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Experiment 10: Synthesis of Benzoic Acid Jasmine Castro General Chemistry 1110-07 Feb 7, 2020

Purpose: The purpose of this experiment is to carry out the synthesis of benzoic acid by the oxidation process and to purify the benzoic acid by the process of recrystallization. Theory and Principles: Oxidation is a chemical reaction that involves the movement of electrons. During oxidation there is a loss of electrons and gaining of oxygen. Oxidation is often associated with the process that occurs at the same time, essentially doing the opposite which is called, reduction. Reduction is the gaining of electrons and the loss of oxygen. These two processes form what is called redox. While there is an exchange of oxygen in some cases oxygen doesn’t need to be present for a redox reaction to occur. Benzaldehyde can be oxidized by potassium permanganate. The given equation for this reaction is: MnO−4 +2H2 O → MnO2 + 4OH − The reduction process is done with the addition of 3 electrons. In the experiment, we will be using ethanol, the KMnO4 will convert to MnO2. This allows for the process to be carried out efficiently. Both the oxidation and reduction equations can be added together to form the net equation of the entire chemical process. C6 H5 CHO+ 3OH − → C6 H5 COO− +2H2 O+2e− +

MnO4− +2H2 O + 3e− → MnO2 + 4OH −

Since the number of electrons would not cancel out when added, multiplying each reaction by a number will have the electrons canceling out. (C6 H5 CHO+ 3OH − → C6 H5 COO− +2H2 O+2e− ) x3 +

(MnO−4 +2H2 O + 3e− → MnO2 + 4OH − ) x 2

3C6 H5 CHO+2MnO4− +OH− → 3C6 H5 COO− +2MnO2  + 2H2 O

This chemical equation is the net reaction. Once this chemical process is complete a sample of benzoic acid is produced. This process is not always done as anticipated or as written and may need to be purified to make sure that the sample is pure benzoic acid. This is done by the process of recrystallization. Recrystallization is a technique that is used to purify a chemical. In this experiment, benzoic acid will be recrystallized. This is done by dissolving the chemical along with its impurities in an appropriate solvent. The solvent will either dissolve the chemical or the impurity. The most commonly used solvent is water at room temperature. Benzoic acid is found to be more soluble in hotter water than colder. This shows that ideal solvent for benzoic acid is hot water which will dissolve the impurities and the solution will be cooled to crystallize. Which is where the name for the process recrystallization comes from. Once the benzoic acid is recrystallized the percent yield can be found. The equation for percent yield is: % yield =

observed mass of product maximum possible mass of product

x 100%

(eq.1)

By using the amount of benzaldehyde put into the reaction, the amount of expected benzoic acid can be found. This number is then used to divide by the amount of benzoic acid that was actually produced. Experimental Procedures: The procedure used is cited below. Harold Goldwhite; Wayne Tikkanean; Vicki Kubo-Anderson; Errol Mathias. Density and Composition of Solutions. Experiments in General Chemistry, 5th edition; Macmillan Learning Curriculum Solutions; Plymouth, 2018; 63-67.

Data Tables/Summary: Table 1. Recorded mass of graduated cylinder w/ and w/o benzaldehyde. Recorded mass of benzoic acid collected Mass of 10mL graduated cylinder +

32.1g

benzaldehyde (g) Mass of 10mL graduated cylinder after

26.77g

transfer(g) Mass of recrystallized benzoic acid +

89.0g

container(g) Mass of container used for benzoic acid(g)

85.23g

Results: Sample Calculations: Equation 1: Calculating how much Benzaldehyde that was put into reaction. 1. 32.1g-26.77g= 5.33g 𝐶8 H𝑂2 Finding Theoretical Yield: 2. 5.33 𝑔 𝑜𝑓 𝐵𝑒𝑛𝑧𝑎𝑙𝑑𝑒ℎ𝑦𝑑𝑒 𝑥 𝑎𝑐𝑡𝑢𝑎𝑙 𝑦𝑖𝑒𝑙𝑑

3. % yield: 𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑦𝑖𝑒𝑙𝑑=

1 𝑚𝑜𝑙𝑒 𝐶8 𝐻8 𝑂2

3.77𝑔 5.95𝑔

136.16𝑔

𝑥 152.112𝑔 𝐶8 𝐻8 𝑂3 = 5.95g

= 63%

Discussion: 1a. Unlike Sodium Benzoate, benzoic acid is less soluble in water because of the polarity of benzoic acid. Water is polar, which attracts other polar molecules. The carboxylic acid group in benzoic acid is polar but the rest of the molecule is non-polar. Also, there are no internal stabilizing structures that favor carboxylate.

iron/K2 O

2a. N2 (g) + 2H2 (g) →

2NH3 (g)

100 Mg → 0.1 g ammonia 0.1 g ammonia x

2 mole H2 1 mole ammonia 2.01588 g x x 17.03052 g 2 mole ammonia 1 mole H2

=0.012 grams of H2 0.90 percent yield =

xg = 0.90 x 0.012 g of H2 0.012 g of H2

=0.11 g of H2 observed 3a. There was a dramatic shift color which leads to believe that there were an abundant number of chemical species. I believe that the organic compounds are responsible for the color change because of the color shift. Conclusion: In conclusion, we observed that benzoic acid is a lot more soluble in hot water than it is in cold water because temperature helps speed the reaction. In addition, the experiment was done successfully. The benzoic acid was effectively synthesized because it was able to dissolve in water at room temperature and the addition of HCl helped precipitate benzoic acid. However, the final product was not the best solution because the percent yield of the solution was 63% and this means the product was not completely pure. The maximum possible mass of the product was 5.95 grams, which was higher than the percent yield; therefore the final product is not entirely pure. References: Harold Goldwhite; Wayne Tikkanean; Vicki Kubo-Anderson; Errol Mathias. Density and Composition of Solutions. Experiments in General Chemistry, 5th edition; Macmillan Learning Curriculum Solutions; Plymouth, 2018; 63-67.

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