To determine the percentage of aspirin in different commercial preparations and to find which is the best value for money
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.
| Package (g)
| Price (RMB)
| 10 tablets × 0.5g
| 30 tablets × 0.1g
| 100 tablets × 0.025g
The table below shows the price for each brand per gram, to compare with the percentage purity after the experiment.
| Price per gram (RMB/g)
| 6÷10 × 0.5 = 1.2 RMB/g
| 20÷30 × 0.1 = 6.67 RMB/g
| 20÷100 × 0.025 = 8 RMB/g
| 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)
* 0.100 mol dm-3sodium hydroxide
* Grinding equipment (×1)
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%
| Trial 1
| Trial 2
| Trial 3
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