Lab Report

Chemistry professor Dave MacInnes cites these particular virtues of the following lab report:

  • An excellent introduction: short and to the point
  • A well-organized Procedure section which clearly states the steps employed
  • Effective use of the table in the Results section, with easy-to-read data
  • A clearly stated Conclusion which relates well to the Introduction and shows good understanding of the lab's purpose
  • Nice use of the various features of Word.
  • Overall: good references, all sections of the report covered well, good drawing.

Dave describes the lab report as "excellent."

The Beauty of Salicylic Acid

Introduction

Organic chemistry has played a huge role in our society as the manipulation of some compounds can form all different types of useful materials including, soaps, antiseptics, medicines, and scented oils. The purpose of this experiment is to show some of the uses of one organic compound, salicylic acid. The lab manual says that this substance which was isolated in 1838 comes from the salicin in the white willow bark. Salicin was used in early times as a cure for Rheumatism. Its medical uses include antiseptics, fever reducers, and astringents. The salicylic acid compound formed from the salicin can be synthesized further to form acetylsalicylic acid or more commonly known as aspirin. This compound was first synthesized in 1853 but not until 1897 did anyone take it to a manufacturing corporation. Then the Bayer Corporation began to market the product as a pain reliever and antipyretic. Billion dollars of aspirin are sold each year and it can be found in most households across the world (Chemical Principles II Lab Manual 15-16). In this lab the aspirin will be formed and then tests will be done to examine the success of this formation. A separate use of salicylic acid will be shown as the lab will form a liquid compound, methyl salicylate. This compound is used in fragrances such as wintergreen. An additional experiment will be conducted which extracts caffeine from tea. This shows the process that is used to isolate a single substance from a natural source. It is similar to the process used to extract salicin from the white willow. The tea and the caffeine are just easier to obtain than a white willow. Overall the lab focuses on showing methods of how to obtain organic compounds as well as the many uses and formations that one substance can form.

Procedure: The Formation of Acetylsalicylic Acid

Materials:

250mL Erlenmeyer flask

100mL Beaker

Two 800mL Beaker

Small and large graduated cylinders

Vacuum filtration setup

Stirring rod

Watch glass

Hot plate

Dropper

Chemicals: source the 1996-1997 Aldrich Catalogue

Salicylic acid: 99+% purity, HOC6H4CO2H, It has a free weight of 138.12, melting point of 158-160° and a boiling point of 211° /22mm, it is a toxic irritant.

Acetic anhydride: 99+% purity, (CH3CO)2O, FW 102.09, a melting point of --73° , a boiling point of 138-140° , and a density of 1.082. It is toxic and when reacting with water it produces heat.

Sulfuric acid: 95-98% purified, H2SO4 (A.C.S.). It is a strong acid.

Ethanol: It has a boiling point of 78.5° and a melting point of --114.1° , and a density of 785. It is highly toxic and flammable.

Procedure:

Place the 800mL beaker with about 400mL of water on the hotplate. Make sure that the setup is close to the hood. The setup will serve as a hot bath for the 250mL flask.

Put 4g of salicylic acid in the 250mL flask and add 16mL of acetic anhydride under the hood. During this make sure that the opening of the flask is pointed away from everything.

Add 10 drops of Sulfuric acid to act as a catalyst for the reaction. After adding the acid swirl the mixture. Once again keep the opening pointed away from everything.

Put the 250mL flask in the hot water bath and heat for 10 mL.

After ten minutes is up remove the flask from the water and let it cool to room temperature. To speed up the process place the outside of the flask under tap water.

While the substance is cooling setup an ice bath using an 800mL beaker filled halfway with ice and water.

Slowly add 50mL of ice cold water to the 250mL in small intervals.

Place the flask in the ice bath and let it completely crystallize.

Setup the vacuum filtration and filter the liquid from the crystals. After the crystals are dry mass the product.

After a week, the substance needs to be recrystallized. Do this by dissolving the substance in a minimum amount of hot ethanol in a 250mL beaker. (Heat ethanol on the hot plate and add it slowly with a dropper. While adding it keep the 250mL beaker over the hot plate but not touching the hot plate).

Add 5-10mL of distilled water and place it in an ice bath to crystallize completely.

Use the vacuum filtration setup and let the crystals dry over night.

Results:

Data from Part A:

Acetylsalicylic Acid (Aspirin)

 

Theoretical yield and Properties (data taken from pure acetylsalicylic acid)

Actual Yield and Properties (data taken from our sample)
Mass

5.22g

2.26g
Melting point

135° C

111° C
Testing for Unreacted Salicylic acid (Using FeCl3 as an indicator, dark means presence of salicylic acid):

Light purple

Darker deeper purple

The products of the synthesis were small, white, flaky crystals. In the formation of acetylsalicylic acid there was a 43.3% yield. The actual product differed in the melting point by 24° C. In the qualitative analysis the results were similar to the results of the salicylic acid indicating a presence of unreacted salicylic acid.

Discussion and Conclusions:

We were successful in forming acetylsalicylic acid (aspirin). The results showed that our sample was not quite as pure as it could have been. The tests that were conducted to determine the purity of the acetylsalicylic acid proved that the sample was not that pure. The melting point test was twenty four degrees lower than that of pure acetylsalicylic acid indicating that either the bonds were not the same or their was other substances mixed in. When testing for excess salicylic acid the test came up deep purple when compared to the pure acetylsalicylic acid's light purple results it showed that there was an excess amount of unreacted salicylic acid. In the formation of the acetylsalicylic acid there was 43.3% yield. The percent yield might have been caused by a loss of crystals in transferring the substance from the filter paper to the watch glass. Our product took longer to crystallize which gave us better-shaped crystals but might not have completely crystallized causing a shortage of actual yield. In order to create purer acetylsalicylic acid, more acetic anhydride could be added to the reaction. This would ensure that all of the salicylic acid reacted and that it was the limiting reactant. The unreacted acetic anhydride can be destroyed when ice cold water is added. After the acetic anhydride is destroyed a purer solution of acetylsalicylic acid should be formed.

References

Anne Glenn, Dave MacInnes, and Rob Whitnell, Chemical Principles II Lab Manual (Greensboro: Guilford College, 1998).

Richard Morris, et al., Aldrich Catalogue 1996-1997 (Milwaukee: Aldrich Chemical Catalogue, 1996).

Amy Eiwen and Tyler Long, Lab 1

--Jenny Akman

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