Download doc CHEM 222 Lab exam with Answers

FACULTY OF SCIENCE
Laboratory Exam
CHEMISTRY 222
LAST NAME
FIRST NAME
STUDENT ID
Version 1
EXAMINER: Prof. D. Harpp & D. Perepichka
DATE: March 26, 2009
ASSOCIATE EXAMINER: Mike Daoust
6:30 - 7:30pm
INSTRUCTIONS:
1. Fill in your name/student number on the answer sheet and on the scantron.
2. Answer all 20 T/F questions (0.5 marks each) as 1 = T and 2 = F
Do not guess. You will lose 0.5 marks for a blank but 0.625 marks for a wrong
answer.
3. Make only a single dark marks (pencil or pen) for your answer. No cross-out of pen marks.
.
INVIGILATORS:
AT THE END OF THE EXAM, PLEASE MAKE A SEPARATE PILE OF THE
COMPUTER ANSWER SHEETS. THANK YOU.
Answer the following True/False questions and indicate T or F.
1. __ F___Recrystallization entails dissolving crystals in a solvent at room
temperature and then allowing them to come back out of solution.
2.__T___ The purpose of refluxing is to carry out a reaction at the boiling point of
the solvent.
3.__F___ All chemical reactions must take place in solution.
4.__T___ When a carbene is formed in the presence of an alkene, a cyclopropane
is obtained via insertion into the double bond.
5.__T___ Carbenes are very reactive towards nucleophiles because of an empty
orbital on the carbene carbon.
6.__F___ An emulsion is essential in the Carbene lab in order to increase the
temperature and thus maximize the yield.
7.__ T__Biphenyl is soluble in ether as well as hexanes.
8.__T___The Grignard reagent will react with any acidic proton such that are
present on carboxylic acids and alcohols.
9._T___ Cyclohexanone, the product of the oxidation lab was purified via a steam
distillation.
10.__T___ Chromic acid, used to convert cyclohexanol to it’s ketone is generated
from sodium dichromate.
11.__F___ Converting an alcohol to a ketone is a reduction.
12.__T___The oxalic acid in the oxidation lab is used to get rid of the excess
oxidizing agent.
13.__F___The yield of the derivative reaction indicates the purity of the initial
product.
14._T___ The Horner-Wadsworth-Emmons reaction (modification of a Wittig)
performed in the lab made use of “instant ylides”. These are solid phase mixtures
of a phosphonium salt with sodium amide. This question was eliminated
15.___ F___A cloudy solution is often wet but a clear solution is always dry.
16.__T___ A low stream of air is often used to evaporate a solvent because it
removes vapors as they form.
17.__F__The aldol condensation reaction proceeds by an SN1 mechanism.
18.__F___In the Aldol condensation reaction performed in the lab, 2 mL of 10%
HCl was added in order to catalyze the Aldol Reaction.
19.__T___ To turn off a rotary evaporator, you must first stop the rotor, open the
system to the atmosphere then turn off the tap to the aspirator and take the round
bottom off.
20.__T___If you wish to dry an organic mixture with both saturated salt solution
(NaCl) and anhydrous sodium sulfate, the salt solution must be removed before
adding sodium sulfate.
2.
Briefly answer the following Questions. Each is worth 1%
21. Why did you add water to the reaction mixture in the work-up of the carbene
reaction?
a) To provide extra hydroxide ions to make carbenes
b) To remove traces of water from the reaction mixture
c) To remove water-soluble sodium hydroxide from the organic layer
d) To stop the reaction
22. In the Grignard Experiment, 10% sulfuric acid was added in the work-up of
the product. What role did it play?
a) To react with the Grignard reagent
b) To protonate triphenylcarbinoloxy magnesium bromide.
c) To destroy the magnesium metal remains.
d) To react with benzophenone.
23. After recrystallization, a MP is taken of the purified crystals. It is found to be
higher than the literature one for that compound. Account for this.
a) the crystals are still wet with solvent
b) the sample contains some impurities
c) the mp determination was taken too fast.
d) all of the above
24. Crossed Aldol condensations:
a) are useful if one of the aldehydes (or ketones) has no hydrogens.
b) involve attack of an enolate of one compound on the carbonyl group of a
second compound.
c) are successful when one of the two carbonyl compounds is more
susceptible to nucleophilic attack
d) all of the above
25. Silica gel beads are used in the esterification experiment because
a) they act like boiling chips.
b) silica helps to stabilize the reaction
c) their use drives the reaction to the right
d) none of the above