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Analysis of Aspirin tablets

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Laboratory report 7 - Analysis of Aspirin Tablets Name: Leung Dik Ka (14) Name of partner: Lee Wai Chi Date: 19/11/2008 Title of the experiment: Analysis of Aspirin Tablets Aims: To analyze the amount of the active ingredient in different commercial brands of aspirin tablets is carried out, to see whether the manufacturers' claims are justified. Introduction Pharmaceutical manufacturers are required by law to state on the packaging the amount of each active ingredient in their products. In this experiment a consumer survey on the amount of the active ingredient (2-ethanoyloxybenzoic acid, or o-acetylsalicylic acid) in different commercial brands of aspirin tablets is carried out, to see whether the manufacturers' claims are justified. 2-ethanoyloxybenzoic acid can readily hydrolyzed, using a known excess of sodium hydroxide, into the sodium salts of two weak acids, ethanoic acid and 2-hydroxybenzoic acid. The excess amount of sodium hydroxide is then estimated by a back titration with standard sulphuric(VI) acid. The equation for the hydrolysis reaction is: CH3CO2C6H4CO2H + 2NaOH(aq) --> CH3CO2Na (aq) + HOC6H4CO2Na (aq) + H2O (l) Phenol red (pH range 6.8-8.4) is most suitable for this titration due to the presence of the salts of two weak acids, though phenolphthalein is also satisfactory for the present purpose. ...read more.


used in hydrolysis of 2-ethanoloxybenzoinc acid =1 x 0.025 - 1.44864 x 10-3 x 10 =0.0105136mol No. of mole of 2-ethanoloxybenzoinc acid in the weighed sample =0.0105136/2 =0.0052568 mol Mass of 2-ethanoloxybenzoinc acid in 3 Aspirin Tablets =0.0052568 x 180 =0.946224g Mass of 2-ethanoloxybenzoinc acid in 1 Aspirin Tablet = 0.946224/3 = 0.315408g Price of 1 tablet = 30/100 = 0.3$ Price per g of 2-ethanoloxybenzoinc acid = 0.3/0.315408 = 0.951$/g Discussion In the hydrolysis of the aspirin, the 25cm3 of distilled water added was not necessarily be accurate, because the number of moles of aspirin and sodium hydroxide was still the same in the conical flask no matter how much distilled water was added to it. Also, the distilled water should be in excess when compared to aspirin. This can ensure all the acid in aspirin was hydrolyzed and even some distilled water was left for evaporation during boiling. After all, the reaction mixture in the conical flask would be transferred into a volumetric flask with more distilled water for dilution, so the amount of distilled water added was not that important to be accurate. Moreover, after the mixture in the conical flask was warmed, it ought to be cooled down, since the volume of the solution is different at different temperature. ...read more.


There are human errors when using the pipette or burette to measure the volume of solution, because the reading was not accurately obtained. In order to minimize the error, we should take the reading at our eye level, and from the bottom of the meniscus. Besides,when the reaction mixture of tablets and NaOH was boiling, some might be split out. The data would be affected and caused the inaccuracy. Therefore, we should regulate the distance between the bunsen burner and the flask to prevent the misture boiled too vigorously. Moreover, if the burette was not correctly rinsed of distilled water and sulphuric acid, the acid would be contaminated and reduce our accuracy of calculating.In order to minimize the error, we should rinse the burette with distilled water and then the sulphuric acid solution a few times. Conclusion The results obtained from titrimetric analysis of different aspirin show the price of 1g of 2-ethanoloxybenzoinc acid in different brands of aspirin,is shown as below, Brand Price of 1g of acid ($/g) Bayer 3.04 Cardiprin 4.84 Cartia 3.77 Halewool Chemicals Ltd. 0.951 As the price of 1g of 2-ethanoloxybenzoinc acid in Halewool Chemicals Ltd. is the cheapest and Cartia is the most expensive, Halewool Chemicals Ltd. aspirin tablets are the most worth to buy and the Cartia's is the least worth to buy. ...read more.

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