Chemical and Physical Properties of Soaps and Detergents

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Discussion of Results and Scientific Explanation

The goal of producing four soaps of different sources and two types of detergents was met in that all soaps and detergents were made properly and able to be used in tests to determine which would be the most eco-friendly and effective choice for an environmental group.

The process of saponification was used to form the different soaps; which is the hydrolysis between an ester and a base to form a soap. Esterification was used to form the detergents, which is the sulphation of glycerol and long-chain fatty acids to form an ester. Other goals included testing the solubility of the soap/detergent starting materials, neutralizing the soap/detergent wastewater through titration, and testing the physical properties of the soaps/detergents.

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The goal to test the pH of well and pond water was met through the use of a pH strip and the goal to test for cations in well and pond water was met through a flame test. The goal to treat the pond/well water to remove contaminants was met through a precipitate reaction as well as the addition of an acid/base to neutralize the water. The goal to test for soap scum was met by observing the soap’s behavior in a beaker of water.

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The goal to test the cleaning abilities of the detergent was met by observing its cleaning of an oily cloth. It can be concluded from these tests that the best choice of soap was the Lard Soap and the best choice of detergent would be Detergent 1; with Detergent 1 being the best overall choice.

The solubility of the starting materials was tested to evaluate the base of the soap’s ability to dissolve in different solutions. It is shown in Figure 2 that vegetable oil was soluble in acetone and toluene, vegetable shortening and lard were partially soluble in acetone and soluble in toluene and olive oil was only soluble in toluene. This is important because if the starting material is insoluble, contaminants will be left in the wastewater of the soap, which is unhealthy for the environment. This makes vegetable oil most desirable because its starting materials will dissolve in more materials than the other soaps and be less likely to leave substances in the wastewater that it is used in.

These solubility results in Figure 2 are consistent with the scientific principles of solubility. Principles state that nonpolar molecules dissolve in nonpolar solvents, which would mean that since oils are nonpolar, they should be soluble in solvents such as toluene and acetone, which are also nonpolar. This is because when the two molecules that are mixed are both nonpolar, the energy of mixing does not favor either side of the reaction; however, entropy favors mixing since this results in more microstates, so entropy drives the reaction and the two molecules mix together. These nonpolar oils should not be soluble, however in polar solvents such as water, hydrochloric acid, or sodium hydroxide- according to accepted scientific principles of solubility. This is due to the fact that since a nonpolar molecule is mixing with a polar molecule, the energy of mixing is positive and favors the reactants, which stops the molecules from mixing. Thus, the results of this test are mostly consistent with scientific principles.

The physical property tests were successful in showing the ability of each soap and detergent to clean, lather, disperse oil in water, as well as their solubility and pH; which were all factors in determining which would be most valuable in the situation of an oil spill. As seen in Figure 3, it is evident that Lard is the best soap because it left no residue and dispersed oil in water. Although the soap had a poor ability to lather, Lard soap was partially soluble in water and cleaned oil exceptionally well, leaving no residue. The pH of the soap was found to be 11; which is similar to many of the other soaps such as olive oil with a pH of 12, vegetable oil with a pH of 11, and vegetable shortening with a pH of 10. While the pH of the Vegetable oil and Lard soaps were the same and they both dispersed oil in water, Vegetable oil left residue in the cleaning test, was insoluble in water, and did not lather well. Vegetable shortening had the most desirable pH out of the soaps because it is closest to neutral. This soap also left no residue and dispersed oil in water; however, it was insoluble in water and did not lather well. Olive oil has the least desirable pH out of the soaps because it is the farthest value from neutral. Olive oil also left residue when cleaning but was partially soluble, lathered well, and dispersed oil in water. The only soap/detergent with a neutral pH was Detergent 1.

Detergent 1 also dispersed oil in water and lathered well. It was partially soluble in water but left little residue when cleaning. Detergent 2 was the worst detergent because although it lathered and was soluble in water, Detergent 2 also left little residue and was the only sample that was unable to disperse oil in water. Its lathered solution also had a pH of 1, meaning this solution was very acidic and would be most harmful to the environment. The ability to lather and disperse oil in water, as well as the amount of residue, are all important factors in choosing the best soap/detergent because it is crucial that they will do a good job of cleaning up the oil from affected wildlife as well as the water in which the oil is in. Soaps and detergents with very high/low pH’s can be harmful, so a neutral pH is ideal for the safety of the environment. If a pH is too low in a body of water, acid rain can occur***. If a pH is too high in the water, it can cause dehydration, irritation of the skin, and even cause some skin diseases to develop in living things (5). Solubility in water is also important because a soap/detergent that is soluble will not leave soap scum in the waters.

Some of the results from the physical properties tests are not consistent with accepted scientific principles. The results showing that the Olive Oil Soap and Vegetable Oil Soap left residue on a watch glass are not consistent with scientific principles that show how the chemical structures of soaps make them good for cleaning. Principals state that soaps have both a hydrophilic end at the carboxylic acid region which is attracted to water and a hydrophobic end which is the chain of fatty acids and attracted to grease. This allows the soap to form micelles, which trap dirt and are then able to be dissolved in water and rinsed away (1). These discrepancies may have occurred because not enough soap was used or not enough scrubbing was put into the watch glass when it was being cleaned.

To determine the source of soap scum, the wastewater of each soap/detergent was tested with a pH sensor to indicate whether the wastewater was acidic or basic. As shown in Figure 1, the soap wastewaters were all basic and the detergent wastewaters were both acidic. This

An acid/base titration then was used to neutralize the soaps/detergents and remove the contaminants. Acid/base titrations are the addition of an acid or a base to a solution in order to neutralize the pH. These are useful in that you are able to record exactly how much of an acid or base is needed to get the pH of a solution to neutral; in the case of this experiment, it was useful in showing which soaps/detergents wastewater would be easiest to neutralize. Each wastewater sample was titrated with either an acid or base depending on the initial pH of the wastewater in order to neutralize the solution (shown in Figure 1). In Figures 4-9, it is shown that Detergent 1 only needed 4.72mL of basic titrant in order to neutralize its wastewater, compared to the 12.55mL that it took to neutralize the wastewater of Detergent 2; this makes Detergent 1 a more desirable detergent because it would be easier to neutralize its wastewater. This table also shows that the Olive Oil Soap needed 0.35mL, Vegetable Oil needed 0.56mL, Vegetable Shortening needed 1.85mL, and Lard needed 2.65mL. This means that Lard is a less desirable soap for an environmental group to use because it shows that it is harder to get rid of contaminants and will more likely be harmful to the environment. Vegetable Shortening would be the second least desirable in this aspect, and then Vegetable Oil. Olive Oil soap would be the most desirable in that it would need the least amount of acid added to its wastewater in order to neutralize it. The four soaps all had basic wastewaters and needed significantly less titrant in order to be neutralized than the detergents. This would make the soaps more desirable because it means that their contaminants would be easier to get rid of. These tests gave insight to the contaminants in the wastewater of each soap/detergent as well as how an environmental group could neutralize them.

One problem that occurred was that the digital stir plate was not used in any of the titrations. This would have impacted the accuracy of the data because the pH sensor may have only been measuring a certain part of the wastewater and not the wastewater as a whole. This makes some of the results from the titration less reliable.

Tests to determine the pH of the well and pond water samples were carried out by placing a pH strip in the water to determine if it was acidic or basic. As seen in Table 4, the pond water was acidic, with a pH of 1 and the well water was also acidic with a pH of 5. Testing for the cations in the pond and well water samples was done through flame tests in which the color of the flame that burned with the water indicated which cations were in the water. In the case of the pond water, the flame burned with no color change, which indicated that the cation present was magnesium (Table 4). The cation that was present in the well water was calcium, as indicated by the red color of the flame (Table 4). Treating the well and pond water to remove contaminants was performed by mixing the waters with known cations in them with a substance that would react with the cation to form a precipitate. The well water was mixed with sodium carbonate to form a calcium carbonate precipitate. The pond water was mixed with magnesium fluoride to form a magnesium fluoride precipitate (3). Each precipitate was then pipetted out of the water to remove the contaminants and the water was then neutralized with the addition of base until a pH strip indicated that the water was neutral.

One issue that occurred was that not all of the precipitate was able to be pipetted out of the water. This may have affected the results of the scum formation test, making them less accurate.

The scum test was done by mixing the Lard soap and Detergent 1 with tap water, well water, treated well water, pond water, and treated pond water. After mixing and letting the mixture sit, it was observed and recorded in Table 5 that scum formed in all the Lard mixtures except for in well water, treated well water, and treated pond water and scum only formed in the Detergent 1 and well water mixture. For the Lard mixtures that formed scum, the results of scum formation are compatible with scientific principles that state that sodium and calcium ions in water react with the soap, forming an insoluble substance in the water, known as soap scum (2). As for the treated well water and treated pond water, there were no contaminants in these water samples since they were neutralized and the cation was removed by way of a precipitation reaction. Since there were no cations to react with the soap, no insoluble substance was form and thus there was no soap scum formation. Looking at the Detergent 1 results, no scum formation in the water is compatible with the scientific principles that show how since detergents have a different ionic group than soaps, the calcium and magnesium ions in the water form a soluble substance with this group and thus there is no scum formation (2). The well water results do not abide by the same principles; this might be because there were other ions in the well water that reacted with the soap to form a soluble substance and reacted with the detergent to form an insoluble substance.

The final cleaning test for Detergent 1 was carried out by putting olive oil on a cloth and scrubbing it with the detergent and water. Detergent 1 was successful in cleaning all of the oil out of the cloth and leaving no residue. These results, as well as all other results, support the conclusion that Detergent 1 would be the best choice for an effective and environmentally friendly cleaning agent.


  1. Chemistry Explained web site, (October 3, 2018)
  2. “Cleaning Chemistry” The Royal Society Chemistry (October 3, 2018)
  3. Cooper M. M., Cooperative Chemistry Laboratories, McGraw-Hill New York, NY, 2015.
  4. Planet Science web site, (October 3, 2018)
  5. Tarun J, Susan J, Suria J, Susan VJ, Criton S. Evaluation of pH of Bathing Soaps and Shampoos for Skin and Hair Care. Indian Journal of Dermatology. 2014;59(5):442-444.

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Chemical and Physical Properties of Soaps and Detergents. (2021, Oct 12). Retrieved from

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