Titration Analysis of Aspirin Tablets

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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| -+0.05ml| 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| 5.40| -+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%|
0.001 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...
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