Percentage Purity Of Aspirin Lab Report

Determination of the percentage purity of aspirin

Introduction
The aim of this experiment is to determine the percentage purity of 2-ethanoyl-hydrobenzoic acid (acetylsalicylic acid) in aspirin tablets. A known amount of standard sodium hydroxide solution is used in excess to hydrolyze a known mass of aspirin tablets:
CH3COOC6H4COOH(s) + NaOH(aq) → C9H7O4Na(s) + H2O(l)
The unused sodium hydroxide which remains is then titrated with standard nitric acid solution of 1 mol.
NaOH(aq) + HCl(aq) → NaNO3(s) + H2O(l)
The amount of alkali required for the hydrolysis can now be calculated and from the above equation, the amount of moles of acetylsalicylic acid which has been hydrolyzed can be found.
Research question | Independent variablesnumber…show more content…
Grind an aspirin tablet into a fine powder by using a mortar and pestle. Weigh accurately an aspirin powder. Determine the mass and record it on a data table.
2. Put aspirin powder in a beaker and pipette exactly 30 cm3 of a 1 M NaOH solution onto the powder. Stir the beaker in order to dissolve aspirin completely.
3. Add 3 drops of phenolphthalein to the beaker with aspirin powder and NaOH solution. NaOH solution would be in excess and thus prepare 1 M of HNO3 solution in burette, which will be used in back-titration.
4. Determine the end point of the back-titration when NaOH solution changes its color into pink. Record the results of at least three titrations. (Make a rough titration first).
5. Calculate the moles and mass of acetylsalicylic acid in an aspirin tablet. Determine the mass percentage of acid in a tablet.
Data collection VolumeV / cm3 | Titration trials | | | | 1 | 2 | 3 | 4 | 5 | Initial burette reading V / cm3±0.05 cm3 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | Final burette reading V / cm3±0.05 cm3 | 13.6 | 13.9 | 14.0 | 13.9 | 14.1 | Total tire V / cm3 ±0.1 cm3 | 13.6 | 13.9 | 14.0 | 13.9 | 14.1 |
Table 2 Volume of HNO3 required titrating NaOH in excess Mass of aspirin tablet ±0.001 [g] | 3.229 | 3.143 | 3.142…show more content…
Apart from the main reaction of aspirin there are 2 additional side reactions:

Side reaction 1 CH3COOC6H4COOH(s) + 2NaOH(aq) → HOC6H4COONa(s) + CH3COONa(s) + H2O(l)
Side reaction 2 CH3COOC6H4COOH(s) + 3NaOH(aq) → NaOC6H4COONa(s) + CH3COONa(s) + H2O(l)
In case of side reaction 1 aspirin reacts with 2 moles of NaOH which results in 2 times less number of moles reacted with acetylsalicylic acid. Then ratio of number of moles of acetylsalicylic acid and NaOH would be 1:2, which would present in 60% purity of aspirin. When aspirin reacts with 3 moles of NaOH the total ratio of number of moles of acetylsalicylic acid against NaOH would be 1:3, which would give around 30% purity.

Ways to improve experiment
In order to increase the accuracy of the result – if the results are consistent, the experiment becomes more accurate.
While dissolving aspirin tablets in beaker stirring could have been done to make sure all acetylsalicylic acid is dissolved.
A flow of human reactivity while determining the end point of titration could have caused some error and in order to prevent from that, slow titration should have been