3. A pure white crystalline compound was found to melt at 112.5-113.0°C when taken on amelting point apparatus, and on further heating, the liquid was found to turn brown at ca.145-150 °C. The capillary containing the melted compound was set aside to cool, andresolidify. When the sample was retried, using the same capillary the sample melted at133.6-154.5°C. Why is the melting point higher than 112°, and the range so wide?4. When performing a melting point on a solid compound using a melting point apparatus, twomelting point determinations were made. One sample, which was 1 mm in height in thecapillary, possessed a melting point of 200.0-200.5°C. The other sample was 25 mm inheight. What would you expect the approximate melting point to be for this sample,assuming identical heating rates of 1°/min? (Hint: heat is applied from the bottom of thesample) (Give an actual numerical approximation!)

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Macroscale and Microscale Organic Experiments

7th Edition

ISBN:9781305577190

Author:Kenneth L. Williamson, Katherine M. Masters

Publisher:Kenneth L. Williamson, Katherine M. Masters

Chapter5: Distillation

Section: Chapter Questions

Problem 2Q

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Which of the following could DECREASE the amount of the recovered crystals in the purification by recrystallization experiment? Collecting the recrystallized benzoic acid by filtration using a pre-weighed filter paper. Using a long-stemmed funnel in the hot filtration step. Cooling the filtered solution rapidly. Washing the recovered crystals using hot solvent. a. II, III b. II, IV c. II, III, IV d. I, II, III, IV
A student recrystallized some impure benzoic acid and isolated it by filtration. He scraped the purified benzoic acid off the filter paper after it had dried and took the melting point as a test for purity. He was surprised that most of the white solid melted sharply between 121 and 122 °C but that a small amount remained unmelted even at temperatures above 200 °C. Explain this behavior.
1. Why is the washing of crystals on the filter paper not as effective a process of purification as crystallization?2. How do you account for the formation of crystals of different sizes in slow and rapid crystallization process?3. What properties should ideally be possessed by a recrystallization solvent?
A student recrystallized some impure benzoic acid and isolated it by filtration. He scraped the purified benzoic acid off the filter paper after it had dried and took the melting point as a test for purity. He was surprised that most of the white solid melted sharply between 121 and 122 0C but that a small amount remained unmelted even at temperatures above 200 0C. Explain this behavior.
What effect does the presence of impurity have on the melting point? Can the amount of impurity be quantified by melting point determination?
What will be the composition of the vapor when a mixture containing 0.30 of A was subjected to fractional distillation with two theoretical plates? a 0.72 A; 0.28 B b 0.87 A; 0.13 B c 0.50 A; 0.50 B d 0.30 A; 0.70 B
6.0 mL of cyclohexanol, 8 mL of 85% phosphoric acid, and 10 drops of sulfuric acid are added to a 50-mL round-bottom flask with boiling chips, and the mixture is distilled into an ice-cooled receiver. The distillate is in the form of a colorless bi-phasic mixture. The cyclohexene upper layer is removed from the water layer, and dried over anhydrous calcium chloride. Isolated is cyclohexene as a clear and colorless foul-smelling liquid. Weighing data is given below. Gross mass: 51.24 g Tare mass: 48.04 g Product mass: 3.2g Question: Calculate the theoretical mass of the cyclohexene product, bearing in mind that the cyclohexanol starting material was measured by volume, not by mass (so you must use the density of cyclohexanol to convert milliliters to grams, before calculating the number of moles). Calculate the percent yield of cyclohexene obtained.
What is the main drawback of using steam distillation in the isolation of volatile oils from its matrix?
Explain melting point determination as a characterization technique.
why does the observed meltin point change over the course of distillation
0.56 g 1,4‐dimethoxybenzene, 0.9 mL 2‐chloro‐2‐methylpropane, 5 mL nitrobenzene and 0.52 g graphite were combined, and the mixture was refluxed for 1.5 hours. It was then cooled to room temperature and filtered. The filtered graphite was washed with 15 mL hexane. The filtrate was distilled under vacuum to remove any remaining 1,4‐dimethoxybenzene, 2‐chloro‐2‐ methylpropane and nitrobenzene (6.3 g), yielding 0.44 g 1,4‐di‐tert‐butyl‐2,5‐dimethoxybenzene (43.4% yield). What is the Atom economy, E factor, and effective mass yield?
In a chromatographic analysis, a solution containing 0.0837M toluene and 0.0666M xylene resulted in peak areas of Atoluene= 423 and Axylene= 347. To analyze an unknown sample, 10.0mL of 0.146M xylene was added to 10.0mL of an unknown toluene-containing solution, and the mixture was diluted to 25.0mL. This mixture gave a chromatogram with peak areas of Atoluene= 553 and Axylene= 582. What was the concentration of toluene in the unknown solution?

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A pure white crystalline compound was found to melt at 112.5 C when taken on a melting point annaratus and on further heating he liguid was found to turn brown at ca