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Analysis of the content in Aspirin Tablet

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1) Title: V3 Analysis of the content in Aspirin Tablet 2) Aim/Objective: To find out the mass of aspirin in each tablet by using back titration 3) Theory In this experiment, hydrolysis and back titration are carried out to determine the mass of the active ingredient aspirin in each aspirin tablet to see if it is the same as that stated on the package. Hydrolysis is a chemical process in which a molecule is cleaved into two parts by the addition of a molecule of water. Since aspirin (2-ethanoylbenzoic acid) can be readily hydrolysed using sodium hydroxide, forming the sodium salts of two weak acids, ethanoic acid and 2-hydroxybenzoic acid, and a water molecule, excess sodium hydroxide is used to react with aspirin in a conical flask initially, as illustrated in the following series of equations: CH3COOC6H4COOH(aq) + NaOH(aq)� CH3COOC6H4COO -Na+(aq) + H2O(l) CH3COOC6H4COO -Na+ (aq) + H2O(l) ? HOC6H4COO-Na+ (aq) + CH3COOH(aq) CH3COOH(aq) + NaOH(aq) � CH3COO-Na+(aq) + H2O(l) Overall reaction: CH3COOC6H4COOH(aq) + 2NaOH(aq)�HOC6H4COO-Na+(aq) + CH3COO-Na+(aq) +H2O(l) The hydrolysis is performed on a Bunsen flame to speed up the reaction. The kinetic energy of molecules becomes greater with an increase in temperature, colliding with each other faster. After warming for at least 10 minutes, all the 2-ethanoylbenzoic acid in the conical flask has reacted with sodium hydroxide, then the remaining sodium hydroxide can be determined using a titration set-up with Sulphuric acid in the burette, with the following equation: H2SO4(aq.) ...read more.


vi. While waiting for the warming, phenol red was tested. Three 75 cm3 beakers were used to carry sodium hydroxide, distilled water and Sulphuric acid. Two drops of phenol red was added into each of the beakers. The colours in each beaker were observed and the beakers were left behind. vii. The reaction mixture was cooled down in room temperature. Tap water was run on the outer wall of the conical flask to speed up the cooling process. viii. After that, the reaction mixture was transferred to a 250ml volumetric flask. Distilled water was added to the graduation mark. The flask was stoppered and inverted for several times. ix. 25ml of the diluted reaction mixture was pipetted into a conical flask using a 25cm3 pipette. x. 0.05M Sulphuric acid was added to the burette and the initial burette reading was taken. xi. Three drops of phenol red were added to the conical flask. The acid was run into the flask while the flask was swirled continuously. When the purple colour had changed to yellow, no more acid was added. The final burette reading was taken. xii. Procedures (ix) to (xi) were repeated for five times to obtain five consistent results. 7) Results: Trial 1 2 3 4 5 Final burette reading (cm3) 18.30 34.55 16.30 18.75 35.1 39.40 Initial burette reading (cm3) 1.65 18.30 0.00 2.45 18.75 23.30 Volume of H2SO4 used (cm3) ...read more.


Eventually the calculated mass of aspirin in each tablet would be heavier. In this experiment, there were some errors that might lead to a slightly wrong answer. For instance, it was assumed that only aspirin in the tablets had reacted with sodium hydroxide and that other contents in the tablets would not be hydrolysed. However, if such contents had reacted with sodium hydroxide, a greater amount of sodium hydroxide would be used for hydrolysis, leaving less sodium hydroxide in the conical flask afterwards. As a result, less Sulphuric acid would be used to neutralize sodium hydroxide in titration, giving a greater calculated mass of aspirin than actual again. On the other hand, since Sulphuric acid is quite hygroscopic, it would absorb water vapour from the air, diluting itself. If it is left to stand in air for too long, the volume of Sulphuric acid in the burette would become slightly larger and more diluted. So the number of moles of Sulphuric acid per cm3 would decrease and a slightly greater volume of Sulphuric acid would be required to neutralize sodium hydroxide. Then the calculated number of moles of sodium hydroxide used in hydrolysis would be smaller, and that the calculated mass of aspirin would be smaller. To eliminate this error, not only should the titration be carried out faster, the Sulphuric acid should also be kept in air as short as it could. 10) Conclusion: The mass of aspirin in each tablet was found to be 391.5 mg. ?? ?? ?? ?? Yu Wing Yee 6A(30) - 1 - ...read more.

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