Introduction: Aspirin is one of the most widely used over-the-counter medications and is an important example of an organic acid. In Aspirin Tablet Analysis Experiment , you will determine the amount of aspirin present in a commercial aspirin tablet using a technique called titration.
Materials:
- Commercial aspirin tablet(s)
- 0.1 M NaOH solution (standard solution)
- Burette
- Pipette
- Indicator solution (e.g. phenolphthalein)
- Beaker or flask
- Stirring rod
- Distilled water
Procedure:
- Obtain a clean, dry burette and fill it with the 0.1 M NaOH solution. Record the initial burette reading.
- Obtain a clean, dry 250-mL beaker or flask and add approximately 50 mL of distilled water to it.
- Crush one aspirin tablet and add it to the beaker or flask with distilled water.
- Add a few drops of indicator solution (e.g. phenolphthalein) to the mixture and stir.
- Slowly add the NaOH solution from the burette to the mixture while stirring, until the solution changes color (indicating the endpoint of the titration). Record the final burette reading.
- Repeat the titration at least 2 more times and calculate the average volume of NaOH solution used.
- Use the balanced equation for the acid-base reaction and the volume and concentration of the NaOH solution to determine the amount of aspirin present in the tablet.
Precautions:
- Be sure to wear gloves and goggles during the experiment.
- Be sure to use clean, dry equipment and solutions.
- Do not ingest any of the solutions used in the experiment.
- Take care when handling the burette and pipette as they contain chemicals that can cause injury if spilled or broken.
- Be aware that aspirin tablets may contain other inactive ingredients such as binders, fillers, and dyes that could interfere with the results of the titration.
Worksheet for the students
Q.1 The initial burette reading for the acid-base titration experiment is 35.6 mL. The final burette reading after the titration is 45.2 ml. What is the volume of NaOH solution used in the titration? (answer: 9.6ml)
Q2. In an aspirin tablet analysis experiment, the initial burette reading is 30.0 ml and the final burette reading is 47.5 ml. How many ml of 0.1 M NaOH solution were used in the titration? (answer: 17.5ml)
Q3. The balanced equation for the acid-base reaction in an acid-base titration experiment is
HX + NaOH -> NaX + H2O. If the volume of NaOH solution used in the titration is 25.0 ml and its concentration is 0.1 M, what is the concentration of the unknown acid solution? (answer: 0.0025M)
Q4. In an aspirin tablet analysis experiment, the amount of NaOH used in the titration is 22.0 ml and the concentration of the NaOH solution is 0.1 M. How many moles of aspirin are present in the tablet? (answer: 0.002 moles)
Q5. In an aspirin tablet analysis experiment, the amount of aspirin present in the tablet is found to be 0.075 moles. If the tablet has a weight of 325 mg, what is the percent purity of the aspirin in the tablet? (answer: 23.07%)
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