Titration Analysis of Aspirin Tablets

Chemistry 12 12/Oct/2011 Titration- Analysis of Aspirin Tablets Objective: Determine the percentage of aspirin (acetylsalicylic acid) present in two different commercial tablets by titrating the solution with a base. Also determine whether the aspirin is a strong or weak acid according to the Bronsted- Lowry and Lewis theories and deduce the formula of the acid- base reaction. Independent Variable: The amount of base (NaOH) in moles that are needed to neutralize the solution. Dependent Variable: Percentage of aspirin (acetylsalicylic acid) found in each tablet.

Materials: * Balance * 2 aspirin samples from different brands * 50 cm3 conical flask * 10. 00cm3 of 95% alcohol * 0. 100 mol dm-3 sodium hydroxide * Phenolphthalein Procedure: 1. Bring samples of two different aspirin brands, note names, price, and the value of the aspirin per tablet indicated by the manufacturer. 2. Weight out accurately one tablet into a 50 cm3 conical flask and dissolve it in 10. 0cm3 of 95% alcohol. 3. Titrate with 0. 10 mol dm-3 sodium hydroxide solution using two drops of phenolphthalein solution as indicator in the first trial. 4.

For the next trials repeat steps 1 and 2, but instead of using an indicator use an electronic pH tester to measure the pH of the solution to determine when its neutral; (PH -7) . 5. Record data, ml used in titration to neutralize every aspirin trial. Raw Data Collection: Quantitative Data: Aspirin A: Trial| Aspirin Tablet| Uncertainty (ml)| Burette Reading NaOH(ml)| Resulting| Uncertainty (ml)| | (Grams)| | Initial (ml)| Uncertainty(ml)| Final (ml)| Uncertainty(ml)| NaOH (ml)| | 1| 0. 598| -+0. 001gr| 13. 50| -+0. 05ml| 40. 60| -+0. 05ml| 27. 10| -+0. 10ml| 2| 0. 603| -+0. 001gr| 11. 90| -+0. 05ml| 40. 80| -+0. 5ml| 28. 90| -+0. 10ml| 3| 0. 599| -+0. 001gr| 9. 50| -+0. 05ml| 37. 40| -+0. 05ml| 27. 90| -+0. 10ml| Average:| 0. 600| -+0. 001gr| 11. 63| -+0. 05ml| 39. 60| -+0. 05ml| 27. 97 | -+0. 10ml| Aspirin B: Trial| Aspirin Tablet| Uncertainty (ml)| Burette Reading NaOH (ml)| Resulting| Uncertainty (ml)| | (Grams)| | Initial (ml)| Uncertainty(ml)| Final (ml)| Uncertainty(ml)| NaOH (ml)| | 1| 0. 217| -+0. 001gr| 23. 60| -+0. 05ml| 28. 90| -+0. 05ml| 5. 30| -+0. 10ml| 2| 0. 223| -+0. 001gr| 28. 90| -+0. 05ml| 34. 50| -+0. 05ml| 5. 60| -+0. 10ml| 3| 0. 224| -+0. 001gr| 15. 10| -+0. 05ml| 20. 50| -+0. 05ml| 5. 0| -+0. 10ml| 4| 0. 229| -+0. 001gr| 20. 50| -+0. 05ml| 26. 20| -+0. 05ml| 5. 70| -+0. 10ml| Average:| 0. 223| -+0. 001gr| 22. 03| -+0. 05ml| 27. 53| -+0. 05ml| 5. 50| -+0. 10ml| Qualitative Data: Aspirin A: Bayer? s Aspirina 100 (pink) has 100mg. $3 (aprox. ) Aspirin B: Bayer? s Aspirina Protect (white) has 500mg. $2. 50 (aprox. ) Molarity of NaOH is 0. 10 ml/L -+0. 01 Molar mass of Aspirin (C9H8O4) is 180. 157g/mol. After dissolving the indicator in the distilled water it was still colorless, but when starting to add the base it turned to a slightly pink color, this assures that the compounds were reacting.

The burette gives a -+0. 05ml uncertainty. The measurements of weigh in grams of the tablets have a -+0. 001gr uncertainty. All materials were cleaned to eliminate errors in pH measurement. Data Process: Aspirin A Trial 1 NaOH needed to neutralize: 27. 10 ml NaOH| 1 L| 0. 10 mol NaOH| =| 0. 00271 mol NaOH -+0. 11ml| | 1000 ml| 1 L NaOH| | | | Grams of Aspirin: 0. 00271 mol NaOH| 1 mol C9H8O4| 180. 157 g C9H804| =| 0. 48823 g C9H8O4| | 1 mol NaOH| 1 mol C9H804| | | Percentage of aspirin: 0. 48823 g| X| 100%| /| 0. 100 g | =| 488. 23 % C9H804| Percent Uncertainty: 0. 10 ml | x| 100%| /| 27. 10 ml| =| -+ 0. 37%| 0. 01 g | x| 100%| /| 0. 598 g| =| -+ 0. 17 %| -+ 0. 37%| +| -+ 0. 17 %| =| -+ 0. 54%| Trial 2 NaOH needed to neutralize: 28. 90 ml NaOH| 1 L| 0. 10 mol NaOH| =| 0. 00289 mol NaOH -+0. 11ml| | 1000 ml| 1 L NaOH| | | | Grams of Aspirin: 0. 00289 mol NaOH| 1 mol C9H8O4| 180. 157 g C9H804| =| 0. 5207 g C9H8O4| | 1 mol NaOH| 1 mol C9H804| | | Percentage of aspirin: 0. 5207 g| X| 100%| /| 0. 100 g | =| 520. 65 % C9H804| Percent Uncertainty: 0. 10 ml | x| 100%| /| 28. 90 ml| =| -+ 0. 35%| 0. 001 g | x| 100%| /| 0. 603 g| =| -+ 0. 17 %| -+ 0. 35%| +| -+ 0. 17 %| =| -+ 0. 52%| Trial 3 NaOH needed to neutralize: 27. 90 ml NaOH| 1 L| 0. 0 mol NaOH| =| 0. 00279 mol NaOH -+0. 11ml| | 1000 ml| 1 L NaOH| | | | Grams of Aspirin: 0. 00279 mol NaOH| 1 mol C9H8O4| 180. 157 g C9H804| =| 0. 5026 g C9H8O4| | 1 mol NaOH| 1 mol C9H804| | | Percentage of aspirin: 0. 5026 g| X| 100%| /| 0. 100 g | =| 502. 64 % C9H804| Percent Uncertainty: 0. 10 ml | x| 100%| /| 27. 90 ml| =| -+ 0. 36%| 0. 001 g | x| 100%| /| 0. 599 g| =| -+ 0. 17 %| -+ 0. 36%| +| -+ 0. 17 %| =| -+ 0. 53%| Aspirin B Trial 1 NaOH needed to neutralize: 5. 30 ml NaOH| 1 L| 0. 10 mol NaOH| =| 0. 00053 mol NaOH -+0. 11ml| | 1000 ml| 1 L NaOH| | | | Grams of Aspirin: 0. 00053 mol NaOH| 1 mol C9H8O4| 180. 57 g C9H804| =| 0. 0955 g C9H8O4| | 1 mol NaOH| 1 mol C9H804| | | Percentage of aspirin: 0. 0955 g| X| 100%| /| 0. 100 g | =| 95. 48 % C9H804| Percent Uncertainty: 0. 10 ml | x| 100%| /| 5. 30ml| =| -+ 1. 89%| 0. 001 g | x| 100%| /| 0. 217 g| =| -+ 0. 46 %| -+ 1. 89%| +| -+ 0. 48 %| =| -+ 2. 35 %| Trial 2 NaOH needed to neutralize: 5. 60 ml NaOH| 1 L| 0. 10 mol NaOH| =| 0. 00056 mol NaOH -+0. 11ml| | 1000 ml| 1 L NaOH| | | | Grams of Aspirin: 0. 00056 mol NaOH| 1 mol C9H8O4| 180. 157 g C9H804| =| 0. 1009 g C9H8O4| | 1 mol NaOH| 1 mol C9H804| | | Percentage of aspirin: 0. 1009 g| X| 100%| /| 0. 100 g | =| 100. 9 % C9H804| Percent Uncertainty: 0. 10 ml | x| 100%| /| 5. 60 ml| =| -+ 1. 79 %| 0. 001 g | x| 100%| /| 0. 223 g| =| -+ 0. 45 %| -+ 1. 79 %| +| -+ 0. 45 %| =| -+ 2. 24%| Trial 3 NaOH needed to neutralize: 5. 40ml NaOH| 1 L| 0. 10 mol NaOH| =| 0. 00054 mol NaOH -+0. 11ml| | 1000 ml| 1 L NaOH| | | | Grams of Aspirin: 0. 00054 mol NaOH| 1 mol C9H8O4| 180. 157 g C9H804| =| 0. 0973 g C9H8O4| | 1 mol NaOH| 1 mol C9H804| | | Percentage of aspirin: 0. 0973 g| X| 100%| /| 0. 100 g | =| 97. 28 % C9H804| Percent Uncertainty: 0. 10 ml | x| 100%| /| 5. 40 ml| =| -+ 1. 85%| 0. 001 g | x| 100%| /| 0. 224 g| =| -+ 0. 45%| + 1. 85%| +| -+ 0. 45 %| =| -+ 2. 30%| Trial 4 NaOH needed to neutralize: 5. 70 ml NaOH| 1 L| 0. 10 mol NaOH| =| 0. 00057 mol NaOH -+0. 11ml| | 1000 ml| 1 L NaOH| | | | Grams of Aspirin: 0. 00057 mol NaOH| 1 mol C9H8O4| 180. 157 g C9H804| =| 0. 1027 g C9H8O4| | 1 mol NaOH| 1 mol C9H804| | | Percentage of aspirin: 0. 1027 g| X| 100%| /| 0. 100 g | =| 102. 69 % C9H804| Percent Uncertainty: 0. 10 ml | x| 100%| /| 5. 70 ml| =| -+ 1. 75%| 0. 001 g | x| 100%| /| 0. 229 g| =| -+ 0. 44 %| -+ 1. 75%| +| -+ 0. 44 %| =| -+ 2. 19 %| | Trial| Aspirin Tablet (Grams)| Percent of C9H804| AveragePercent| Aspirin A| 1| 0. 98| 488. 23 %| 503. 84 %| | 2| 0. 603| 520. 65 %| | | 3| 0. 599| 502. 64 %| | Aspirin B| 1| 0. 217| 95. 48 %| 99. 09 %| | 2| 0. 223| 100. 89 %| | | 3| 0. 224| 97. 28 %| | | 4| 0. 229| 102. 69 %| | Conclusions and evaluations: The percentage of aspirin in both of tablets was determined. The electronic pH tester made the development of the experiment much more efficient because the values became more exact, although it was not used in the first trials which showed a much larger difference in precision than accuracy, still the measurements show a pattern so they are in the same range.

Some of the results vary in unspecific patterns which display random error present, for example in trials 1 and 3 the mass of the aspirin tablet A is almost the same but the percent of acid in both varies in approximately 14 %. The same type of error can be seen in trial 4 in aspirin B which shows a similar percent of acid compared to trial 2 and both have a large difference in mass. The results show numerous differences between tablets so the conclusion we can get is that some tablets contain almost 100% acetylsalicylic acid.

When using the pH indicator some errors might have been produced because of the uncertainty about how “pink” the solution had to turn to become neutral, this was a random error. There was also random error when performing this experiment, the measurements on the different utensils might not have been exact so there might be small differences from the true value, apart from the uncertainties of the burette and other measuring devices we used. This is why in the aspirin B trials the measurements were more accurate because of the use of the electronic pH indicator.