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ANALYSIS OF ASPIRIN BY BACK TITRATION HNC APPLIED SCIENCE ANGELA COFRE 14 DECEMBER 2006 Analysis of Aspirin by Back Titration SUMMARY The purpose of the experiment was to determine the amount of aspirin in a tablet and to compare this with the amount specified on the label. The amount of aspirin calculated from the results obtained from titrimetric analysis to be 317 mg. The stated dose of the tablets on the manufactures label was 300 mg KEY WORDS Aspirin Back Titration Manufactures Labelling AIMS AND OBJECTIVES Objectives The objectives of this experiment are to determine the amount aspirin in a tablet and to compare this with the amount specified on the label. This was carried out using back titration. Aims The aims of the experiment were as follows: * Calculate the number of moles of HCL used in the reaction. * To determine the amount aspirin in an aspirin tablet and compare it with the amount specified on the label. * Calculate the number of moles of NaOH taken for hydrolysis. * Calculate the number of moles of NaOH used in hydrolysis. * Calculate the number of moles of aspirin. INTRODUCTION Aspirin is an acid and can be determined analytically by the method of back titration. ...read more.


The hydrochloric acid (0. l mol/dm3) was placed into a burette and the two samples were titrated until they became a pale yellow The level on the burette was noted at the start and at the end of the titration RESULTS First Titration Second Titration Start Burette Reading 0 14 Final Burette Reading 13.6 24.4 cm3 of HCI used 13.6 cm3 13.4 cm3 CALCULATIONS Volume of hydrochloric acid 3.6 cm3 + 13.4 cm3 = 27 cm3 Moles HCI = concentration X volume (dm3) 0.1 X 27 cm3 = 0.0027 Moles of HCL 1000 HCl + NaOH NaCl + H2O 1 of mole of excess Na OH is equal to 1 of mole of HCL So the moles of excess Na OH = 0.0027 Number of moles of Na OH in the original 60cm3 of 0.1 mol/dm3 solution. 0.1 X 60 cm3 = 0.006 Moles of Na OH 1000 Number of Moles of Na OH used in reaction with aspirin = original - excess 0.006 - 0.0027 = 0.0033 moles <==> 1 mole aspirin <==> 2 moles NaOH 0.00165 <==> 0.006 Moles Mass aspirin = moles x formula mass of aspirin = 0.00165 X 180 = 297 mg DISCUSSION In this experiment an aspirin tablet was reacted with a known excess amount of sodium hydroxide. ...read more.


would produce the most accurate and precise results. CONCLUSION The results obtained from titrimetric analysis of aspirin show that the tablet contains 297 mg of aspirin. The manufactures label that shows the tablet to contain 300mg of aspirin. 1 of mole of excess Na OH is equal to 1 of mole of HCL The ratio of sodium hydroxide to hydrochloric acid is 1:1; therefore, the molarity of diluted and stock sodium hydroxide solutions can be calculated by working out the number of moles of hydrochloric acid used. The number of moles of sodium hydroxide used in the reaction can be calculated by subtracting the number of moles of sodium hydroxide taken for the reaction by the number of moles of sodium hydroxide remaining after reaction Accuracy and precision of the measurements taken in the experiment can influence the data obtained. Experimental error in the results may have been due to the use of inaccurate glassware, calibration of measuring equipment which all a have % error. Measurements that will influence the calculations made from the data obtained, glassware not properly rinsed and dried before use, dirt and air on the analytical balance, or the acetyl salicylic acid not fully hydrolysed. ?? ?? ?? ?? Angela Cofre Page 1 20/06/2007 ...read more.

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4 star(s)

Overall this is a four star piece of work. It has an excellent introduction and plan but they could be in a better order to make it easier to understand as back titration can be hard to explain. Good set of results but there was an error in the first calculation which got carried over. Otherwise it is a good piece of work which shows all steps of the calculations clearly. Good analysis of results and suggestions for error given. Improvements would be to include a prediction and some more safety precautions. Good understanding overall.

Marked by teacher Patricia McHugh 08/04/2013

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