to

water molecules and could no longer emulsify oil and dirt. This is just what happens in hard or acidic water. Hard water contains metal cations, such as Ca2+ and Mg2+, that react with the charged ends of the soaps to form insoluble salts. The insoluble salts that Ca2+ and Mg2+ form with soap anions cause the gray precipitate commonly called bathtub ring.

Test for complete saponification was done by adding a drop of mixture to 1 mL of water, when no trace of oil was observed, saponification was completed. The mixture was stirred until it became homogenous. This mixture was poured in hot solution with vigorous stirring into 50 mL of cold, saturated NaCl solution. This mixture was used to test for glycerol and its behavior in hard water. 2. Extraction and Test for Glycerol

Figure 3. Expanded Formula of Detergent (photo source: Synthetic detergents were developed to overcome these limitations of soaps. Detergents are similar to soaps in having an ionic end and a nonpolar end. They have different structures, however, which make them less susceptible to forming insoluble Ca2+ and Mg2+ salts. [5]

EXPERIMENTAL A. Compounds tested (or Samples used) 20% of NaOH, 6M NaOH, concentrated H2SO4, 1% CaCl2, 1% MgCl2, saturated NaCl solution, phenolphthalein, dodecanol (C12H25OH), ice, oil, water, 95% ethanol B. Procedure 1. Preparation of Soap Soaps are prepared by saponification. 30 mL of 6M NaOH was mixed with 50 mL of water. In a 500 mL beaker, the mixture was heated and stirred frequently. 15 mL of oil was added in portions into the mixture. It was heated for 15-20 minutes with frequent stirring to replace the water lost by evaporation.

The mixture from the preparation of soap was diluted with HCl, it was evaporated to a small volume or to a syrupy consistency. It was allowed to cool. The residue was added with 10 mL of 95% ethanol. The alcoholic extract was then evaporated in a water bath. The residue contains the glycerol. The test for glycerol was done by adding a pinch amount of powdered potassium bisulfate, it was heated strongly and the odor was observed and recorded. 3. Preparation of Detergent Preparation of detergent was prepared by reacting 5 mL of dodecanol in a 100 mL beaker with 2 mL of concentrated H2SO4. The solution was continually stirred for 1 minute after the slow addition of the acid. The mixture was then left to stand for 10 minutes. In a beaker, 5 mL of 6M NaOH was mixed with 10 mL of water. It was mixed well and then added with 4 drops of phenolphthalein. The pink color of the phenolphthalein began to fade due to the presence of strong basic solution. After 10 minutes, the NaOH solution was poured into the dodecanol-sulfuric acid mixture. It was stirred until the pink color disappears. A large amount of solid detergent was formed.

A 250-mL beaker was filled with one-third full of ice, this was added with 50mL of NaCl and mixed thoroughly. Water was added to bring the total volume up to 75 mL. The detergent mixture was poured into the icesalt bath and stirred to break the large lumps of the detergent.

Soaps prepared by saponification which is the alkaline hydrolysis of fats and oils. A by-product of this reaction is glycerol.

This mixture was used to test its behavior in hard water. 4. Behavior in hard water With two test tubes per soap and detergent solution, each was filled with 5 mL. The first test tube was added with 2 mL of 1% CaCl2 and process was repeated for the second test tube but was instead added with 1% MgCl2 solution. The content was mixed and formation of precipitate and how much (very large, large, little, none) was noted and recorded. Test for the emulsifying ability was done by adding 1 drop of cooking oil in to each tube; it was stopped and mixed vigorously. The amount of suds formed and how much was noted and recorded.

RESULTS AND DISCUSSION 1. Properties of Soap and Detergent The preparation of soap underwent this chemical reaction:

Figure 5. Preparation of Detergent (photo source: Organic sulfonic acid and phosphoric acid salts, commonly known as detergents are prepared by the reaction of dodecanol in NaOH and H2SO4. In this experiment the properties of soaps and detergents were compared.

Color and appearance Solubility in 1% CaCl2 Solubility in 1% MgCl2 Emulsifying ability

Soap White solidified gelatin Insoluble

Detergent White amorphous precipitate Clear solution


Clear solution

Light suds

Heavy suds

Table 1. Properties of Soap and Detergent The table above shows the different properties of soap and detergent. As recorded above, the color and appearance of soap, was white solidified gelatin while that of detergent was white amorphous precipitate. In the test of behavior in hard water, the soap’s and detergent’s solubility in 1% CaCl2 and 1% MgCl2 showed the following results. Soap is insoluble to both 1% CaCl2 and 1% MgCl2. This is because the soap forms precipitate with calcium or magnesium ion as shown below:

Figure 4. Preparation of Soap (photo source:

CH3(CH2)14COO-Na+ + H+ → CH3(CH2)14COOH + Na+ In hard water (water with a high concentration of mostly magnesium and calcium) these ions react with the carboxyl end forming insoluble salts (commonly called “bathtub ring” or “scum”).

CH3(CH2)14COO-Na+ + Ca2+ → (CH3(CH2)14COO-)2Ca (insoluble) Once those salts precipitate the soap cannot clean. On the other hand, this property was overcome by the detergent. Detergent tested with its solubility in 1% CaCl2 and 1% MgCl2 showed that the synthesized detergent was soluble to both ions. From the experiment, detergent was found to be much more effective cleaning agents because they do not readily form insoluble complexes with the ions in hard water. The emulsifying ability of both soap and detergent was also tested. Soap produced light suds while that of detergent produced more and heavier suds. The cleaning action of both soaps and detergents results from their ability to emulsify or disperse water-insoluble materials (dirt, oil, grease, etc.) and hold them in suspension in water. 2. Observation from the test of Glycerol The residue containing the glycerol is heated with potassium bisulfate, and acrolein is released. When a fat is heated strongly in the presence of a dehydrating agent such as potassium bisulfate (KHSO4), the glycerol portion of the molecule is dehydrated to form the unsaturated aldehyde, acrolein (CH2=CH–CHO), which has the odor peculiar to burnt cooking grease.


[1] Bayquen V. A., Cruz C.T., de Guia R. M., Lampa F. F., Pena G.T., Sarile A.S., Torres P.C. (2009) Laboratory Manual in Organic Chemistry. EDSA, South Triangle, Quezon City, Philippines: C&E publishing Inc. [2] /general/lab10.html 09/29/12 [3] Chemistry_bak/Chem162/Chem162labs/Exp4_So ap_and_detergents.pdf 09/29/12 [4] soaplab.htm 09/29/12 [5] labs/LABS12.html 09/29/12 [6] %20detergent.pdf [7] /physicalscience/soap.pdf [8] [9] /che4x/e6sapon.pdf [10]

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