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Experiment: Analysing molar mass of Aspirin

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Experiment: Analyzing molar mass of aspirin Introduction In 1899 the Bayer Company of Germany introduced the ethanoate ester of salicylic acid naming it, ?Aspirin?. Aspirin is an acid, it can be titrated with a base such as sodium hydroxide to the equivalence point. The following chemical equation describe the acid-base reaction that will be observed in this experiment. H-Aspirin + NaOH ------> Na-Aspirin + H2O (acid) (base) (salt) The above chemical equation is balanced as written. An indicator will be used to provide a way to visually determine the endpoint of the titration. Phenolphthalein changes from colourless to a faint pink while bromothymol blue changes from yellow to a faint blue at a pH of around 8. Aim To calculate the molar mass of Aspirin Hypothesis The chemical formula of Aspirin is C9H8O4. It can also be written as C6H5(OCOCH3)COOH. In this experiment, Aspirin, which is an acid, will react with sodium hydroxide, NaOH in an acid-base reaction to produce salt and water. This analysis makes use the fact that aspirin is a monoprotic acid and therefore reacts with NaOH according to the equation: C6H5(OCOCH3)COOH + NaOH ------> C6H5(OCOCH3)COO+Na- + H2O (acid) ...read more.


Repeat the experiment, but instead of phenolphthalein, use bromothymol blue as indicator. It is not necessary to clean out your burette of NaOH before you start the second experiment. Simply refill your burette and then start again. Data Collection and Processing Raw data Burette reading (± 0.05) ml Experiment A (with Phenolphthalein) Experiment B (with Bromothymol blue) 1st 2nd 3rd 1st 2nd 3rd Initial reading 0.0 16.0 31.9 0.0 15.1 30.9 Final reading 16.0 31.9 48.4 15.1 30.9 46.5 Volume used 16.0 15.9 16.5 15.1 15.8 15.6 Experiment Observation Initial pH Final pH A (Phenolphthalein) Color change from colorless to faint pink 4.3 8.7 B(Bromothymol blue) Color change from yellow to faint blue 4.2 8.6 Calculation 1. Experiment A C6H5(OCOCH3)COOH + NaOH ------> C6H5(OCOCH3)COO+Na- + H2O Average volume of NaOH used= = 16.1 ml No. of mol of NaOH= = 0.00161 mol Criterion C6H5(OCOCH3)COOH NaOH Equation mol 1 1 Real mol x 0.00161 mol No. of mol of C6H5(OCOCH3)COOH, x = 0.00161*1 = 0.00161 mol Mass of one tablet of aspirin, C6H5(OCOCH3)COOH= 300 mg or 0.3 g Molar mass of C6H5(OCOCH3)COOH = = = 186.33541 gmol-1 Percentage error= = 3.429% 1. ...read more.


This is the reason why phenolphthalein indicator is able to produce more accurate result than bromothymol blue. Evaluation There are some weaknesses that were detected throughout the experiment. Firstly, the volume of indicator are not fix in this experiment. Using drops is not really suitable as it may distort the volume of indicator in this experiment. The difference may not really big but it still can affect the final result. Secondly, the mixture of aspirin, C6H5(OCOCH3)COOH and sodium hydroxide, NaOH is not stirred during the titration. This may produce uneven and not uniform result as the NaOH is not totally mix with the aspirin. The neutralization process may only occur on the surface of the aspirin solution. Having said that, this experiment is successfully analyzing the molar mass of aspirin. The experimental value is close to the theoretical value. Further improvement In order to improve the results of the future experiments, several ways can be implemented. Firstly, the volume of indicator use should be fixed instead of using drops. By using this way, the level of uncertainty of the final results can be reduced. Besides that, the mixture of aspirin solution and NaOH need to be stirred throughout the titration process. More uniform results can be obtained by implementing this method. ...read more.

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