Given the balanced reaction between salicylic acid (C7H6O3) and acetic anhydride (C4H6O3) to produce ASA or acetylsalicylic acid (C9H8O4) and acetic acid (C2H4O2), the following experimental materials are provided: 5.00 g of pure salicylic acid, 7.14 g of acetic anhydride and 8 drops concentrated sulfuric acid as catalyst. After successful synthesis, the group was able to collect 5.25 grams of acetylsalicylic acid. (Atomic Given the balanced reaction between salicylic acid (C7H6O3) and acetic anhydride (C4H6O3) to produce ASA or acetylsalicylic acid (C9H8O4) and acetic acid (C2H4O2), the following experimental materials are provided: 5.00 g of pure salicylic acid, 7.14 g of acetic anhydride and 8 drops concentrated sulfuric acid as catalyst. After successful synthesis, the group was able to collect 5.25 grams of acetylsalicylic acid. (Atomic weights: C= 12 amu; H = 1 amu; O= 16 amu; density acetic anhydride = 1.08 g/mL). What is the PERCENTAGE in the experiment?
The Correct Answer and Explanation is :
To calculate the percentage yield of acetylsalicylic acid (ASA), we need to follow these steps:
Step 1: Write the balanced chemical equation
The balanced chemical equation for the reaction between salicylic acid (C₇H₆O₃) and acetic anhydride (C₄H₆O₃) is:
[
C₇H₆O₃ + C₄H₆O₃ \rightarrow C₉H₈O₄ + C₂H₄O₂
]
Step 2: Molar mass calculation
We need to calculate the molar masses of the substances involved:
- Salicylic acid (C₇H₆O₃):
[ (7 \times 12) + (6 \times 1) + (3 \times 16) = 84 + 6 + 48 = 138 \, \text{g/mol} ] - Acetic anhydride (C₄H₆O₃):
[ (4 \times 12) + (6 \times 1) + (3 \times 16) = 48 + 6 + 48 = 102 \, \text{g/mol} ] - Acetylsalicylic acid (C₉H₈O₄):
[ (9 \times 12) + (8 \times 1) + (4 \times 16) = 108 + 8 + 64 = 180 \, \text{g/mol} ]
Step 3: Calculate the theoretical yield
- Moles of salicylic acid (C₇H₆O₃):
[
\frac{5.00 \, \text{g}}{138 \, \text{g/mol}} = 0.0362 \, \text{mol}
] - Moles of acetic anhydride (C₄H₆O₃):
[
\frac{7.14 \, \text{g}}{102 \, \text{g/mol}} = 0.0701 \, \text{mol}
]
Since the molar ratio is 1:1 between salicylic acid and acetic anhydride, the limiting reagent is salicylic acid, which means the maximum amount of acetylsalicylic acid that can be formed is 0.0362 moles.
- Theoretical yield of acetylsalicylic acid (C₉H₈O₄):
[
0.0362 \, \text{mol} \times 180 \, \text{g/mol} = 6.516 \, \text{g}
]
Step 4: Calculate the percentage yield
The percentage yield is calculated using the formula:
[
\text{Percentage yield} = \left( \frac{\text{Actual yield}}{\text{Theoretical yield}} \right) \times 100
]
- Actual yield = 5.25 g
- Theoretical yield = 6.516 g
[
\text{Percentage yield} = \left( \frac{5.25 \, \text{g}}{6.516 \, \text{g}} \right) \times 100 = 80.5\%
]
Conclusion
The percentage yield of acetylsalicylic acid in this experiment is 80.5%.
This means that, compared to the theoretical amount of product that could be obtained, 80.5% of the expected acetylsalicylic acid was successfully synthesized. The deviation from the theoretical yield could be due to various factors, such as incomplete reactions, side reactions, losses during purification, or experimental error.