CA2-Ans Key

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Feb 20, 2024

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Start: L f 1. The main principle of separation in the thin-layer chromatography technique is through which of the following? (1 pt.) A. Absorption @ Adsorption . Partition D. Precipitation Consider the structures of fluorene, 9-fluorenone and 9-fluorenonel-carboxylic acid — shown below. Use the diagram and corresponding information to answer questions 2 and 3: » 2 O O 0 (1. 2. Predict which compound is more polar? (1 pt.) C. 3. If a mixture of these three compounds was spotted on a silica TLC plate, which compound would you expect to elute first? (1.5 pts) A 4. After performing a TLC experiment in the lab, a student determines the Rf value of caffein‘e to be 2. The student also notes that the solvent traveled 7.3 cm from the index mark. Based on your knowledge of the TLC technique, what can you conclude about this result? (1.5 pts) A. The spot did not move from the index mark. 9 The Rf result reported by the student does not seem valid. C. The caffeine spot traveled 8cm from the index mark. D. The solvent that the student used for this analysis was non-polar. 5. At 100°C the vapor pressure for water, methanol, and ethanol are 760 torr, 2625 torr and 1694 torr, respectively. Which compound has the highest normal boiling point? (1 pt.) @ Water B. Methanol C. Ethanol Scanned with CamScanner

Match the following terms to their corresponding definitions described in questions 6 to 9. A. Simple distillation C. Ideal solution E. Still-head B. Raoult’slaw D. Dalton’s law temperature 6. The quantitative relationship between vapor pressure and composition of homogeneous liquid mixtures. (1.5 pts) b . . . . N | P 7. Solutions in which the interactions between like molecules are the same as those between unlike molecules. (1.5 pts) . = 8. The temperature of the vapors that reach the thermometer bulb as they progress to the condenser. (1.5 pts) E 9. An equation that describes the relationship between total pressure over a mixture volatile liquid and the partial pressures of each component in the mixture. (1.5 pts) D 10. Which of the following statements about fractional distillation are true? [Select all that are TRUE]. (2 pts) e . (A) Can ideally separate mixtures with comparable volatilities (small BP differences). @ The lower the HETP {height equivalent to a theoretical plate) of the fractionating(packed) i column, the more efficient it is. Can be used to determine the boiling points of components of a mixture of volatile liquids. The distillation process involves several concurrent vaporization-condensation cycles. E. Continual change in boiling temperature is observed as the distillation progresses. 11. For each of the following purifications identify situations where fractional distillation would be more suitable. (2 pts) A. Preparing drinking water from the sea (B) Separating benzene bp 80°C, from toluene, bp 111°C (C) Obtaining gasoline from crude oil D. Removing diethyl ether, bp 35°C, from p-dichlorobenzene mp 175°C - 12. A mixture of 6.3g n-propyl cyclohexane (MW 126.2 g/mol) and 4.0g n-propyl benzene (MW 120.2 g/mol) is distilled, in an open system, through a simple distillation apparatus. The boiling temperature of the first drop of distillate is found to be 157 °C at 760 torr. The equilibrium vapor pressures of n-propyl cyclohexane and n-propyl benzene at 157 °C are 785 torr and 725 torr, respectively. Calculate the percentage of n-propyl benzene in the first drop of distillate. (2 pts) A. 38% C. 58% E. 76% B. 42% D. 62% - Scanned with CamScanner

The figure below describes the temperature-composition relationship of 2-methylpentane (bp 60C) and toluene (bp 110c). 13. Assume that you are provided with an 18 cm fractionating column having an HETP of 6cm to distill a mixture of 30% 2-methylpentane and 70 % toluene (L2). What would be the composition of the first drop of distillate. (2 pts) : A L1 C. L4 E. L6 B. L3 D. L5 - - Pt 0.00 020 040 060 080 1.00 mole % of toluene 14. The main principle of separation in the gas chromatography technique is through which of the following? (1 pt.) A. Absorption B. Adsorption Partition D. Precipitation Scanned with CamScanner

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Match eEaI\ch statement with one of these terms. [questions 15-17] ution Retention factor Retention time Theoretical plate number Chromatogram moonw» 15. The ratio of the amount of analyte in the stationary phase to the amount in the mobile phase. (1.5 pts) B 16. A series of peaks of different sizes provided by components in a mixture. (1.5 pts) E 17. Time it takes after sample injection into the column for the analyte peak to appear as it exits the column. (1.5 pts) C 18. In gas chromatography, the stationary phase is best described as; (1 pt.) A. The interior surface of an untreated capillary column that comes in contact with a liquid _. mobile phase passing through the column @ A thin liquid layer that is chemically bonded to the interior of a capillary column that comes in contact with an inert carrier gas or mobile phase C. Athin layer of silica or alumina particles bound to a two-dimensional plate D. A column packed with solid particles that that come in contact with a liquid mobile phase What would happen to the retention time of a compound if the following changes were made? [questions 19, 20] A. Increase B. Decrease C. No effect 19. Increase the length of the column {1 pt.) A’ 20. Increase the temperature of the column (1 pt.) b End Scanned with CamScanner