In this experiment, aspirin was synthesized by reacting salicylic acid with acetyl anhydride. This caused a chemical reaction that transformed the hydroxyl into acetyl. The melting point range of the substance was observed to be 128.5-137°C. The percentage yield of the final substance was determined to be 68.2%.
Aspirin Lab Report
The objective of this experiment is to prepare aspirin and determine the percentage yield. Aspirin is a derivative of salicylic acid; it is a mild analgesic that used to relief headaches and body aches (1). The drug restricts the production of prostaglandins, which are the chemical compounds that are required for blood clotting and sensitizing the nerves (2). Aspirin is one of the first drugs to be used widely and is still one of the most studied drugs in the world (1). The chemical formula of the drug is C9H8O4. The theoretical yield of aspirin is set at 2.748 g (2). It is calculated by adding the moles of salicylic acid and acetic acid. On the other hand, the percentage yield of aspirin is obtained by dividing the actual yield and theoretical and multiplying by 100.
Methods and Equipment
Ice; beaker; tap water; balance; plastic; tray; scoopula; salicylic acid; Erlenmeyer flask; graduated cylinder; acetic anhydride; pipet; H2SO4; stirring rod; vacuum filtration apparatus; Bunches funnel and litter paper; deionized water; hot plate; boiling chips; watch glass; crucible tongs.
- Always wear safety glasses.
- Avoid contact with sulfuric acid.
- Use heat when using acetic anhydride.
- Avoid contact with salicylic acid.
- Dispose of acids in appropriate container.
- Dispose of prepared aspirin in proper container.
- Do not ever eat anything in the lab.
- Fill a beaker with 60 ml of distilled water then place in an ice bath
- Weigh out 2.0-2.2 g of salicylic acid and record weight. Place in a 125 ml Erlenmeyer flask.
- Under the fume hood, prepare 4.0 ml and transfer into Erlenmeyer flask. Mix completely and record amount of acetic anhydride. While mixing, add 5 drops of sulfuric acid. Not warmth and stir until a clear solid develops.
- Add 10 ml of cold water from step 1 to a 10 ml of the mix in a graduated cylinder, and slowly add to Erlenmeyer flask while constantly stirring to dissolve clumps.
- Before connecting pressure tuning, assemble vacuum apparatus according to lab manual.
- Add 25 ml of cold distilled water to Erlenmeyer flask, stirring to dissolve clumps.
- Weigh and record the weight of filter paper and place in the funnel. Dampen with cold deionized water. Turn on aspirator to seal to funnel.
- Pour mixture into the funnel while swirling original container. Deionized water can be used to rinse out the flask to capture any remaining solid.
- While apparatus is still on, rinse the aspirin with 15 ml of cold deionized water and run for 10 minutes. While waiting, create a hot water both using boiling chips.
- Remove clump from tubing to release pressure. Turn off the water.
- Weigh and record the weight of watch glass. Place filter paper and crystals on top of glass, then place over hot water bath until crystals are dry
- Disassemble filtration apparatus and dispose of filtrate properly.
- Allow glass and crystals to cool and dry off condensation on the bottom of the glass. Weigh and record glass, along with its contents.
Several observations were made in the course of the experiment. Initially, there was nothing to report after placing the compounds in an ice bath. The mix was then weighed in a flask and the weight was found to be 2.02 g. 4.0 ml of acetic anhydride was added to the flask, which appeared slightly cloudy upon swirling. After adding sulfuric acid, the mixture became clear. Eventually, the mixture became cloudy again and thicker. The warmth was noted. No large solids were observed, and the swirling continued. Vacuum apparatus were assembled as per manual and water added to flask; very little solids were noted. The Filter paper weighed 0.37 g and a vacuum seal observed.
The majority of the mixture expelled and 3 ml of ionized water added to rinse out remaining solids.15 ml of ionized was water poured over top. The mixture allowed to dry for 10 minutes while a hot bath was prepared. The pressure was released and the water was turned off. The watch glass weight at this point was 31.10g. Crystals were then introduced into the watch glass and it was placed in the locker to dry till the next day. The vacuum was disassembled, filtrate disposed of in receptacle. The glass and contents weighed 33.55 g.
Molecule moles= (Mass of compound)/ (Molar Mass)
Acetic Anhydride: 102.09 g/ml
1.082 g/ml x 6ml= 6.492g acetic anhydride
Therefore, 6.492g/ 102.09 g/mol = 0.6359 moles
Salicylic Acid: 138.12 g/mol
Thus, 3g/138.12g= 0.02172 moles
Molecular mass of Aspirin= 180.16 g/mol
Therefore, 180.16 x 0.02172 mol- 3.913g aspirin
Percentage yield= 3.913g x 2.96g x 100= 76.65%
Discussion and Conclusion
In the experiment, pure aspirin was extracted after filtering out the excess reagent and impurities using filter paper. The melting point range of the substance was observed to be 128.5-137°C. The percentage yield of the final substance was determined to be 68.23%. It was observed that through the recrystallization of crude aspirin, the yield decreased from 76.65%. Nonetheless, a purer aspirin was developed as illustrated by the melting point. The theoretical melting point of aspirin is 134-136°C. A percentage era of 10.93% was obtained for the crude substance while that of the final product was 1.11%.
One source of error was the thermometer since it is possible the device inaccurately measured the melting range of the substance. Since the device was non-digital, the precise decimal points could be obtained visually. Another error was caused by the digital scale since it was highly sensitive. As a result, the results were affected by small interferences like air flowing in the lab.
If plausible, when measuring the melting point, the temperature should increase at a rate of 1-2 every sixty seconds when nearing the anticipated melting point to obtain a more precise range. In addition, humidity should be as low as possible. This is due to the sensitive nature of acetic acid when exposed to water vapor.