Lab 8

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Apr 3, 2024

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CHEM 282 Experiment #8: Hypochlorite Oxidation of Methyl Ketones by the Haloform Reaction Sophie Wolkoff (20107258) & Kaelen Partridge (20127197) TA: Billy Deng March 27, 2020 Experimental:

The first step of the procedure for this experiment included an introduction to the haloform reaction executed in the lab. This process involved reacting methyl ketones with a halogen in an alkaline medium, forming two products. The products were a haloform, whose components depended on the halogen employed, and a carboxylic acid that was missing one carbon atom from the methyl ketone starting material. Step two was the hypochlorite oxidation of acetophenone which began with mixing 0.6 mL of acetophenone and 23 mL of 5% (w/v) sodium hypochlorite solution in a flask under the fume hood. Once a Liebig condenser was attached to this system, the mixture was stirred with a magnetic stir bar for 30 minutes. Once completed, 0.15 g of sodium sulphite was added to remove the unreacted bleach and the resulting mixture was washed twice with 15 mL of diethyl ether in a separatory funnel. The collected aqueous layer was then acidified by adding 10% hydrochloric acid dropwise, continuing until the reaction appeared as red on neutral litmus paper instead of blue. At this point, a precipitate of benzoic acid was formed which was collected by vacuum filtration, washed with cold water, and then recrystallized from a minimum amount of hot water. The crystals were collected again and air-dried, then their mass, percent yield, and experimental melting point was determined. Step three, which was completed in the interim while the solution from step two was being mixed, involved performing an iodoform test. This test was performed twice in a test tube, first with 3 drops of pure acetone and then with 3 drops of acetophenone. In the test tubes, 10 drops of 10% aqueous potassium hydroxide solution and 3 drops of KI/I solution were added and swirled, and the mixtures were left to stand for 3 minutes. ₂ The test tubes were observed for the formation of a yellow-white precipitate of iodoform,

and the test tubes were then cooled in an ice-water bath if its appearance was not observed. All results and observations were recorded. Results: Table 1: Recrystallized Product Data Mass of Recrystallized Product (g) Percent Yield (%) Experimental Melting Point (°C) Literature Melting Point (°C) for Benzoic Acid 0.097 16.2% 120.0 - 122.2 122 Calculation of the Mass of Recrystallized Product (Mass of watch glass and product (g) - mass of watch glass(g)) = 48.465 g - 48.368 g = 0.097 g Calculation of Percent Yield Balanced reaction: C 6 H 5 COCH 3 + 3 NaOCl + H + ⟶ C 6 H 5 COOH + 2 NaOH + HCCl 3 Moles of acetophenone Moles of C 6 H 5 COCH 3 = Mass of C 6 H 5 COCH 3 / MW of C 6 H 5 COCH 3 = 0.6 g / 120.15 g/mol = 0.005 mol Moles of sodium hypochlorite Moles of NaOCl = Mass of NaOCl / MW of NaOCl = 23 g / 74.44 g/mol = 0.31 mol

Calculate the Limiting Reagent 0.31 mol C 6 H 5 COCH 3 x 1 mol C 6 H 5 COCH 3 / 3 mol NaOCl = 0.015 mol C 6 H 5 COCH 3 To use up all of the sodium NaOCl we would need to use 0.103 moles of C 6 H 5 COCH 3 so therefore C 6 H 5 COCH 3 is the limiting reagent. Moles of C 6 H 5 COOH Moles of C 6 H 5 COOH = 0.005 mol C 6 H 4 (OCH 3 ) 2 x 1 mol C 6 H 5 COOH / 1 mol C 6 H 5 COCH 3 = 0.005 mol of C 6 H 5 COOH Mass of C 6 H 5 COOH Mass of C 6 H 5 COOH = Moles of C 6 H 5 COOH / MW of C 6 H 5 COOH = 0.005 mol x (122.12g/mol) = 0.6 g Percent Yield Percent Yield = [Experimental Mass of C 6 H 5 COOH / Theoretical Mass of C 6 H 5 COOH ] x 100% = [0.097 g / 0.6g] x 100% = 16.2% Table 2: Iodoform Tests with Acetone and Acetophenone Compound used Observations Acetone - Liquid was transparent with a slight yellow tint - Grainy, white precipitate formed at the bottom of the test tube

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