LIMITING AND EXCESS REACTANTS: HOW MUCH ASPIRIN CAN I MAKE?

1. What is reaction stoichiometry?

2. What are limiting and excess reagents, and which one controls the amount of products formed?

3. What were the objectives of this experiment?

4. How was reaction stoichiometry applied in the synthesis of aspirin?

5. How did you determine the quantities of limiting and excess reactants using stoichiometric calculations? Why is it important to balance the equation first before using stoichiometric calculations?

6. What lab techniques did you use in the synthesis of aspirin?

7. How did you determine the purity of your synthesized aspirin?

8. What procedural and chemical hazards were identified in this experiment, and what safety precautions did you implement to avoid these hazards?

 

II. Results Analysis

A. Data and Calculations

Show important results and calculations.

B. Discussion

Part I Planning and Carrying Out the Synthesis of Aspirin

1. Based on the expected physical properties of products, what type of reaction did you perform to synthesize a sample of aspirin? Show the balanced reaction equation.

2. What was the limiting reactant in your reaction? What was the excess reactant?

3. What was your assigned synthesis code? What was the mole ratio between the limiting and excess reactants?

4. What was your aspirin theoretical yield?

5. How was the synthesis apparatus set up? Briefly explain the procedure.

6. What indicators of chemical change were observed? What was their significance to the synthesis?

7. What was the mass of your dry crystal aspirin?

8. What was the experimental percent yield? What were the reasons for your low or high percent yield?

 

Part IIMelting Point Determination

1. What was the purpose of determining the melting point of aspirin?

2. How was the melting point determined? Briefly explain the procedure.

3. What changes indicated that the melting point had been reached?

4. What were the temperatures when melting was first noted and when all solid sample completely melted? What was the melting point of the synthesized aspirin?

5. What is the theoretical melting point of aspirin?

6. What was the percent error of your melting point determination?

 

Data Analysis: Effect of excess reactant amount on the percent yield and purity of aspirin 

1. Which Synthesis Code gives the highest percent yield?

2. Which Synthesis Code gives a high purity aspirin?

3. Based on your answer in analysis question 1, how many percent excess acetic anhydride will you use in Part III?

 

Part III Limiting and Excess Reactants Concept Application

If you were to prepare 2000 tablets of aspirin (at 325 mg/tablet),  

1. What is the target theoretical yield (grams)?

2. How many grams of salicylic acid will you need?

3. Based on your data analysis of Part I and II (see Data Sheet), how many grams of acetic anhydride will you need?

4. How much will it cost you to make the 2000 aspirin tablets?  

Use the Sigma Aldrich website (https://www.sigmaaldrich.com/united-states.html) to obtain the cheapest or lowest $/gram cost for salicylic acid and acetic anhydride (ACS grade reagents). Show all information references and calculations in your datasheet.

III. Conclusions

1. What reactions and general chemistry concepts were applied in this experiment? Briefly summarize the results.

2. What can be inferred from the melting point and physical appearance of your synthesized aspirin?  

3. Does the experimental melting point of your aspirin support your conclusion on the purity of your synthesized crystals?

4. Which of the three Synthesis Codes gave the highest percent yield?

5. Which of the three Synthesis Codes gave the high purity aspirin (low melting point percent error result)?

6. What do you recommend to improve the quality and yield of your synthesized aspirin? Based on the class data and results analysis, which mole ratio between limiting and excess reactant can improve the percent yield the purity of aspirin?

7. What is the practical application of this experiment?