Exp. 11 Lab Report PDF

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Lab Report Experiment 11. Synthesis of Benzoic Acid ...

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2/7/2018 Experiment 11. Synthesis of Benzoic Acid

Purpose: The purpose of this experiment is to prepare benzoic acid through oxidation. Then our benzoic acid will be recrystallized and eventually will be analyzed by a pH titration with standard NaOH in a later experiment. Theory/Principles: Benzaldehyde under a mild oxidizing condition in a basic solution oxidizes the –CHO group to – CO2 while the rest of the molecule remains unchanged. In this experiment potassium permanganate is used to oxidize benzaldehyde giving the reaction of C6H5CHO + MnO^- 4 + OH-  C6H5COO- + MnO2 + H2O. In order to create neutral benzoic acid then an a strong acid (ethanol) is added to our solution giving the reaction of C6H5COO- (aq) + H+ (aq)  C6H5COOH. Since benzoic acid is soluble in water at room temperature then we must add HCl to precipitate it until solution is acid. However, recrystallization will occur when benzoic acid is dissolved in hot water and the solution is cooled. Through recrystallization benzoic acid is purified. Leaving the final product over for the next lab period will completely dry our product in which we will weigh it in order to obtain the % yield of benzoic acid based on our collected mass of benzaldehyde we used. To obtain the % yield we are given the equation of: observed mass of product/ maximum possible mass of product x 100%. Experimental Procedures: -

No changes done to lab experiment procedure except for the procedure lasting 3 labs due to having to leave our recrystallized product to fully dry in order to gain its mass

Goldwhite, H.; Tikkanen, W. Experiment 11.Synthesis of Benzoic Acid, Experiments in General Chemistry, 4th ed.;The McGraw Hill Companies. (78-79) Data Tables/Summary:

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Data #1: Signed pre-lab including my data collected on the notebook throughout the experiment

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Data # 2: Formatted version of my data collected from the lab experiment including extra calculated data such as mass of recrystallized benzoic acid & calculated % yield of benzoic acid

Results and Discussion:

Sample Calculations: -

Calculating Mass of benzaldehyde= (mass of cylinder + benzaldehyde – mass of cylinder + benzaldehyde after transfer): (30.0g-24.8 g)= 5.2 g

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Calculating Mass of recrystallized benzoic acid= (mass of recrystallized benzoic acid + watch glass – mass of watch glass): (56.8 g- 53.81 g)= 2.99 g

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Calculating Theoretical Mass of Benzoic Acid: Mass of C7H6O (Benzaldehyde) = 106.12 g/mol # Moles of benzaldehyde used= 5.2 g Benza. X 1 mol. / 106.12 g/mol = 0.04900 moles 1:1 ratio 0.04900 moles x 1 mol. of benzoic acid/ 1 mol. of benzaldehyde= 0.04900 moles Mass of C7H6O2 (Benzoic Acid) = 122.12 g/mol 0.04900 moles x 122.12 g/ mol. = 5.98 g of benzoic acid

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Calculating % yield of Benzoic acid: % yield= (2.99 g / 5.98 g) x 100 %= 50 % yield of benzoic acid

Logical Explanation: By going through the process of synthesizing benzoic acid I was able to obtain the necessary data needed for determining my % yield of benzoic acid and creating a recrystallized product that I would eventually need for a later experiment. In order to reach to my final calculation of 50% yield of benzoic acid I needed the specific data of 10 mL grad. cylinder + benzaldehyde and the mass of 10 mL grad. cylinder + benzaldehyde after transferring it into my solution of KMnO4/NaOH in order to obtain my mass of benzaldehyde used in grams which I would eventually use for finding the number of moles of benzaldehyde by dividing my grams of

benzaldehyde used by the overall mass of C7H6O (benza.). To find the maximum possible mass of my recrystallized product I must multiply the moles of benzaldehyde to the neutral formation mass of benzoic acid (C7H6O2) which occurred when the addition of a strong acid (ethanol) was added into my solution. Thus, the reaction of C6H5COO- (aq) + H+ (aq) C6H5COOH (C7H6O2) gives a 1:1 ratio. Lastly, I needed the data of my recrystallized benzoic acid + watch glass and mass of watch glass used to store/ carry my benzoic acid to find the weight of my observed product. To obtain a recrystallized benzoic acid, HCl is added to my solution for it to precipitate it, until my solution is acid because benzoic acid and sodium benzoate are water soluble due to hydrogen bonding with water. From here the benzoic acid is to be dissolved in hot water and solution cooled for recrystallization to occur. Finally, with this data collected I just plug in my mass of observed of product (2.99 g)/ maximum possible mass of product (5.98 g) x 100% to get my 50% yield of benzoic acid. Discussion Questions: 1. As mentioned before benzoic acid is less soluble than sodium benzoate is in water because sodium benzoate has an ionic interaction with water while benzoic acid forms hydrogen bonds with water. Since ionic compounds are more soluble in water compared to neutral compounds such as benzoic acid it then makes it less soluble than sodium benzoate in water. 2. N2 + 3H2  2NH3 6g of 3H2 & 34 g of 2NH3 100 Mg of ammonia 100 x 10^6 g H2 required: 6 g x (100x 10^6 g)/ 34 g = 1.76 x 10^7 g

90 % yield ammonia: 1.76 x 10^7 g x 100/90 = 1.96 x 10^7 g 1 ton= 907185 g Tons of H2 required: 1.96 x 10^7 g/ 907185 = 21.60 tons 3. During the oxidation of benzaldehyde with KMnO4/NaOH I saw color changes from initially purple to turning dirty brown due to MnO2 forming as the reaction progresses. By adding the remaining portions of KMnO4 to the solution the color purple of KMnO4 will eventually fade to it just being a really dark brown color. Thus, making the inorganic compounds KMnO4/NaOH and MnO2 responsible for the colors observed in the experiment. Conclusion: Through the preparation of benzoic acid through oxidation in order to obtain a purified recrystallized product and collect the data necessary along the way I was able to find my % yield of benzoic acid of 50% at the end of the experiment. References: Goldwhite, H.; Tikkanen, W. Experiment 11.Synthesis of Benzoic Acid, Experiments in General Chemistry, 4th ed.;The McGraw Hill Companies. (77-79)...