1. Aim To determine the percentage of aspirin in different commercial preparations and to find which is the best value for money 2. Hypothesis The greater the percentage of acetylsalicylic acid (ASA) in the tablet, more powerful and efficient the aspirin would be due to the way aspirin works in human’s body. Aspirin is often used to alleviate the pain, and the sensation of pain is mainly attributed to a chemical substance called prostaglandins, which is responsible to send a strong signal to the brain to remind the damage of the body.
Working cells in the damaged area produce prostaglandins using an enzyme called cyclooxygenase 2 (COX-2), and aspirin works by disturbing COX-2 functions. By doing so prostaglandins are no more produced, and the pain is revealed while the body damage still exists. Therefore it indicates that the more amount of acetylsalicylic acid (ASA) being taken, the more COX-2 enzymes become unavailable of producing prostaglandins and the weaker the signals are sent to the brain, which result in less pain.
For this reason, it is very likely to be the percentage of acetylsalicylic acid (ASA) affecting the efficiency of aspirin, and this could be proved through simple neutralization reaction by titration with basic solution, such as sodium hydroxide. The more sodium hydroxide needed in the titration, the more the amount of ASA in aspirin, thus the more powerful the aspirin is. The equation would be: C6H5OCOCH3COOH+NaOH > C6H5OCOCH3COONa++ H2O As the percentage purity of the aspirin is calculated, the value should be compared to its price per gram.
The table below shows three different brands and their price. Brand| Package (g)| Price (RMB)| Bamyl| 10 tablets ? 0. 5g| 6| Bayer| 30 tablets ? 0. 1g| 20| Baijunyu| 100 tablets ? 0. 025g| 20| The table below shows the price for each brand per gram, to compare with the percentage purity after the experiment. Brand| Price per gram (RMB/g)| Bamyl| 6? 10 ? 0. 5 = 1. 2 RMB/g| Bayer| 20? 30 ? 0. 1 = 6. 67 RMB/g| Baijunyu| 20? 100 ? 0. 025 = 8 RMB/g| 3. Variables | |.
Independent Variable| The brand of aspirin (the percentage purity of ASA in aspirin)| Dependent Variable| The efficiency of aspirin (the amount of sodium hydroxide used to titrate ASA in the aspirin)| Constant Variable| Mass of aspirin being used, concentration of the alcohol used to dissolve aspirin, concentration of sodium hydroxide, drops of phenolphthalein| 4. Equipments & Apparatus Different brands of aspirin (at least 3) 50cm3conical flask ±0. 5ml (? 1) 50cm3beaker ±5ml (? 1) Electric balance g ±0. 001g (? 1) .
Phenolphthalein 0. 100 mol dm-3sodium hydroxide Grinding equipment (1) 5. Procedure 1. Note the brand name and the price of the aspirin tablets. 2. Prepare all the equipments needed in the lab. 3. Grind the aspirin tablet into powder. 4. Weigh out accurately 0. 4g of aspirin using an electric balance. 5. Put the powder into a 50cm3conical flask and dissolve it in 10cm3of 95% alcohol. 6. Stir the solution evenly to ensure that all the powder has been dissolved in alcohol. 7. Titrate the solution with 0. 100 mol dm-3sodium hydroxide solution using two drops of phenolphthalein as an indicator. Record the amount of sodium hydroxide being used to neutralize the acid.
8. Repeat the above procedures with different brands of aspirin. 9. Calculate the percentage of ASA in each brand 10. Compare the percentage of ASA in each brand of aspirin with the price of the aspirin per gram and conclude the most cost-efficient aspirin among those brands. 6. Data Result Uncertainty of the equipment Burette ±0. 05cm3 Measuring cylinder ±0. 5cm3 Electric Balance ±0. 001g Total percentage uncertainty = (0. 0523. 13? 100+0. 510? 100+0. 0010. 5? 100) = 5. 4% Table | Trial 1| Trial 2| Trial 3| Initial volume(cm3)| 0| 0| 0| Final volume(cm3)| 22. 40| 22. 00| 25. 00|
Actual volume(cm3)| 22. 40| 22. 00| 25. 00| Average(cm3)| 23. 13| Calculation of the percentage purity C6H5OCOCH3COOH+NaOH > C6H5OCOCH3COONa++ H2O No. moles of NaOH = 0. 1 mol dm-3 ? 23. 13 cm3 ? 1 dm3 = 0. 002313 No. moles of C6H5OCOCH3COOH = No. moles of NaOH = 1 mole Mass of C6H5OCOCH3COOH = No. moles of C6H5OCOCH3COOH ? Molecular mass of C6H5OCOCH3COOH Molecular mass of C6H5OCOCH3COOH=(12? 9+16? 4+1? 9) = 181 Mass of C6H5OCOCH3COOH = 0. 002313 ? 181 = 0. 418653g Percentage Purity of C6H5OCOCH3COOH in aspirin tablets = 0. 4186530. 5? 100=83. 7306% Percentage Uncertainty = 83. 7% ± 5. 4%.
Actual Percentage Purity of C6H5OCOCH3COOH in aspirin tablets = 99. 5 % Percentage Error = 99. 5-83. 730699. 5? 100 = 15. 84% Percentage purity of other aspirin brands Brand| Price(RMB)| Package (g)| Percentage Purity (%)| Bamyl| 6| 10 tablets ? 0. 5g| 80. 36(Sisi)| | | | 79. 24 (Erica)| | | | 83. 7 (Martin)| | | | 81. 1 (Average)| Bayer| 20| 30 tablets ? 0. 1g| 89. 1 (Rimi)| | | | 89. 2 (Linda)| | | | 89. 15 (Average)| Baijunyu| 20| 100 tablets ? 0. 025g| 50 (Selena, Average)| Percentage uncertainty and percentage error of other aspirin brands Brand| Percentage Error| Percentage uncertainty|.
Bamyl| 99. 5-81. 199. 5? 100 = 18. 49%| 81. 1% ± 5. 4%| Bayer| 99. 5-89. 1599. 5? 100 = 10. 40%| 89. 2% ± 5. 4%| Baijunyu| 99. 5-5099. 5? 100 = 49. 74%| 50% ± 5. 4%| Note: In the calculation of percentage uncertainty and percentage purity, average values were taken to minimize the error. 7. Data Analysis & Evaluation Regardless of the possible errors in the experiment, each three brand showed obvious difference in their percentage purity of ASA. Bayer had the highest percentage purity of 89. 2%, which is also the closest to the actual percentage purity, and moreover the data was precise(89. 1% and 89.
2%). However, the percentage error (18. 49%) is way greater than the percentage uncertainty (5. 4%), and the value does not fall within the range 99. 5% ± 5. 4%. Since random error is estimated by the uncertainty and it is smaller than the percentage error, systematic errors are at work making the measured data inaccurate. The similar results were noted for two other brands, Bamyl and Baijunyu, and especially Baijunyu showed the highest percentage error of all (49. 74%), which makes it highly doubtful about its accuracy in the experiment. All three brands weren’t able to fall within the range 99.
5% ± 5. 4%, and as the percentage error for all three brands is greater than its percentage uncertainty, it is considered that systematic error is the biggest reason for inaccuracy in the experiment. However, in spite of the failure in calculating accurate percentage purity that falls in the region 99. 5% ± 5. 4%, it was accurate enough to find out the most cost-efficient brand among three. The table below shows the comparison between the price of aspirin per gram and the percentage purity. Brand| Price per gram (RMB/g)| Percentage purity (%)| Bayer| 6. 67| 89. 2| Bamyl| 1.
2| 81. 1| Baijunyu| 8| 50| As shown in the table, the prices correspond to its percentage purity, in other words, efficiency. The higher the price, the more effective the aspirin is. In this point, as the experiment was able to achieve a reasonable comparison between the price and the percentage purity of three different aspirin brands, it can be considered as a success. In order to find out the most cost-efficient brand, it is necessary to compare the price and the percentage purity. In price, Baijunyu has the highest price (8 RMB/g) compared to other two products (1.2RMB/g & 6. 67 RMB/g).
Its price is approximately 6. 67 times more expensive than Bamyl, and 1. 2 times more expensive than Baijunyu. In percentage purity, Baijunyu has the least percentage purity of all (50%), while the percentage purity between Bayer and Bamyl is similar (89. 2% & 81. 1%). Bayer is 1. 09 times more efficient than Bamyl, and 1. 78 times better than Baijunyu. Comparing the difference in price and percentage purity between three brands, Bamyl is considered to be the most cost-efficient brand with relatively high efficiency in its function.
Bamyl is 6 times cheaper than Bayer, but it is only 9% less effective than Bayer. For this reason, Bamyl is the most cost-efficient brand among all three brands. As the experiment was able to find out the percentage purity of aspirin in a brand and also the most cost-effective one from 3 different brands, the experiment is successful. However, since there was a significant difference in percentage error and percentage uncertainty, it is necessary to evaluate the possible errors for future improvements.
As analyzed, the systematic errors are at work in making the measurements inaccurate. There are several reasons that cause the systematic errors: Miscalibration of a measuring device. Measuring the volume of water from the top of the meniscus rather than the bottom Overshooting the volume of a liquid delivered in a titration Poor insulation in calorimetry experiments Except for the last one, all other three reasons can directly affect the accuracy in this experiment. The electric balance might cause miscalibration in measuring the mass of aspirin tablets.
Students might have forgot to reset the value to zero before put the aspirin tablet on the filter paper, or the electric balance itself has problems. Actually, students had to change an electric balance because it was likely that the electric balance was not working properly. In order to avoid this, students have to make sure that there is no problem in any equipment, and the value is zero before the measurement. The mistakes in measuring the meniscus happen all the time, and the only way to prevent the errors in reading the meniscus is to take additional care.
The students have to be aware of the correct way of reading the value; Measure the meniscus at eye level and read to bottom of the meniscus in most liquids and the top of the meniscus if it is mercury. In most liquids, include water, the meniscus is concave, but in mercury, it is convex. Therefore there is a difference in reading the values of meniscus, and students should know. A: Concave B: Convex The last one, overshooting the volume of liquid during the titration, is inevitable. However it could be minimized.
Students have to shake the conical flask constantly, because the color change in one region does not mean complete neutralization. Only after the whole part of the volume changes its color, neutralization is completed. Furthermore the students have to have a standard color, in other words, standard depth of the color, in order to avoid the overshooting, because the deeper the color, the more basic the volume becomes. And since this kind of error is inevitable, students should try their best to minimize the errors by shaking the flask and be aware of the depth of the color. 8. Conclusion.
There were a lot of mistakes in this experiment, mostly systematic errors, as the percentage error is greater than percentage uncertainty. However, evaluation has been done and it is sure that there will be improvements in future experiment. Moreover, in overall, the aim of this experiment, to determine the percentage of aspirin in different commercial preparations and to find which the best value is for money, was achieved quite successfully through the comparison between the price of the aspirin brand per gram and its percentage purity of ASA. Therefore, it could be concluded, that this experiment is a success.