Analysis of Asa in Aspirin Tablets

Topics: Standard deviation, Arithmetic mean, Mean Pages: 6 (1664 words) Published: March 22, 2012



In this experiment the concentration of acetyl salicylic acid (ASA) in an aspirin tablet will be determined. This can be done by dissolving a tablet in a strong base, NaOH, and titration it with a strong acid, HCl. The quantity was found to be about 75.5% of the weight of the tablet, or about 318 mg per tablet. This value tells the pharmaceutical companies how much to state the recommended dosage as based on how much ASA is needed to feel the headache and pain resistant effects. Also it can be used to state precautions for the customers based on the known LD50 value (200 mg/kg).


1) This experiment is used to find out if the quantity in an aspirin tablet is the same as what the pharmaceutical companies advertise. This is useful to the general public because people who use aspirin would like the amount of ASA in a tablet to be the true advertised amount. This experiment is also used to find out how much of the tablet is actually ASA and how much is filler. Most people are conscience about what they put into their body and do not wish to ingest unknown chemicals.

2) To find the concentration of ASA in aspirin a tablet is dissolved in a known concentration and volume of NaOH. This solution is then titrated with HCl to find how much excess NaOH is remaining in the flask.

3) Some advantages of the experimental method used in this experiment are that it is easy to do with equipment that is accessible and it yields results that are acceptable. The problem is that the results are not as accurate as they could be because of error due to the equipment. It is also difficult to judge neutralization points for each standardization and the determination of the ASA content. This problem leads to errors in volumes added in each titration and therefore an accurate volume cannot be truly achieved and in turn a true percent weight cannot be achieved either.


1) See page 28-30 of CHM 2354 Laboratory of Analytical Chemistry Laboratory Manual Winter 2012. Changes made:
* 2 trials completed for flask 1 and 3 in “Back Titration of the Excess NaOH”. * 2 trails completed in “Analysis of Aspirin Powder”

2) TABLE 1- Measurements made in preparation process
Flask Number| Mass of Potassium Hydrogen Phthalate used in Standardization of NaOH (g ±0.0001 g)| Volume of HCl used in Standardization of HCl (mL ±0.03 mL)| Mass of Aspirin Tablet used in Preparation of Acetyl Salicylate Solution (g ±0.0001 g)| Volume of NaOH used in Preparation of Acetyl Salicylate Solution (mL ±0.08 mL)| Mass of Aspirin Powder used in Analysis of Aspirin Powder (g ±0.0001 g)| Volume of NaOH used in Analysis of Aspirin Powder (mL ±0.08mL)| 1| 0.8936| 25| 0.4242| 100| 0.4199| 100|

2| 0.8698| 25| 0.4151| 100| ---| 100|
3| 0.8839| 25| 0.4242| 100| ---| 100|


1) TABLE 2- Measurements made in analyzing
Flask Number| Trial Number| Volume of NaOH used in Standardization of NaOH (mL ±0.05 mL)| Volume of NaOH used in Standardization of HCl (mL ±0.05 mL)| Volume of HCl used in Back titration of the excess NaOH (mL ±0.05 mL)| Volume of HCl used in Analysis of aspirin powder (mL ±0.05 mL)| 1| 1| 44.1| 25.56| 15.6| 15.94|

| 2| 42.5| 25.61| 15.99| 15.52|
| 3| 43.52| 25.66| ---| ---|
2| 1| ---| ---| 16.2| ---|
| 2| ---| ---| 15.57| ---|
| 3| ---| ---| 15.38| ---|
3| 1| ---| ---| 15.91| ---|
| 2| ---| ---| 15.6| ---|

2) TABLE 3- Calculated Values For Concentration of NaOH and HCl Trial Number| Concentration of NaOH Standard (mol/L)| Uncertainty of Concentration of NaOH Standard (±mol/L)| Mean Concentration of NaOH (mol/L)| Concentration of HCl Standard (mol/L)| Uncertainty of Concentration of HCl Standard (±mol/L)| Mean Concentration of HCl (mol/L)| 1| 0.0992| 0.1125| 0.0996...
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