Introduction
The study of pH is an important task in industrial, clinical, and laboratory clinics because the results of the measurement are used to investigate the potential applications of samples. Strictly speaking, pH is a measure of the acidity of the medium and the more protons present in the solution, the lower the pH (EPA, 2023). The overall objective of the present work was divided into two successive tasks: the study of pH by two different methods for eight different substances, and the synthesis of soap with further determination of the acidity of the product.
Methods
The present laboratory work was based on experimental design. Eight samples shown in Table 1 were given in advance for the work. Using universal indicator paper and a pH meter, the acidity values (estimated and exact) for each sample were measured, and the results were recorded in Table 1. A soap solution was prepared separately: for this, 0.8449 g of sodium hydroxide was dissolved in 5 mL of distilled water and then in 5 mL of 95% ethyl alcohol. An additional 50-mL Erlenmeyer flask was filled with 1.260 g of lard (natural fat). The entire volume of the previously prepared sodium hydroxide was added to the fat, and the mixture was then heated to boiling until a precipitate formed. Once the precipitate began to form, the heated mixture was removed from the stove and repositioned to cool.
Additionally, the reagent was prepared by transferring 20 mL of concentrated sodium chloride solution into a 100-mL beaker. The sample from the Erlenmeyer flask prepared earlier (see previous paragraph) was added to the solution, and the mixture was then placed in an ice bath. The mixture was subjected to filtration on a Buechner funnel and was also washed with distilled water to remove excess reagents. A small portion of the sample after filtration was used to measure pH.
Data and Results
Table 1 shows the direct pH measurements — using indicator paper and pH meter — for the eight samples studied. As can be seen from the results, Lime juice, Vinegar, Diet Pepsi were the most acidic, Apple juice and Sparkling water were moderately acidic, Tap water, which should have been neutral, was slightly acidic due to impurities in the composition, Milk/creamer was slightly basic, and Liquid soap was the most basic of the whole sample of samples. It is also evident from Table 1 that there were differences between the measured results using the paper and pH meter.
For samples with higher acidity, the pH meter always showed a higher result than the paper indication, whereas for substances of weak acidity or neutral, the pH meter estimated lower results. It can also be seen that for Liquid soap, no difference was observed between the determined pH values from the two methods. An exciting result also concerned the significant differences between the values of the two measurements. Specifically, for Sparkling water and Tap water, the paper indication indicated a neutral environment, whereas the pH meter showed a weak acidity. On the contrary, for Milk/creamer, the pH meter identified the medium as slightly essential, while the paper indication indicated a neutral medium.
Table 1: Results of estimated and accurate pH measurements for eight samples.
The table shows the pH data measured by the two methods as well as the results of the visual examination.
In the main part of the experiment, the pH of the sample remaining after filtration was measured by paper indication and recorded in Table 2. The estimated pH value was found to be 12, indicating a strongly basic (alkaline) sample environment. State the experimental yield and the percent yield of the soap product.
Table 2: Results of direct measurement of sample (soap) pH and calculations.
The detailed calculations for the two values in the table are shown below:
To calculate the theoretical product yield, the balanced equation must first be constructed (Helmenstine, 2020):
TG + 3NAOH → C3H8O3 + 3 • soap
Based on the data, the theoretical mass of the soap obtained:
The empirically determined mass of the product was 8.0532 g, which gives a critically excessive value for the percent yield:
% yield = 8.0532 / 1.2303 × 100% = 654.6%
Discussion
The present experimental work was devoted to studying the pH of different samples and the synthesis of soap based on sodium hydroxide, with further determination of pH. The results showed that the pH of the eight samples differed depending on the use of paper indication or pH meter. The main reason for this discrepancy leading to inconsistent results is the inaccuracy of the paper indication method, as it only gives approximate values. In addition, differences in color shades can be difficult to perceive, introducing subjectivity into the results. In contrast, the pH meter, which measures the concentration of protons in a sample, gives more accurate results and is not related to color perception mechanisms.
The study also showed that the synthesized soap belongs to alkaline products, as the corresponding pH was 12. This correlates perfectly with the results as the soap is made from a mixture of fat and hydroxides and is a salt of fatty acids (Jabr, 2020). Despite the presence of acid anions in the dissociated salt solution, they are weak due to their organic nature, which is fully compensated by the strength of the hydroxide groups present. The results of calculations showed that the percentage yield of the product was equal to almost 655%, which is critically high and unacceptable for the tasks of analytical chemistry. Among the potential reasons for this outcome is the presence of solid impurities in the composition of the precipitate, which increased the mass of the alleged soap.
Conclusion
The present study was focused on the study of pH by two methods (paper indication and pH meter) for eight samples and synthesized soap. The results showed that the pH meter provides more accurate values of the medium’s acidity, while the paper indication may lead to erroneous results due to approximation and color perception patterns. The high product yield because of the work showed low identification accuracy, indicating the potential for impurities and incomplete dissolution of lard.
References
EPA. (2023). pH. US Environmental Protection Agency. Web.
Helmenstine, A. M. (2020). How saponification makes soap. ThoughtCo. Web.
Jabr, F. (2020). Why soap works. YSM. Web.