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# the analysis of aspirin tablet

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Introduction

F.6A Lam Pik Sum (10) Title: the analysis of aspirin tablet Date: 6/10/2008 Objective: to determine the maximum amount of the active ingredient (acetylsalicylic acid) present in each aspirin tablet. Introduction In all pharmaceutical preparation, the manufacturer is required by law to state on the packaging the maximum amount of each active ingredient present. In many preparations the active ingredient will only form a small percentage of the pill or table as whole. For example, in the case of many tablets, the tablets would simply disintegrate into a powder unless additives were put in to assist in making the ingredients cohere into tablet form. In this experiment, you will have the opportunity to carry out a consumer survey on the aspirin content of a number of commercial preparations, to see whether the manufacturer's claim is justified or not. Acetylsalicylic acid (aspitin) can be readily hydrolysed by sodium hydroxide into the sodium salts of two week acids, acetic acid and salicylic acid. In this experiment, the hydrolysis is effected using an excess of sodium hydroxide, the excess being later found by titration with standard sulphuric acid. The equation for the hydrolysis reaction is: CH3.COOC6H4.COOH + 2NaOH � CH3.COONa + HO.C6H4.COONa + H2O We are now going to find out the amount of acetylsalicylic acid present in each aspirin tablet. As acetylsalicylic acid can be readily hydrolyzed by sodium hydroxide into the sodium salts of two weak acids, acetic acid and salicylic acid, so we can first add excess ...read more.

Middle

of H2SO4 used 15.0 cm3 14.8 cm3 14.8 cm3 14.8 cm3 Average volume of sulphuric acid used = (14.8 + 14.8 + 14.8) � 3 = 14.8 cm3 15.0 cm3 is rejected because this is just a trial. Titration table of the diluted reaction mixture with standard 0.08572M sulphuric acid Trial 1st titration 2nd titration 3rd titration Initial reading on the burette 3.1 cm3 14.7 cm3 9.9 cm3 22.0 cm3 Final reading on the burette 15.3 cm3 27.2 cm3 22.5 cm3 34.4 cm3 Volume of H2SO4 used 12.2 cm3 12.5 cm3 12.6 cm3 12.4 cm3 Average volume of sulphuric acid used = (12.5 + 12.6 + 12.4) � 3 = 12.5cm3 12.2 cm3 is rejected because this is just a trial. Calculation Standardization of sodium hydroxide H2SO4 + 2NaOH � Na2SO4 + H2O Volume of H2SO4 used: 14.8 cm3 Volume of NaOH used: 25.0 cm3 Mole ratio of H2SO4 to NaOH = 1:2 Number of mole of H2SO4 = 0.08572M x 0.0148 dm3 = 0.001268656 mol. Number of mole of NaOH = 0.001268656 mol. x 2 = 0.002537312 mol. Molarity of diluted NaOH = 0.00253712 mol. � 0.025 dm3 = 0.10149248M Molarity of original NaOH =0.10149248M x 10 = 1.0149248M Determination of amount of acetylsalicylic acid present in one aspirin tablet Total number of mole of NaOH = 1.0149248M x 0.025 dm3 = 0.02537312 mol. H2SO4 + 2NaOH � Na2SO4 + H2O Volume of H2SO4 used: 12.5 cm3 Volume of NaOH used: 25.0 cm3 Mole ratio of H2SO4 to NaOH = 1:2 Number of mole of H2SO4 = 0.08572M x 0.0125 dm3 = 0.0010715 mol. ...read more.

Conclusion

Oppositely, the reaction rate of reaction between the sodium hydroxide which is excess in the hydrolysis of aspirin and sulphuric acid is much faster. Therefore the end point is much easier to identify. 2) If phenol red is not available, what other indicator would you choose? Methyl orange and phenolphthalein can also be used in this titration. As this titration is a strong acid-strong base titration. When we study the titration curve of this titration (fig. a), we can see that the vertical portion of the curve is large. So almost all the indicators are suitable for detecting the end point of this titration. (fig. a) 3) Why must the heated mixture be cooled before transferred to volumetric flask? Volume of liquid will expend under high temperature. The volume of liquid inside the volumetric flask is exactly 250 cm3 when the liquid reach the graduation mark only when the liquid is in the room temperature. If we do not cool down the heated mixture before transferred to volumetric flask, then the volume of solution inside the volumetric flask is less than 250 cm3 when the solution reached the graduation mark. 4) Why do people consider aspirin as an equivalence to dibasic acid? The basicity of an acid is the number of ionizable hydrogen atom in each acid molecule. As the acetylsalicylic acid can be hydrolysed by sodium hydroxide into two week acids, which one mole of acetylsalicylic acid required two moles of sodium hydroxide to hydrolyse it, therefore aspirin as an equivalence to dibasic acid. End of Report ...read more.

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