O-007C Pre-lab_ CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I_II

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10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 1/9 O-007C Pre-lab Due No due date Points 18 Questions 15 Available Sep 5 at 12a.m. - Dec 6 at 11:59p.m. Time Limit 30 Minutes Allowed Attempts 2 Instructions Attempt History Attempt Time Score KEPT Attempt 2 10 minutes 18 out of 18 LATEST Attempt 2 10 minutes 18 out of 18 Attempt 1 26 minutes 16 out of 18 Correct answers are hidden. Score for this attempt: 18 out of 18 Submitted Oct 24 at 4:25a.m. This attempt took 10 minutes. Provide the correct answer to each of the following questions. 1 / 1 pts Question 1 Match the laboratoy equipment or glassware with their correct name. a.
10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 2/9 Reflux condenser b. Stir plate c. Round bottom flask d. Lab jack e. Three prong clamp 1 / 1 pts Question 2 Answer 1: TLC, which stands for Thin Layer Chromatography , is an easy and fast method to visualize different compounds in a liquid mixture. Like many separation techniques in organic chemistry, TLC uses the differences in polarity between compounds for separation. The separation is based on how the compounds in a mixture interact with the silica or alumina of the stationary phase and the solvent used as mobile phase. When the thin layer is made of silica, nonpolar substances will travel further up the plate as the solvent moves up the plate, compared to polar substances, which will travel a smaller distance. Chromatography
10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 3/9 Answer 2: Answer 3: Answer 4: Answer 5: Answer 6: Answer 7: polarity stationary mobile nonpolar solvent polar 1 / 1 pts Question 3 Any organic compound can be visualized on a TLC plate when the plate is placed under UV light. True False This is correct! Only the organic compounds that contain conjugated double bonds in their structure will be visible under the UV light.
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10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 4/9 This is correct! Only the organic compounds that contain conjugated double bonds in their structure will be visible under the UV light. 1 / 1 pts Question 4 The stain used as a secondary visualization method is ammonium molybdate. What is the chemical formula of this compound? NH MoO 4 2 (NH ) MoO 4 4 2 (NH ) Mo 4 4 (NH ) MoO 4 2 4 2 / 2 pts Question 5 A graduate students want to do a large scale Fischer esterification of 6 g of 2-chloro-4-nitrobenzoic acid. What amount of anhydrous ethanol should they use for the reaction, considering the concentration of the acid is the same as the concentration used in experiment O-007C of the 3rd-year labs? Give your answer in milliliters (mL) and rounded to the nearest integer. 99
10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 5/9 1 / 1 pts Question 6 The reaction progress can be monitored using thin-layer chromatography. Which compound would you predict will have the larger R value? f Both compounds will have the same R f It cannot be determined with the provided information. 4-nitrobenzoic acid ethyl 4-nitrobenzoate 2 / 2 pts Question 7 What are the reasons for the brine wash of the organic layer? To remove as much water as possible from the organic layer (trapped droplets) before using a drying agent. To optimize neutralize any base/acid left. To decrease the boiling point of the product. To break any emulsion that might have formed between the organic layer and the aqueous layer. To promote the recrystalization of the sample in the following step. 2 / 2 pts Question 8
10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 6/9 What is/are the role(s) of ethanol in the Fischer esterification reaction you will perform? Catalyst Nucleophile Electrohpile Solvent Acid 1 / 1 pts Question 9 Which of these can help speed up the crystallization process? Scratching the bottom of the flask with a glass rod All of the above Increasing the concentration of the solution Cooling down the solution
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10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 7/9 1 / 1 pts Question 10 What is the role of concentrated sulfuric acid in this reaction? It protects the nitro group from the nucleophilic attack by ethanol It protonates the carbonyl group rendering it more electrophilic It protonates ethanol rendering it more nucleophilic It is a co-solvent 1 / 1 pts Question 11 Why is it important to use anhydrous ethanol in this experiment? Water can slow down the reaction Water can hydrolyze the ester product back to the starting acid Water would reduce the solubility of the starting material in ethanol A higher temperature is required to achieve reflux if water is present 1 / 1 pts Question 12 Why is a large excess of ethanol used in this reaction? Because some ethanol will be consumed by sulfuric acid
10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 8/9 Because ethanol acts as a base as well as anucleophile Because the solubility of 4-nitrobenzoic acid in ethanol is very low Because it helps shift the equilibrium towards the desired product 1 / 1 pts Question 13 Carboxylic acids do not typically react with alcohols in the absence of a Bronsted or Lewis acid. Why is this? Because carboxylic acids are too acidic Because carboxylic acids are poor electrophiles Because alcohols are poor nucleophiles Because alcohols are too basic 1 / 1 pts Question 14 An alternative way to convert a carboxylic acid into its ethyl ester consists in reacting it with... ...ethylmagnesium bromide ...a base and ethyl iodide ...diazomethane ...an alkene and a base
10/24/23, 4:25 AM O-007C Pre-lab: CHEM 3XX ALL LABS 2023W1 Chemistry Integrated Laboratory I/II https://canvas.ubc.ca/courses/122851/quizzes/652127 9/9 1 / 1 pts Question 15 What distinctive change would you expect in the IR spectrum of the ester product compared to the starting carboxylic acid? The appearance of a new signal around 1600 cm -1 The appearance of a new broad signal around 3000 cm -1 The disappearance of a broad signal around 3000 cm -1 The disappearance of a signal around 1800 cm -1 Quiz Score: 18 out of 18
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