Aspirin Synthesis Lab Analysis (2023)

Written by Lola

Before humans had the luxury of pain relievers and pharmaceutical drugs, many relied on the curing effects of willow tree bark, which was either chewed or boiled and used to relieve fevers and inflammation. Aspirin, acetylsalicylic acid, is a familiar drug, used for relieving cold and flu symptoms, fevers, and general aches and pains in the body, and, as made clear by its chemical formula, contains salicin – a chemical found in willow bark. In the following experiment, Aspirin was synthesized and analyzed in a laboratory setting in order to recognize the chemical process behind a common drug like aspirin and to relate it to the conceptual study of organic chemistry.

The initial step of the experimental process was the synthesis of Aspirin, which required the reaction of salicylic acid, acetic anhydride, and phosphoric acid to produce aspirin and acetic acid. This reaction is represented visually below:

Figure 1.1 Aspirin synthesis: chemical reaction involving salicylic acid and acetic anhydride as reactants and aspirin and acetic acid as products.

(Video) Laboratory Synthesis of Aspirin

As shown in the above reaction, phosphoric acid, H3PO4 acts as a catalyst in the initial mixture of the reactants in order to speed up the reaction.

After aspirin synthesis was complete, the aspirin was analyzed using both IR and NMR spectrometers in order to determine the hydrogen atoms and organic functional groups present in the synthesized aspirin and to verify the overall identity of the aspirin.

To begin the experiment, 2.00 g of salicylic acid (formula weight of 138.12 g/mol), 5.0 mL of acetic anhydride (density of 1.082 g/mL), and 5 drops of phosphoric acid were mixed in a 150mL Erlenmeyer flask, which was then placed in a beaker containing de-ionized (DI) water heated to 75°C on a hot plate. Salicylic acid was a white, chalky powder; acetic anhydride a clear, colorless liquid; and phosphoric acid a clear, yellow-tinted liquid. The final mixture, a clear, colorless liquid, was stirred occasionally and the temperature of the water was monitored. After 15 minutes of maintained heat, the flask was removed from the water and 2 mL of DI water was added, producing an aromatic vapor. After the vapor dissipated, a second volume of DI water, 20 mL, was added. The flask was then scratched on the bottom and placed in an ice bath to encourage crystallization. While the mixture in the flask cooled, a vacuum filtration system was created, and once crystallization occurred, the mixture was poured through the system so as to pull the liquid in the mixture through to the flask, leaving white, powdery crystals on the filter paper. The crystals were then washed three times with the vacuum using 5 mL amounts of DI water. Lastly, the crystals were scraped into a labeled, pre-weighed beaker and placed in a 40°C oven for 46 hours to dry. After the crystals were completely dry, the beaker was weighed a second time, including the crystals, in order to obtain the actual yield of synthesized aspirin: 2.1 g. This value was used, along with the theoretical yield value, to calculate the percent yield of the synthesized aspirin: 81%.

Caution – acetic anhydride, salicylic acid, and phosphoric acid are all toxic chemicals and should not come into contact with the skin. CDCl3, used later for spectroscopy, is also a toxic chemical.

Next, NaOH was used to titrate commercial aspirin tablets – one tablet of aspirin, weighing 325 mg, was dissolved in methanol, and then 10 mL of DI water and 4 drops of phenolphthalein (indicator) were added. This mixture was generated a total of three times, so as to have three separate flasks with identical mixtures for three trials. A 50 mL burette was then washed with one 5 mL portion of NaOH, then filled to near the 0 mark of the burette with NaOH. The starting reading of NaOH was recorded. Titration was then performed in three trials, each by adding NaOH to the mixture in the flask until the mixture turned light pink and maintained this color for 15 seconds. The end point reading of NaOH was recorded. The moles of aspirin used was calculated and incorporated into a calculation of the average concentration of NaOH (mol/L) using the second and third trial amounts of NaOH. These trials’ pink solution were light, while the first trial’s pink solution was too dark, and resulted in a smaller concentration of NaOH.

To finish the experiment, three titration trials were performed using the synthesized aspirin. 0.3 g of aspirin was weighed by difference and dissolved in 5 mL of methanol in an Erlenmeyer flask for each trial. DI water and four drops of phenolphthalein were added, and the same process of titration was used. All three synthesized aspirin titrations yielded a light pink color for 15 seconds, thus each trial was successful and used in calculations.

(Video) Synthesis of Aspirin Lab

The synthesized aspirin was also used in two different types of spectroscopy: NMR and IR. NMR was the first to be tested: a glass NMR tube was filled with the aspirin sample to a height of approximately 0.5 cm and 0.6 mL of CDCl3 was added in order to avoid large protein peaks. The solution was then inserted into an Anasazi 60 MHz FT-Nuclear Magnetic Resonance Spectrometer and the spectrum was printed. During IR spectroscopy, a pinhead sample of aspirin was placed on the diamond ATR plate of a Nicolet iS10 Infrared Spectrometer and the spectrum was printed.

The trial results of the commercial aspirin titrations are listed below:

g commercial aspirin


NaOH Concentration

(mol NaOH/L)

.325 g

38.36 mL

4.7 x 10-2 mol/L (not used)

.325 g

36.35 mL

5.0 x 10-2 mol/L

.325 g

36.30 mL

5.0 x 10-2 mol/L

As mentioned in the experimental section, the first trial was not used in the final calculation of the average NaOH concentration. Thus, the average concentration of NaOH was 5.0 x 10-2 mol/L.

The trial results of the synthesized aspirin titrations are listed below:

g product aspirin


Molecular Weight (g aspirin/mol)

.31 g

36.95 mL

1.7 x 102 g/mol

0.3193 g

36.89 mL

1.8 x 102 g/mol

0.313 g

36.45 mL

1.7 x 102 g/mol

By combining all three molecular weights, the average molecular weight was 1.7 x 102 g/mol.

(Video) Synthesis and Analysis of Aspirin (experiment 1)

The spectrum attained from NMR spectroscopy of synthesized aspirin is below:

Figure 2.1 The NMR spectrum of synthesized aspirin displays a peak 2.4 PPM and a range of peaks from 7 PPM to 8.3 PPM

The spectrum attained from IR spectroscopy is below:

Figure 2.2 The IR spectrum of synthesized aspirin displays two peaks in the 1650 cm(^-1) to 1850 cm(^-1) range at 1679.70 cm(^-1) and at 1749.46cm(^-1)

(Video) Lab 11 - Synthesis of Aspirin Prelab

The table below lists NMR standards from several NMR spectra of functional group chemicals:

Functional Group

Reference Compounds

NMR peak for functional groups (PPM range)

Saturated hydrocarbon


acetic acid

propionic acid



phenyl acetate

methyl benzoate

ethyl acetate



2.0 PPM

2.1 PPM

2.2-2.6 PPM

2.1 PPM

1.7 PPM

2.3 PPM

3.4 PPM

2.0 PPM

2.2 PPM

1.4 PPM

Aromatic hydrocarbon

benzoic acid

salicylic acid


phenyl acetate

methyl benzoate



6.8-7.1, 7.4-7.7 PPM

6.7-8.1 PPM

6.3-7.2 PPM

7.0-7.5 PPM

6.8-7.7 PPM

7.2 PPM

6.7-7.5 PPM

Carboxylic acid

acetic acid

propionic acid

salicylic acid

benzoic acid

11.0 PPM

9.8 PPM

9.1 PPM, 10.3 PPM

10.7 PPM

The table below lists IR standards from several IR spectra of functional group chemicals:

Functional Group

Reference Compounds

IR peak from 1650-1850 cm-1





1709.33 cm-1

1714.82 cm-1

1681.32 cm-1

Carboxylic acid

acetic acid

propionic acid

salicylic acid

benzoic acid

1704.69 cm-1

1708.51 cm-1

1652.36 cm-1

1678.23 cm-1


phenyl acetate

methyl benzoate

ethyl acetate

1761.26 cm-1

1718.99 cm-1

1736.81 cm-1

There are several things to be taken away from the collected data in regards to the purity of the synthesized aspirin sample. First, an average molecular weight of 1.7 x 102 g/mol was derived from titrations (table 2.2). This value, compared with the molecular weight of commercial aspirin, C9H8O4, will demonstrate the difference in purity. The molecular weight of commercial aspirin is 180.1574 g/mol, approximately 10 g/mol higher than that of the synthesized aspirin. Thus, the synthesized aspirin was close to the identity of commercial aspirin, but not exactly, so it can be concluded that the synthesized aspirin was not entirely pure.

Each spectrometer yields further results regarding the purity of the aspirin. NMR spectra reflect the presence of hydrogen atoms, or protons, in a substance. The two starting materials in the aspirin synthesis reaction were acetic anhydride and salicylic acid. In the reaction between acetic anhydride and water, a gas was released that gave off a smell similar to that of vinegar. This gas was acetic acid; an end product in the aspirin synthesis reaction, thus the NMR spectrum of acetic acid was analyzed. It is known from the NMR spectrum of acetone, which is a reference compound with only one type of hydrogen (that belonging to CH3), that the peak at 2 PPM in the acetic acid spectrum pertains to CH3 (table 2.3). Therefore, the second peak from acetic acid pertains to the hydrogen the carboxylic acid, at 11.0 PPM. Because the NMR spectrum of the synthesized aspirin sample does not have a peak at 11.0 PPM, it can be concluded that there is no leftover acetic acid in the final product. By using acetic acid’s spectrum as a reference for salicylic acid, it is known that the peak at 10.3 PPM is probably the hydrogen belonging to the carboxylic acid in the structure. This leaves a peak at 9.1 PPM and a range of peaks from 6.7 to 8.1 PPM. Because the range of peaks matches (table 2.3), with the aromatic hydrocarbon peaks, this range must represent the hydrogen atoms present in the benzene ring, and by process of elimination, the final peak at 9.1 PPM must be the remaining hydrogen in the alcohol in the structure of salicylic acid. Because the synthesized aspirin spectrum does not have a peak at 9.1 PPM to represent alcohol or, as mentioned previously, at 10.3 PPM to represent carboxylic acid, the synthesized aspirin has no leftover salicylic acid present. From these two analyses, it can be concluded that no reactants remain in the final product aspirin, and that the functional groups present in the synthesized aspirin NMR spectrum are CH3 and aromatic hydrocarbon (benzene).

IR spectra display the wavenumbers at which reference compounds are transmitted. Looking again at the starting materials of the aspirin synthesis reaction, acetic acid and salicylic acid, each compound has one peak in the 1650 to 1850 cm-1 range on their IR spectra. Acetic acid has a peak at 1704.69 cm-1 and salicylic acid has a peak at 1652.36 cm-1. The two peaks in the 1650 to 1850 cm-1 range in the synthesized aspirin IR spectrum (figure 2.2) are at 1679.70 cm-1 and 1749.46 cm-1. Because neither of these values matches with those values on the acetic acid and salicylic acid IR spectra, it can be concluded that neither of the starting materials are present in the synthesized aspirin sample. By matching the synthesized aspirin peak at 1749.46 cm-1 to the peak values in table 2.4, it is evident that this peak represents the ester in the structure of aspirin. The remaining peak value from the synthesized aspirin is 1679.70 cm-1, which corresponds with values in both the ketone and carboxylic acid sections of table 2.4. However, looking at the structure of synthesized aspirin, the remaining component that has not been identified but is present in the structure is carboxylic acid. Thus, the peak at 1679.70 cm-1 represents a carboxylic acid.

(Video) Aspirin Synthesis

To summarize, both spectrometers give significant evidence suggesting the purity of the synthesized aspirin product. First, based on the NMR spectra of the starting materials in the aspirin synthesis reactions, it is conclusive that there are no starting materials present in the final product, and that the peaks on the NMR spectrum of synthesized aspirin show the hydrogen atoms in CH3 and aromatic hydrocarbon in the final structure. Additionally, based on the IR spectra of the starting materials in the reaction, it is further conclusive that they are not present in the final product, and that the peaks on the IR spectrum of synthesized aspirin show functional groups ester and carboxylic acid in the final structure.

Overall, the purpose of this lab, to synthesis aspirin and prove its purity using organic functional groups, was accomplished successfully. The final product of synthesized aspirin contained no starting materials and its molecular weight was relatively close to that of pure aspirin, thus it was almost entirely pure.

I would like to acknowledge a few people who helped make this scientific paper better than it would have been: Kevin Braun, for supplying the materials of the experiment, assisting with the experiment, teaching NMR and IR spectroscopy, and reviewing the results of the experiment; *****, for assisting me with the interpretation of the NMR and IR spectra; ******, for assisting me with the IR worksheet assignment, experimental calculations, and proofreading; ********, for assisting me with the NMR worksheet assignment; and ******, for proofreading this paper.


What were the lab errors in the synthesis of aspirin? ›

The possible sources of error in the experiment were: (1) the collected crude aspirin was not dried and immediately subjected to another recrystallization; (2) the Erlenmeyer flask used was not clean, and; (3) the solution did not heat in a steam bath for 15 minutes.

What is the conclusion of the aspirin synthesis lab report? ›

Conclusion: A total of 2.169 grams of pure aspirin was synthesize out of a possible yield of 2.52 grams. Thus, there was 86.07% product yield. Acetylation of salicylic acid makes aspirin less acidic and therefore less damaging to the digestive system of the human body.

How is aspirin prepared lab answers? ›

To prepare aspirin, salicylic acid is reacted with an excess of acetic anhydride. A small amount of a strong acid is used as a catalyst which speeds up the reaction. In this experiment, sulfuric acid will be used as the catalyst. The excess acetic anhydride will be quenched (reacted) with the addition of water.

What can be the reason for 100% yield in aspirin synthesis experiment? ›

If it is above 100%, it may be because your aspirin was not completely dried.

What were possible sources of error in this lab? ›

Physical and chemical laboratory experiments include three primary sources of error: systematic error, random error and human error. These sources of errors in lab should be studied well before any further action.

What are the sources of error in synthesis lab? ›

Lab Errors
  • Spilling.
  • Dropping equipment.
  • Not cleaning equipment.
  • Ignoring directions.
  • Writing an incorrect number.
  • Hitting the wrong key on a calculator.
  • Not paying attention to units/labels.

What is the end point of aspirin analysis? ›

Slowly titrate the aspirin with the NaOH. You should vigorously swirl (not shake) the flask continuously to ensure the solution is homogeneous. The end point is the faintest possible pink color that you can perceive. Ideally, one drop of NaOH should change your solution from colorless to bright pink.

What was the purpose of the aspirin experiment? ›

Your two primary objectives in this experiment will be to synthesize and analyze aspirin. There is more than one way to synthesize aspirin; in this experiment, you will react acetic anhydride with salicylic acid in the presence of phosphoric acid (which acts as a catalyst). The reaction equation is shown below.

What is the objective of the aspirin lab report? ›

The objective of this experiment is to enable us to conduct the synthesis of aspirin, reinforce the skills of recrystallisation and reinforce the technique of melting point determination. It is carried out to form ester from an acid and an alcohol.

What factors affect the yield and purity of aspirin in laboratory preparation? ›

The yield and purity of the aspirin de- pended on the rate of the reaction. The three factors affecting the rate of reaction in this exploration were the temperature, the concentration of the reactants, and the concentration of the catalyst.

What is the result for preparation of aspirin? ›

Aspirin can be made by reacting salicylic acid with acetic acid in the presence of an acid catalyst. The phenol group on the salicylic acid forms an ester with the carboxyl group on the acetic acid. However, this reaction is slow and has a relatively low yield.

How do you determine the amount of acetylsalicylic acid in an aspirin lab report? ›

To determine the amount of acetylsalicylic acid present in an aspirin tablet, the easiest process would be to dissolve a tablet and titrate it with a base. Titration uses a solution of known concentration to react completely with an analyte to determine its concentration or amount.

What are two possible reasons why your yield of aspirin was not 100%? ›

The reasons why the percent yield could be less than 100% is due to loss of the aspirin in the glassware. Another possible source for decrease in the yield is unreacted reactants which would affect the amount of product (aspirin) generated.

What is one reason why the yield from an experiment is rarely 100%? ›

Usually, percent yield is lower than 100% because the actual yield is often less than the theoretical value. Reasons for this can include incomplete or competing reactions and loss of sample during recovery.

What factors cause the percent yield to more than 100%? ›

It is only possible to get a percentage yield greater than 100 percent if the product is contaminated with impurities or if all the solvent from the reaction mixture has not been dried off.

What is the most common lab error? ›

The most common lab errors in the collection of the samples and reporting are: Wrong labeling of the sample. The technique of the blood sample: This is very important to follow an excellent technique to collect good quality blood.

What are the causes of error analysis? ›

The two major causes of error, coined by the error analysis approach, are the Interlingual error which is an error made by the Learner's Linguistic background and Native language interference, and the Intralingual error which is the error committed by the learners when they misuse some Target Language rules, ...

What percentage error is acceptable? ›

For a good measurement system, the accuracy error should be within 5% and precision error should within 10%.

What are the 5 most common errors occurring in your laboratory? ›

Some common laboratory errors
  • patient ID error.
  • lost sample.
  • sample delayed in transit.
  • contaminated samples.
  • wrong test performed.
  • test performed inconsistent with the written procedure.

What are the sources of uncertainty in an experiment? ›

There are two sources of experimental uncertainties: systematic effects and random effects. Experimental uncertainties are distinct from personal errors.

What is an acceptable error in an experiment? ›

This helps you evaluate your results and compare them against other people's values. The difference between your results and the expected or theoretical results is called error. The amount of error that is acceptable depends on the experiment, but a margin of error of 10% is generally considered acceptable.

What is the purpose of adding water at the end of aspirin synthesis? ›

After the reaction takes place, water is added to destroy the excess acetic anhydride and cause the product to crystallize. The aspirin is then collected, purified by recrystallization, and its melting temperature measured.

What is the chemical analysis of aspirin? ›

Aspirin (Acetylsalicylic acid)

Acetylsalicylic acid commonly known as Aspirin is a prototypical analgesic with the chemical formula C9H8O4. It is also known as aspirin or 2-Acetoxybenzoic acid. It appears as a crystalline powder which is colourless to white.

How does pH affect aspirin hydrolysis? ›

The acetylsalicylic acid hydrolysis reaction is a first order reaction, proven by the value of the reaction velocity constant relatively constant. In this experience it is observed that the acetylsalicylic acid hydrolysis reaction is faster at acid pH and at 60 ° C.

What is the abstract of aspirin experiment? ›

Abstract: The objective of this experiment was to synthesize aspirin from salicylic acid and acetic anhydride. The general theory behind this experiment was to study the synthesis of a drug from organic materials. During the experiment, esterification had occurred between reactants salicylic acid and acetic anhydride.

What is the major impurity in aspirin synthesis? ›

Salicylic acid is a major hydrolytic degradation product of aspirin, responsible especially for gastric irritation during oral aspirin administration. This impurity was investigated in 12 different brands of aspirin formulation readily available in our locality.

What are the most likely impurities present in the sample of aspirin? ›

The main impurity in our crystallized aspirin will be salicylic acid. Salicylic acid will co-precipitate with the aspirin if the procedure is done too quickly. The first method we can use to determine the purity of our sample is the determination of its melting point.

What causes low yield in aspirin synthesis? ›

One contributing factor for the low yield is that some crystals were lost during the filtration process. There was also a small amount of crystals lost when the crude product was transferred to the new 50 mL Erlenmeyer flask.

What is the most common byproduct in the synthesis of aspirin? ›

The byproduct of the synthesis of aspirin is acetic acid. During the reaction of salicylic acid with acetic anhydride for the synthesis of aspirin, acetic acid comes out to be the byproduct with formula CH3 COOH.

What is the percent purity of aspirin lab? ›

Standards for medications are defined by the United States Pharmacopeia (USP) (6). Aspirin tab- lets must contain not less than 95 percent and not more than 105 percent of the labeled amount of CgH8O4 (acetylsalicylic acid). The same percentage applies for CgH9NO2 (acetaminophen).

How do you calculate the purity of an aspirin sample? ›

It is calculated by dividing the amount of pure substance to the sample and then multiplying the ratio with 100.

What method of analysis does the analysis of acetylsalicylic acid follow? ›

A high-performance liquid chromatography with mass spectrometry (LC-MS/MS) method was developed and validated for the accurate determination of acetylsalicylic acid in human blood.

What steps could you take to improve the yield of aspirin in an experiment? ›

Put the flask in an ice bath to hasten crystallization and increase the yield of product. If crystals are slow to appear, it may be helpful to scratch the inside of the flask with a glass rod. Collect the aspirin by vacuum filtration.

What would happen to your percent yield if the aspirin you prepared was not dried completely? ›

If the filtered aspirin product is not fully dried then it will still contain significant water content. This water content will add to the actual yield of aspirin. Therefore it will increase the percent yield erroneously. If the product is excessively wet this may even cause a percent yield over 100%.

What two impurities are most likely to be present in the aspirin that you prepared? ›

Therefore, the two impurities that are most likely to be present in the aspirin are salicylic acid and acetic acid.

Does percent yield indicate the success of an experiment? ›

Chemists need a measurement that indicates how successful a reaction has been. This measurement is called the percent yield.

Which would result in a percent yield below 100 %in an experiment? ›

Side reactions and reaction byproducts can result in less than 100% yield, as well as human error.

Why is there a need to calculate percent yield for an experiment? ›

Percent yield will indicate how much product is left-over and help you formulate a plan to create less waste during the chemical reactions.

What factors affect the yield and purity of aspirin in the laboratory? ›

The yield and purity of the aspirin de- pended on the rate of the reaction. The three factors affecting the rate of reaction in this exploration were the temperature, the concentration of the reactants, and the concentration of the catalyst.

What are the hazards of synthesis of aspirin? ›

Risk Assessment

Acetylsalicylate and salicylic acid are combustible and harmful if swallowed. Acetic anhydride is corrosive, acid, can cause severe burns and is highly flammable. Ethanol is highly flammable.


1. Synthesis of aspirin
(Roxi Hulet)
2. Aspirin Synthesis Introduction
(Stoddard Tutoring)
3. Aspirin - Part 1: Synthesis.MP4
4. Online Aspirin Synthesis Lab
5. Introduction to Lab 5 - Aspirin Synthesis
(Jen Stallings)
6. Synthesis and Analysis of Aspirin (experiment 2)
(UP Chemistry Department)


Top Articles
Latest Posts
Article information

Author: Lidia Grady

Last Updated: 24/09/2023

Views: 6220

Rating: 4.4 / 5 (65 voted)

Reviews: 88% of readers found this page helpful

Author information

Name: Lidia Grady

Birthday: 1992-01-22

Address: Suite 493 356 Dale Fall, New Wanda, RI 52485

Phone: +29914464387516

Job: Customer Engineer

Hobby: Cryptography, Writing, Dowsing, Stand-up comedy, Calligraphy, Web surfing, Ghost hunting

Introduction: My name is Lidia Grady, I am a thankful, fine, glamorous, lucky, lively, pleasant, shiny person who loves writing and wants to share my knowledge and understanding with you.