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Aspirin Tablets Lab

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Analysis of Aspirin Tablets Aim The objective of this experiment was to determine the percentage of 2-ethanoylhydroxybenzoic acid in Aspirin tablets. Theoretical Background 2-ethanoylhydroxybenzoic acid, also known as acetylsalicylic acid, is an analgesic (pain-killer) drug available under a commercial name of Aspirin. It is an ethanoate ester of salicylic acid, which is obtained from willow bark. Aspirin inhibits the production of prostaglandin synthase, an enzyme essential for production of prostaglandins, that cause swelling, fever, and are responsible for pain transmission to the brain [1]. Figure 1. Structural formula of 2-ethanoylhydroxybenzoic acid. The acetylsalicylic acid makes up only a percentage of Aspirin tablets. The aim of this lab session is to determine the percentage. The method chosen involves an analytical technique of volumetric analysis called back titration. Materials - weighing bottle - semi-analytical, electronic balance - 25cm3-pipette - four 250cm3-conical flasks - magnetic stirrer - 250cm3-standard flask - burette with a stand Table 1. Reagents used. ...read more.


However, an excess of sodium hydroxide was used in the hydrolysis. The excess of the sodium hydroxide was then titrated against hydrochloric acid of known concentration. Three trials were conducted and the average volume of HCl that was needed to neutralize NaOH was found to be 19.6cm3. Knowing the volume and the concentration of HCl (0.10 moldm-3), number of moles that reacted can be calculated. As the ratio of NaOH to HCl in the reaction was 1:1, the number of moles calculated was also a number of moles in of NaOH that took part in the reaction. For the titration only 25cm3 of NaOH were used, taken from the standard flask containing 250cm3 of a hydrolyzed solution. Therefore the number of moles of NaOH in the original, 250cm3 flask is ten times higher than the number of moles of NaOH in 25cm3. It was said that in hydrolysis 25cm3 (0.025dm3) of 1.0moldm-3 NaOH were used. The initial number of moles can be calculated. ...read more.


In fact, we do not know what substances were there, and we cannot assume that only acetylsalicylic acid was reacting. - Error could arise from the uncertainties of the measuring devices: pipettes, burettes and volumetric flask. (the error calculated to be 8.8%) - Error can also be caused by inaccurate determination of the end point in titration. The method used was based on the observation of the change in color of the indicator. - the human reaction time when turning the tap of the burette decreased the accuracy of the volume titrated Suggestions for Improvement - pH meter should be used to determine the end point of titration - mechanical pipettes can be used to decrease the error, because they usually have smaller uncertainties - more titrations should be carried out to pinpoint the most accurate average value and to minimize the possibility of random errors. - to decrease the uncertainty of the balance analytical one should be used instead of a semi-analytical one. ...read more.

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