Introduction:
First discovered in its modern form in 1897 by Felix Hoffman, aspirin has been used for over a century to reduce pain in medical patients. Aspirin is a controversial drug, as it has an adverse effect on many people, causing stomach lining deterioration, hives, swelling, and gastrointestinal bleeding. To understand why this is and better understand the chemical formula of C9H8O4, this experiment is useful in that we identify the main ingredient in aspirin, salicylic acid, and the lesser ingredient, acetic anhydride.
Salicylic acid has the formula C4H6(OH)COOH, with OH adjacent to the carboxyl group. Because of this salicylic acid is highly insoluble in water. Aspirin is created when the phenolic hydroxyl group of salicylic acid esterifies with acetic anhydride’s acetyl group. This means the COCH3 part of (CH3CO)2O reacts with the carboxyl group of salicylic acid to create also highly insoluble aspirin. This occurs in the presence of a catalyst, in this lab, sulfuric acid. The synthesis of aspirin creates the precipitate acetyl salicylic acid (aspirin) and a filtrate of acetic acid.
Filtering the raw aspirin is necessary to remove any unreacted acetic anhydride, sulfuric acid, and salicylic acid, as well as newly formed acetic acid. First, aspirin is insoluble in cold water, so it will remain when submerged, and any remaining acetic anhydride will be converted to acetic acid. All but the salicylic acid remaining can be completely removed through the addition of cold water and filtering with filter paper and a funnel. To completely remove the remaining salicylic acid further purification is required. The next process is called fractional crystallization. Heating the test tube in a warm water bath and adding ethanol to the test tube. The impure aspirin will dissolve, then later when cooling slowly will reform without any remaining impurities.
Melting point can be used as an excellent indicator of the purity of a substance. In most cases a lower melting point than accepted melting point indicates the impurity of a substance. The accepted melting point of aspirin is 136 degrees Celsius, and the melting point we received was closer 142 degrees Celsius, meaning that the aspirin remaining is still relatively impure.
Equipment Used:
Wax paper square
Electronic Scale
Large test tube
Safety glasses
Dropper bottle
10 ml graduated cylinder
Stirring rod
250 ml beaker
Metal ring
Ring stand
Bunsen burner
Test tube clamp
Metal gauze
Second Beaker
Funnel
Filter paper
Second Test tube
Test tube stopper
Water Heating Pan
Chemicals Used:
Powdered Salicylic Acid
MSDS- Salicylic acid powder is hazardous to skin, eyes, and lungs. For this reason it was important that during the lab we wore safety goggles, washed our skin quickly wherever touched by it, and did not ingest it.
Acetic Anhydride
MSDS- Highly hazardous to eyes, skin, and lungs. May produce burns or rashes. Wear safety goggles, wash skin quickly wherever touched with distilled water, and do not inhale or ingest.
Sulfuric Acid
MSDS- Extremely hazardous to skin, eyes, and lungs. Can produce burns, blisters, and when inhaled shortness of breath or respiratory inflammation. Wear safety goggles, wash any touched are with distilled water, do not inhale or ingest.
Water (liquid and solid)
Ethanol
MSDS- Damaging to skin, eyes, liver, heart, and stomach. Wear safety goggles, wash any touched areas with distilled water, do not inhale or ingest.
Procedure:
First, measure the mass of a 10cm square piece of paper. Set the balance ban so that it is 2 grams more than the paper, and put salicylic acid powder on the paper until the balance pan reads zero. Pour the measured salicylic acid powder into a test tube. At this point don your safety goggles and wear for remaining duration of the lab. Measure out 3ml of acetic anhydride using a 10ml graduated cylinder. Pour the 3ml into the test tube with the salicylic acid powder. Mix them by swirling. Add five drops of sulfuric acid and swirl.
Next, prepare a hot water bath by putting 60ml of water into a 250ml beaker and place the beaker over a Bunsen burner. Clamp the test tube tightly to the ring stand so that it is in the water but not touching the beaker. Boil the hot water bath for 5 minutes while stirring the test tube solution with a stirring rod. Remove the test tube from the clamps and cool it by running cold water over it, then, add 10ml ice water to the test tube. Crude aspirin will form at this point. Pour the mixture through filter paper and a funnel into a separate beaker. What is collected is the filtrate. Rinse the test tube with 5ml of distilled water. Filter again, rinse again, and filter a final time.
To purify the crude aspirin additional steps are required. First, move the crude aspirin from the filter paper to a new clean test tube. Add 7ml ethanol to the test tube. Re-create the hot water bath and clamp the test tube in until the aspirin dissolves. Add 15ml warm water to the test tube, if a solid forms; add more warm water until it dissolves. Stopper and label the test tube then let cool for one day. Finally, filter pure product and let dry overnight.
Calculations:
Reaction:
2.0g Salicylic Acid + 3.24g Acetic Anhydride = 0.0145 moles Aspirin + 0.0145 moles Water + 0.0395 moles Acetic Anhydride
Finding limiting reagent: Reaction is a 1 to 1 reaction
2.0g/138g = 0.0145moles Salicylic Acid (limiting)
3.24g/60g = 0.054 moles Acetic Anhydride (excess)
Theoretical Yield: 2.61 grams
0.0145 moles Aspirin x 180g/mol = 2.61g Aspirin
Percent Yield: 77%
2.01g/2.61g x 100% = 77.0%
Melting Point:
Accepted: 136.0 degrees Celsius
Experimental: 142.0 degrees Celsius
Percent Error: 4.41% (142-136)/136 x100% = 4.41%
Abstract:
The goal of the Aspirin Lab was to better understand the chemical properties of aspirin (C9H8O4) by studying all the ingredients and physical steps that go into its creation. We hypothesize that a solid aspirin precipitate will form at the conclusion of this experiment from the 1 to 1 molar reaction. Because the salicylic acid is the limiting reagent the 2.0 grams of it determine that the theoretical yield of aspirin is kept at 2.61 grams or 0.0145 moles. Using a test tube filled with the salicylic acid C4H6(OH)COOH, acetic anhydride (CH3CO)2O, and sulfuric acid, no precipitate will initially form, simply a solution. When placed in a hot water bath an aspirin precipitate forms in a water and acetic anhydride solution. The precipitate formed is “crude” aspirin and must then purified with ethanol. When the ethanol is mixed with the crude aspirin the test tube should be placed in another hot water bath for 5 minutes, then have warm added, then finally left to cool for a day. The final purified aspirin will not appear until it has cooled for such duration. We were able to create a sample of pure aspirin with a filtrate that was then filtered out. The results accurately corresponded with our hypothesis in that solid aspirin did form. However, we had only a 77% yield and a 4.41% percent error on our calculated 142 degrees Celsius melting pint. These statistics mean that some of the initial reactants did not react and some impurities remain in our “pure” product. During the experiment one unexpected thing did occur, a separate blue precipitate formed, similar in consistency to the white aspirin, and otherwise unnoticeable if not for the bluish hew. This may have been due to unclean equipment or exposure of the solution to something else during the process of aspirin creation. However, solid aspirin was produced successfully in large amounts and this experiment proved that heat has an effect on some reactions.
Conclusion:
Though only 77% of the theoretical yield was actually yielded, and an impure sample at that, this experiment was successful in proving several points. It proved that the limiting reagent, in this case salicylic acid, impacts theoretical as well as actual yield. It proved that heat does affect certain reactions, as several hot water baths, one ice water and one warm water injection, were required to initiate reactions over the course of the lab. To improve this lab in the future one thing that should be done is more thorough cleaning of all equipment prior to the labs beginning. From the initial reaction between salicylic acid and acetic anhydride to the filtering of the last filtrate from the purified aspirin, a light blue tint and byproduct was evident. This blue byproduct was probably the main source of impurities in the purified aspirin, driving the products melting point up the 6 degrees Celsius from 136 to 142. Furthermore, the test tube stoppers used to store the resting aspirins, both crude and purified, did not fit the designated test tubes perfectly, possibly allowing for leakage and access of outside impurities.
First discovered in its modern form in 1897 by Felix Hoffman, aspirin has been used for over a century to reduce pain in medical patients. Aspirin is a controversial drug, as it has an adverse effect on many people, causing stomach lining deterioration, hives, swelling, and gastrointestinal bleeding. To understand why this is and better understand the chemical formula of C9H8O4, this experiment is useful in that we identify the main ingredient in aspirin, salicylic acid, and the lesser ingredient, acetic anhydride.
Salicylic acid has the formula C4H6(OH)COOH, with OH adjacent to the carboxyl group. Because of this salicylic acid is highly insoluble in water. Aspirin is created when the phenolic hydroxyl group of salicylic acid esterifies with acetic anhydride’s acetyl group. This means the COCH3 part of (CH3CO)2O reacts with the carboxyl group of salicylic acid to create also highly insoluble aspirin. This occurs in the presence of a catalyst, in this lab, sulfuric acid. The synthesis of aspirin creates the precipitate acetyl salicylic acid (aspirin) and a filtrate of acetic acid.
Filtering the raw aspirin is necessary to remove any unreacted acetic anhydride, sulfuric acid, and salicylic acid, as well as newly formed acetic acid. First, aspirin is insoluble in cold water, so it will remain when submerged, and any remaining acetic anhydride will be converted to acetic acid. All but the salicylic acid remaining can be completely removed through the addition of cold water and filtering with filter paper and a funnel. To completely remove the remaining salicylic acid further purification is required. The next process is called fractional crystallization. Heating the test tube in a warm water bath and adding ethanol to the test tube. The impure aspirin will dissolve, then later when cooling slowly will reform without any remaining impurities.
Melting point can be used as an excellent indicator of the purity of a substance. In most cases a lower melting point than accepted melting point indicates the impurity of a substance. The accepted melting point of aspirin is 136 degrees Celsius, and the melting point we received was closer 142 degrees Celsius, meaning that the aspirin remaining is still relatively impure.
Equipment Used:
Wax paper square
Electronic Scale
Large test tube
Safety glasses
Dropper bottle
10 ml graduated cylinder
Stirring rod
250 ml beaker
Metal ring
Ring stand
Bunsen burner
Test tube clamp
Metal gauze
Second Beaker
Funnel
Filter paper
Second Test tube
Test tube stopper
Water Heating Pan
Chemicals Used:
Powdered Salicylic Acid
MSDS- Salicylic acid powder is hazardous to skin, eyes, and lungs. For this reason it was important that during the lab we wore safety goggles, washed our skin quickly wherever touched by it, and did not ingest it.
Acetic Anhydride
MSDS- Highly hazardous to eyes, skin, and lungs. May produce burns or rashes. Wear safety goggles, wash skin quickly wherever touched with distilled water, and do not inhale or ingest.
Sulfuric Acid
MSDS- Extremely hazardous to skin, eyes, and lungs. Can produce burns, blisters, and when inhaled shortness of breath or respiratory inflammation. Wear safety goggles, wash any touched are with distilled water, do not inhale or ingest.
Water (liquid and solid)
Ethanol
MSDS- Damaging to skin, eyes, liver, heart, and stomach. Wear safety goggles, wash any touched areas with distilled water, do not inhale or ingest.
Procedure:
First, measure the mass of a 10cm square piece of paper. Set the balance ban so that it is 2 grams more than the paper, and put salicylic acid powder on the paper until the balance pan reads zero. Pour the measured salicylic acid powder into a test tube. At this point don your safety goggles and wear for remaining duration of the lab. Measure out 3ml of acetic anhydride using a 10ml graduated cylinder. Pour the 3ml into the test tube with the salicylic acid powder. Mix them by swirling. Add five drops of sulfuric acid and swirl.
Next, prepare a hot water bath by putting 60ml of water into a 250ml beaker and place the beaker over a Bunsen burner. Clamp the test tube tightly to the ring stand so that it is in the water but not touching the beaker. Boil the hot water bath for 5 minutes while stirring the test tube solution with a stirring rod. Remove the test tube from the clamps and cool it by running cold water over it, then, add 10ml ice water to the test tube. Crude aspirin will form at this point. Pour the mixture through filter paper and a funnel into a separate beaker. What is collected is the filtrate. Rinse the test tube with 5ml of distilled water. Filter again, rinse again, and filter a final time.
To purify the crude aspirin additional steps are required. First, move the crude aspirin from the filter paper to a new clean test tube. Add 7ml ethanol to the test tube. Re-create the hot water bath and clamp the test tube in until the aspirin dissolves. Add 15ml warm water to the test tube, if a solid forms; add more warm water until it dissolves. Stopper and label the test tube then let cool for one day. Finally, filter pure product and let dry overnight.
Calculations:
Reaction:
2.0g Salicylic Acid + 3.24g Acetic Anhydride = 0.0145 moles Aspirin + 0.0145 moles Water + 0.0395 moles Acetic Anhydride
Finding limiting reagent: Reaction is a 1 to 1 reaction
2.0g/138g = 0.0145moles Salicylic Acid (limiting)
3.24g/60g = 0.054 moles Acetic Anhydride (excess)
Theoretical Yield: 2.61 grams
0.0145 moles Aspirin x 180g/mol = 2.61g Aspirin
Percent Yield: 77%
2.01g/2.61g x 100% = 77.0%
Melting Point:
Accepted: 136.0 degrees Celsius
Experimental: 142.0 degrees Celsius
Percent Error: 4.41% (142-136)/136 x100% = 4.41%
Abstract:
The goal of the Aspirin Lab was to better understand the chemical properties of aspirin (C9H8O4) by studying all the ingredients and physical steps that go into its creation. We hypothesize that a solid aspirin precipitate will form at the conclusion of this experiment from the 1 to 1 molar reaction. Because the salicylic acid is the limiting reagent the 2.0 grams of it determine that the theoretical yield of aspirin is kept at 2.61 grams or 0.0145 moles. Using a test tube filled with the salicylic acid C4H6(OH)COOH, acetic anhydride (CH3CO)2O, and sulfuric acid, no precipitate will initially form, simply a solution. When placed in a hot water bath an aspirin precipitate forms in a water and acetic anhydride solution. The precipitate formed is “crude” aspirin and must then purified with ethanol. When the ethanol is mixed with the crude aspirin the test tube should be placed in another hot water bath for 5 minutes, then have warm added, then finally left to cool for a day. The final purified aspirin will not appear until it has cooled for such duration. We were able to create a sample of pure aspirin with a filtrate that was then filtered out. The results accurately corresponded with our hypothesis in that solid aspirin did form. However, we had only a 77% yield and a 4.41% percent error on our calculated 142 degrees Celsius melting pint. These statistics mean that some of the initial reactants did not react and some impurities remain in our “pure” product. During the experiment one unexpected thing did occur, a separate blue precipitate formed, similar in consistency to the white aspirin, and otherwise unnoticeable if not for the bluish hew. This may have been due to unclean equipment or exposure of the solution to something else during the process of aspirin creation. However, solid aspirin was produced successfully in large amounts and this experiment proved that heat has an effect on some reactions.
Conclusion:
Though only 77% of the theoretical yield was actually yielded, and an impure sample at that, this experiment was successful in proving several points. It proved that the limiting reagent, in this case salicylic acid, impacts theoretical as well as actual yield. It proved that heat does affect certain reactions, as several hot water baths, one ice water and one warm water injection, were required to initiate reactions over the course of the lab. To improve this lab in the future one thing that should be done is more thorough cleaning of all equipment prior to the labs beginning. From the initial reaction between salicylic acid and acetic anhydride to the filtering of the last filtrate from the purified aspirin, a light blue tint and byproduct was evident. This blue byproduct was probably the main source of impurities in the purified aspirin, driving the products melting point up the 6 degrees Celsius from 136 to 142. Furthermore, the test tube stoppers used to store the resting aspirins, both crude and purified, did not fit the designated test tubes perfectly, possibly allowing for leakage and access of outside impurities.