UKN Practice exam 2

UKN Practice exam 2 - l. (22 pt). Sodium benzoate (see...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 6
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: l. (22 pt). Sodium benzoate (see structure below) is a common food preservative A ‘ former 143A student decided to apply his knowledge to determine how much sodium gm benzoate is present in a can of pineapple preservatives. His plan was to extract the compound into an organic solvent, wash the organic layer with saturated sodiumchloride, evaporate the solveth‘t'afi'd weigh the compound. 0 f we suit Complete the following questions: ‘a. (5 pt.) In order to completely extract the corn und ' organic)- solvent the studegt will need to add NaOI—I/ Nazcotfi. . 7" (CH3)2CO into the {afiueous phaseficircle only one possibility). h. (7 pt.) The reaction thatjvillltake place is: E t - y r 1 whee/a ; est ' l . Q 3+ "hat/l C) c. (5 11131163335 student decided to wash the organic layer with saturated Eodinm chldrid§ solution and@with wateris: sons. have it" SOlellltl‘ES Wt Hi0 _ - 4 WW “Cid/£8 maxim in Genome ctClOiS than Hag U ' PKQVQh‘l’ \l bandth “l0 WY“ Wdfiwe MC" 450%. “(with d. (5 pt.) To make sure that the compound was pure, the student measured its melting point. During the preparation of the sample, the capillary broke and the compound was contaminated wfls particles. Because of this the melting point of the compound will be lowe identical/ higher (circle one ) than the melting point of a reference compound. a Na, 4 ’G /) fly 2. (16 pt.) Mr. Beaker was attempting to synthesis new drug byfiefluxing'xornpounds A and B. He was following the progress of the reaction by taking samples at 2 hours intervals and separating the samples on TLC plate. The following scheme ShOWS the TLC results of the reaction in the beginning, (T=O), afier two hours (T=2) and after 4 hours (T=4). Mr. Beaker concluded that the reaction did not proceed, but his boss concluded that the reaction was completed. (Memos-3% Mao‘ftx/ Explain both conclusions based on the TLC. Your anSWers should explain all observations. l.\ 5 a. The reactiori‘never happened because: “3% WWW WERE hOl” “360‘ up m ‘lha mm b. The reaction was completed becausem SDOT@ 3 WWW SWHQR as hm minim kl @ the end twentian A \Ydltdhh% moi A was the Motion /\0 (“with 3. (13 pt.) A stude {was trying to identify an unknovvn solid compound. He measured the inching point and/“zen dissolved 20 mg of the unknown in @toneT/He used thefsolution _‘ ~ H ___r to carryWo—ufjonestesf'and got a ega we r sult. Then he tested the solution with'2,4—DNP and he observod an orange precipitate. The student concluded that the unknown is a ketone. To his surprise, he got zero for his lab report. a. (5 pt.) What is the chemical composition ofJones reagent? Chit]ch ClCla 1’73?“in Q h. (8 pt.) What was wrong with the student’s conclusion? Provide a short explanation. Since, we, dunes lest was neg peg—could he 3° (1ngth epeghmm Lucas test. Ami a r the ihe as om P or who mam: Cm nldohgjderl ohms em glue tle e + est eta/a all ion/P an. WWW so not/he o Milt/m \ é I, 5. (22 pt.) During his final exam it‘llPébnsflass Harry Potter had to synthesize the -' 3 compound Snagggigjgflo he use isherfiesterifi‘chfimbut he forgo-rt? neutralizethe / A, reaction with sodium carbonate after he—cOmpleTeH‘th'e reflux. ' Answer the following questions: r a. (5 pt.)Why.is the reaction heated to reflux? Use a diagram to support your anSWer. Qcflux \3 +0 hem m a so menus New meow wb 6W Emma“- b. (4 pi.)What is the consequence of not neutralizing the reaction? Why? SEER 806A \DGCK “m OMWMQ om blc. m (wthmmm c. (4 pt.)What will happen if a strong base (Le. NaOH) will be used instead of sodium carbonate? WWW-ta we, hand} neun'otlrze he .5.“ c. (13 pt.) Provide a'detailed reaction mechanism using arrow pushing to explain part b. n 0/2 5. 5:14 01—2 ‘ /21 x *r TL/O \H Ry? p“ CIA/€44 a 11’ C:O_|.\ /O\ 7 R "‘0 Jr 1 \ UT/ R H IE *0 H o 6. (25 pt.) . I. A student was separating two colorless compounds on silica TLC. He was using a TLC plate that didn‘t contain a fluorescent indicator but the compounds absorb UV radiation very strongly. When he looked at the plate under UV light he saw: 'a. White Spots against dark background. I; (D Dar ots a ai twhite background. :2. Nos 3 d. Colorless compounds do not absorb UV light. _ _ I Jute mammal:th II. Liquid C02 is a good solvent for caffeine extraction because: a. It is a polar solvent due to the polarized CO bonds. Cg It is non-polar solvent due to its net dipole moment. E. It is polar solvent due to its high dielectric constant. d. It is non~polar solvent clue to its low ability to act as hydrogen bonds acceptor. a-solu Wt— - III. The Rf of a compogddfiqgti‘tilica gelmii: 0.37 in hexane. Changing theggnhrehp‘to‘a mixture of 1:1 diethylet er/hexane will: (Affirm; a. Decrease the Rf value; . . il- b. Decrease the Rf value by half. r I “i '1“: “ l Increase the Rf value. Q; ’ I 9' i 7 , Double the Rf value , in, IV. Increasing the length of fractionating column will result in: a. Higher chance of forming an azeotrope. la, Increasing the boiling point ofthe distillate. \w' c. Decreasing the number of theoretical plates. @None ofthe above. V. ' g silica gel with smaller particle size in column chromatography will result in: _ ncreasing surface area and therefore improved separation. b‘.""‘lncreasing polarity of the silica and therefore improve separation. 0. Increasing flow rate and therefore getting poor separation. d. None ofthe above (F . - w-uym‘w.a~.......-mw.. 7. (24 pt.) a. Draw the chemical structure of 2,4 DNP: b. Draw a schematic graph that determination of melting point. 9. Draw two chemical structures t hat explain the solubility of phenol solution. d. Which of the following compounds will I (HMLQE—liquid extraction? \' “xxx _ ‘- o ' NH2 0 (CH2)BCH3\_ <\ W J a ooh:3 o in sodium hydroxide q (CfizlscHs COOCH3 a“ W, . \S" @ the formation of emulsions during a“ 05W ...
View Full Document

This note was uploaded on 02/27/2011 for the course CHEM 143A taught by Professor Whitesell during the Spring '08 term at UCSD.

Page1 / 6

UKN Practice exam 2 - l. (22 pt). Sodium benzoate (see...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online