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Determination of the purity of commercial aspirin

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Introduction

DETERMINATION OF THE PURITY OF COMMERCIAL ASPIRIN Student: Vu Cuong Nguyen Lab partner: Tianren Yang Due date: Monday September 10th 2007 I. Aim: To determine the purity of commercial aspirin by performing the reaction between sodium hydroxide and aspirin. II. Data collection: Table 1.Titration of Aspirin Run 1 Run 2 Run 3 Initial volume of NaOH (�0.05ml) 12.65 23.45 22.70 Final volume of NaOH (�0.05ml) 23.45 34.15 33.50 Amount of NaOH used (�0.1ml) 10.8 10.7 10.8 Mass of Aspirin (�0.0005g) 0.2060 0.2020 0.2000 Volume of ethanol using (�0.1ml) 15.0 15.0 15.0 Table 2.Observation Process State of solution Obtained ethanol in the conical flask Colorless Dropped aspirin powder into ethanol white and pink Added bromthyol into the solution yellow The solution was titrated by sodium hydroxide light blue III. ...read more.

Middle

� 0.1 mol/L = 0.00107 mol � 0.9% --> naspirin (actual) = nNaOH = 0.00107 � 0.9% Percent purity = Run 3: % errormass of aspirin = naspirin (theoretical) = VNaOH (used) = (33.50 � 0.05ml) - (22.70 � 0.05ml) = 10.8 � 0.1ml % errorvolume of NaOH used = � 100% = 0.9% nNaOH = (0.0108 L � 0.9%) � 0.1 mol/L = 0.00108 mol � 0.9% --> naspirin (actual) = nNaOH = 0.00108 mol � 0.9% Percent purity = Average percent purity = IV. Conclusion: The average percent purity calculated is rather high, which is (96 � 1%), justifying that the aspirin sample is pure. ...read more.

Conclusion

It was very difficult to pinpoint the endpoint of the titration. This increased or decreased the amount of sodium hydroxide used for titration. Do as many runs as possible and then choose the best results among those collected. The 10-ml pipette was used to take 15ml of ethanol so we had to use it twice for getting 15ml of ethanol (the first time we obtained 10ml and then 5ml for the second). This increased the uncertainty. Use a pipette with larger scale (15ml or greater). As washed the burette by water, a slight amount of water left at the bottom of the burette, hence, affecting the amount of sodium hydroxide taken to titrate aspirin. With the first run, decrease the amount of sodium hydroxide needed for titrating aspirin a little bit. ...read more.

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