In this paper will be analyzed two lab reports in the chemical engineering field.  The papers studied the relationship between absorbance and concentration as a function of time. In other words, they studied the amount of light absorbed as a function of wavelength (distance between two points in a wave (Illustrated Glossary of Organic Chemistry – Wavelength, 2022)), and how this absorbance is related with the amount of solute contain in a solution.  The first lab report was focused on showing the linear relationship between concentration and absorbance (which indicates that the higher the absorbance, the higher the concentration) and to illustrate how the concentration varies with time. However, the Second one examines the fact that the molar absorptivity (measure of how well a compound absorbs a given wavelength of light) and the wavelength of maximum absorbance depend on the used substance and change with wavelength. To achieve a great analysis of those paper, the title, abstract, introduction, materials and methods, results, discussion, conclusion, and references of both lab reports were studied and compared separately.

Title

The first lab report was titled “Determining the relationship between absorbance and concentration as functions of time, via component balance reactor.  The title is really detailed and really reflect what is the main topic of the experiment. The second lab report title is “UV-VIS Molecular Absorption Spectroscopy Determination of Molar Absorption and Wavelength of Maximum Absorbance.” As the first one, this title is also very informative, helping the reader to know their interest for the report easily. By seeing, only, the titles of both lab reports, people can find out what they want to test with this experiment and what methods and machinery will be used. 

Abstract

The abstract is the section that summarize the entire lab report. In the abstract section, the first lab report states the overriding objectives and materials used during the experiment. It says that the experiment was focused to define the molar absorptivity of a red and green dye solution which names are Fast green FCF (FD &Green3) and Allura red AC (FD& Red 40), and to obtain the linear relationship of absorbance and concentration at 512 and 627 n. It also indicates that the concentration change with time will be analyzed using a continuous stir tank reactor (CSTR), giving a brief explanation of the methods and material. However, it does not show enough information about the final finding of the experiment. Moreover, the abstract was written in a clear and organized way, making it easy to see the main structure of the entire experiment.

The abstract of the second lab report shows as its goal the calculation of the maximum absorptivity of different concentration of an organic compound name Potassium manganate to build a calibration curve (graphic representation) when the relationship of concentration and absorptivity can be observed. The author of the second lab report summarizes nicely the objectives, methodologies, and materials, but it is also missing information of the specific final finding of the experiment. The language used during the report was clear enough, except for the use of chemical nomenclature such as KMnO4 0.002 M without explaining that KMnO4 is the name of the compound and 0.002 M the amount of it contained in a mixture, making the paper less understandable for the reader.

Introduction

The introduction of the first lab report shows basic information to help the reader understand and connect with the context of the experiment. The author explains the Beer-Lambert law, since this law support the objective of this experiment. In the introduction of the report was detailed the Beer’s Lambert law. That law states that the absorbance and the concentration of a substance are directly proportional. That means that when the concentration increases, the solution will absorb more light and when the concentration decreases, the solution will absorb less light.  The author also introduces equations that play a really key role in the base theory of the experiment, and it was numbered so that it could be reference later. It was introduced equation such as A = E l C, but each of the variable contained in the formula were not defined. Furthermore, in the introduction it was also explained how it will determine the absorbance of a compound with known absorptivity and changing concentration using a differential equation, summarizing thus a little part of the methodology.

The introduction of the second lab report as the first includes enough background information to describe the hypothesis of the experiment.  During the introduction, this author provided definitions to many theoretical terms to reinforce the clearness of the report. It was defined that spectroscopy is based on studying the interaction of light with matter. In addition, were added information of terms and law that support the experiment such as absorptivity and the Beer-Lambert law as well. The author also included information on the calibration curve. He teaches that the calibration curve is going to be obtained experimentally, using some known concentration solution. The absorbance of these solutions will be measured for a certain period of wavelength and later, allowing him to build the curve by placing the obtained data in programs as Matlab. By adding a little description of the methods used to build the curve, help to persuade the readers that the methods implemented during the experiment were appropriate.

Materials and Methods

In the first lab report, the materials used in the experiment were not list out, but were specified during the description of the methodology. It was certified that materials as green dye, red dye, a pump and a CSTR or Continuously Stir Tank Reactor were used during the experiment performance.  All the follow steps were described in order in this section. But the author did not include enough details of the procedure. The author states that the first step done in the experiment was the dilution of the red and green dye, but it was not detailed which substance was used to dilute the dyes and what amount was used to dilute them.  He also shows how he analyze their data by discussing that to find the molar absorptivity the data for concentration and absorbance collected during the experiment were plotted and the slope of the graph helped to find the molar absorptivity.

In this section of the second lab report, the materials used were listed in a table and a brief description of how the equipment was installed was also provided. The author indicates that 10 ml pipettes, caffeine solution, an analytical balance and a UV-Vis Spectrophotometer were used in the process. The method was described, but not enough detail was provided for others to perform the same experiment. The author also did not explain how the data obtained in the experiment was analyzed.

Results

In the lab report 1, the author preferred to place the results and discussion in the same section. All the data collected during the experiment were not presented, if not that some graphs that show their finding are shown and analyzed. Through the graphs and explanations, the author shows that the relationship between absorbance and concentration is a linear one, confirming the Beer-Lambert law.

The author of the lab report used this section to show all the data collected during the experiment. The data were presented organized in tables. Furthermore, the graphs obtained through analyze the raw data, were provided, including text below the graphs to explain their significance. Plots such as absorbance versus wavelength, and a calibration curve of concentration versus absorbance were presented in this section. 

Discussion

The first lab report does not have a discussion section, while the second did. In that section, the author of the second lab report discusses and explains the findings of the experiment, and shows whether they verify the hypothesis outlined in the introduction. It was verified that the wavelength maxima do not depend on the concentration of the substance. In the discussion it was also stated that the calibration curve reproduces the Beer-Lambert law since the graph shows an increasing line in which concentration and absorbance proportionally.

Conclusion

The first lab report does not have the conclusion in a separate section, but rather concludes in the section named results and discussion. The author basically used his findings as the conclusion of the experiment. However, in the second lab report, the author summarizes the main finding of the experiment that agrees with the Beer-Lambert law and the rest of the theory discussed in the introduction, in order to persuade readers that the experiment was carried out well. The author ended the lab report by saying that the experiment was successful, as the molar absorptivity and maximum wavelength were calculated. Furthermore, the calibration curve was achieved using the data from the experiment.

References

Both the first and the second lab report have all the information used in the report cited. The first lab report cited just one source, while the second one cited more than one sources organized in an alphabetical way.

Conclusion

Each of the lab reports are well written. The objectives of each lab report were clearly described, using descriptive and precise language. Although the first lab report provides more details when describing the objectives and steps carried out during the experiment, the second lab report presented a very broad and concise theoretical framework, allowing the reader to understand each scientific term used in the lab. report. Both authors provided graphs and numerical data, thus helping to increase the credibility of these experiments. Both the author of the first lab report and the second showed that the experiments carried out were successful, since they were able to demonstrate the linear relationship between concentration and absorbance.

References

 Gaba, A. (2018, November 9). Determining the Relationship between Absorbance and Concentration as a Function of Time, Via Component Balance Reactor. ChE228_Lab_Report_2_Gaba_Anjali.pdf – Fall 2018 ChE 228 November 9th, 2018 Laboratory Report 2 Determining the relationship between absorbance and | Course Hero. Retrieved April 14, 2022, from https://www.coursehero.com/file/65379482/ChE228-Lab-Report-2-Gaba-Anjalipdf/

Illustrated glossary of organic chemistry – wavelength ( λ ). (n.d.). Retrieved April 14, 2022, from https://www.chem.ucla.edu/~harding/IGOC/W/wavelength.html#:~:text=Illustrated%20Glossary%20of%20Organic%20Chemistry%20Wavelength%20%28%CE%BB%29%3A%20In,cycle.%20This%20can%20be%20crest-to-crest%2C%20trough-to-trough%2C%20null-to-null%2C%20etc.

UV-vis molecular absorption spectroscopy determination of molar absorptivity Y. StuDocu. (n.d.). Retrieved April 2022, from https://www.studocu.com/pe/document/universidad-nacional-agraria-la-molina/quimica-analitica/informe-9-espectroscopia-de-absorcion-molecular-uv-vis-determinacion-de-absortividad-molar-y-longitud-de-onda-de-maxima-absorbancia/11210817