Intro: The purpose of this lab was to analyze commercial aspirin tablets. To do so, the percent acetylsalicyclic acid (active ingredient) in tablets using acid-base titration was determined, the percent acetylsalicyclic acid in tablets by formation of a colored iron(III)-salicylate complex was determined using spectrometry, and then the percents from each process was compared. Acetylsalicylic acid is produced when salicylic acid and acetic anhydride react in the presence of H2SO4. Consequently, the said reaction produces acetylsalicylic acid and acetic acid.
In part one of the lab, titration of a NaOH solution with an indicator and a known concentration into a solution containing a specific amount of Member’s Mark aspirin occurred. Using the balanced equation C9H8O4 + NaOH NaC9H7O4 + H2O, the percent concentration of acetylsalicyclic acid was determined. In part two of the lab, six dilutions of a standard acetylsalicyclic acid were produced and analyzed using a spectrophotometer to determine the maximum absorbance of an iron(III) salicylate complex. Using identical methods, an additional solution was created using Member’s Mark aspirin instead of acetylsalicyclic acid.
The resulting concentration of acid was then calculated using the prepared standard curve (made during the original six dilutions), readings from the spectrophotometer, and Beer’s Law. Results: In part one of the lab, the mass percent of acetylsalicyclic acid within Member’s Mark aspirin was determined through acid-base titration. Table 1. Mass Percent of Acetylsalicylic Acid in Member’s Mark Aspirin | Mass of Tablet| Volume NaOH Delivered| Moles NaOH Delivered| Moles Acid in Tablet| Mass of Acid in Tablet| Mass Percent| Run 1| . 6498g| 23.29mL| . 0018 mols| . 0018 mols| 324mg| 85. 7%| Run 2| .
6507g| 23. 83mL| . 0018 mols| . 0018 mols| 324mg| 85. 3%| Average| | | | | 324mg| 85. 5%| A vital component to the use of spectrophotometer involves the colored iron(III) salicylate complex. Absorbance of each dilution of acetylsalicyclic acid is made possible through this complex. The formation of this complex can be seen by the following balanced equation: Table 2. Various Absorbance of Acetylsalicyclic Acid | Vol. of Standard| Absorbance| Conc. (M)| Blank| 0mL| 0| 0| Std #1| 2. 40mL| .
2393| 2E-4| Std #2| 3. 60mL| . 3877| 3E-4| Std #3| 4. 80mL| . 5048| 4E-4| Std #4| 6. 00mL| . 6177| 5E-4| Std #5| 7. 20mL| . 7386| 6E-4| Std #6| 8. 40mL| . 8782| 7E-4| Logger Pro was used to create a standard curve, Figure 1, which is attached. The curve had a slope of 1246 L/mol and a maximum wavelength absorbance at 528 nm which is shown in Figure 2. This data from the standard curve could then be used in accordance with the spectrophotometer to test for absorbance and to determine the mass percent of acid within the aspirin tablet. Table 3.
Mass Percent of Acetylsalicyclic Acid in Member’s Mark Aspirin | Absorbance| Diluted Conc. (M)| Original Conc. (M)| Moles of Acid| Mass Percent| Sample 1| . 8696| 6. 975E-4| . 01395| . 003488 | 84. 50%| Sample 2| . 8691| 6. 971E-4| . 01394| . 003485| 84. 50%| Sample 3| . 8717| 6. 992E-4| . 01398| . 003495| 83. 89%| Sample 4| . 8630| 6. 992E-4| . 01384| . 003460| 84. 58%| Sample 5| . 8754| 7. 022E-4| . 01404| . 003510| 85. 10%| Sample 6| . 8710| 6. 987E-4| . 01397| . 003493| 84. 70%| Discussion: The results of the aspirin analysis seem to be fairly accurate overall.
Member’s Mark aspirin claims to have 325mg of the active ingredient acetylsalicyclic acid in the tablet, accounting for roughly 86% of the entire pill. In the first part of the experiment, I experimentally found the average mass percent to be 85. 5%. In the second part, the average mass percent was determined to be 84. 55% with a average deviation of . 25%. After examining a wavelength scan, the wavelength that appeared to have the highest absorbance was at 528nm, which can be seen by the graph scan attached. According to Beer’s Law, 528nm would hypothetically give the most accurate results.
Clearly, the two experimental results are both remarkably close to the predicted value. Also, the results show that the Member’s Mark aspirin tablets are within the permissible 5% of the bottle assay. NaOH was not used as the primary standard because of its transparent pigmentation. The spectrophotometer requires a colored solution for optimum accuracy, making the iron(III) a viable candidate since it converts salicyclate ions into a red-purple iron(III) complex. The more accurate method is definitely spectrophotometry.
Titrations are very accurate, but rely on pure observation and a subjective opinion to the definition of the color pink, making definite possibility of error. Spectrophotometry on the other hand uses wavelengths to examine dilutions, a method that is much more accurate than can be possible with the naked eye. Error from this method can only be made during preparation of the dilutions. Even though the first method gave slightly better results, I believe the second method is the clearly superior mode of achieving accurate results.