CHEM 233 Unit 4 Exam Questions With
Correct Answers
What type of distillation will you perform first? (1 pt) - ANSWER fractional
distillation
A fractional distillation involves the use of a fractionating column to provide
multiple condensation/evaporation cycles over a given distance. (1 pt) -
ANSWER true
A fractional distillation is less efficient (less capable of giving pure product) than
a simple distillation. (1 pt) - ANSWER false
The distillate you collect from your final simple distillation should have a head
temperature (temperature at the thermocouple) of 80 °C to 85 °C. What does this
temperature correspond to? (1 pt) - ANSWER roughly the boiling point of your
desired alkene product
For the Bayer test, you will add a solution of potassium permanganate to which
of the following items? Select all that apply. (1 pt) - ANSWER a solution of your
isolated product
a solution of your starting alcohol
You consider starting material A. You know that A can undergo two reactions as
shown in the below reaction coordinate diagram with one reaction pathway
labeled in red and one reaction pathway labeled in blue. The red path leads to
Product B, while the blue path leads to Product C. Assuming both reaction
pathways occur simultaneously in competition with each other, what is the
major product, and why? (2 pts) - ANSWER Product B, because the transition
state leading to Product B is lower in energy than the transition state leading to
Product C.
Let's push a little further. We did not discuss this in the webcast, but imagine you
have a multi-step reaction, whose reaction coordinate diagram is shown below.
Using what you know about transition state energies, which step is the rate-
determining step? (1 pt) - ANSWER B to C
Which of the following nucleophiles would perform well as a nucleophile, but
poorly as a base? (1 pts) - ANSWER chloride ion
, The alkyl halide shown below undergoes an elimination reaction. Select all
possible elimation products from the given structures provided below. (1 pts) -
ANSWER A (Hofmann product)
You are performing an elimination reaction using an alkyl halide and a non-bulky
base. The three products shown below are produced in the reaction. What
product would be created in the smallest amount? (2 pts) - ANSWER A
(Hofmann/terminal alkene)
You know the Bayer test is used to identify the presence of alkenes. You attempt
to perform an elimination reaction and test what you hope is the product using
the Bayer test. Adding KMnO4 to a solution of the starting material requires 2
drops to remain purple, with no precipitate observed. A solution of your
potential product requires 15 drops to remain purple, with no precitipate
observed. Did you successfully perform an elimination reaction? (1 pts) -
ANSWER Yes, because the solution of potential product took more drops of
KMnO 4 to remain purple.
A mixture of 0.9 mole fraction B is distilled by fractional distillation using a
Vigreux column having two theoretical plates. (Keep in mind that the initial
boiling of mixture in the distillation flask before the column adds an
additional"plate".) According to the phase diagram below, what is the
composition of the distillate (liquid from condensed vapor) you collect? Select
the answer closest to the expected value. (2 pts) - ANSWER 0.30 mole fraction B
The below phase diagram corresponds to what type of mixture? (1 pts) -
ANSWER non-ideal solution with a negative deviation
If a liquid mixture containing 60 Mole Percent B was distilled using a simple
distillation, according to the below phase diagram, what temperature would the
liquid mixture boil at? (2 pts) - ANSWER 68 degrees C
If a liquid mixture containing 60 Mole Percent B was distilled using an efficient
fractional distillation column, according to the below phase diagram, what
temperature would be read on the thermometer at the top of the fractionating
column? Think back to what you observed in the Elimination experiment! (1 pts)
An "efficient" fractional distillation column is efficient when it has at least the
required number of theoretical plates to distill a mixture to a desired purity.
Assume that the fractional distillation column can do as many distillations as you
could need or has an infinite number of theoretical plates. - ANSWER 50 degrees
C
If a liquid mixture containing 80 mole percent B were distilled using an efficient
fractional distillation column, what would be the composition of the liquid
remaining in the distillation pot? (2 pts) - ANSWER 75 mole percent B
Correct Answers
What type of distillation will you perform first? (1 pt) - ANSWER fractional
distillation
A fractional distillation involves the use of a fractionating column to provide
multiple condensation/evaporation cycles over a given distance. (1 pt) -
ANSWER true
A fractional distillation is less efficient (less capable of giving pure product) than
a simple distillation. (1 pt) - ANSWER false
The distillate you collect from your final simple distillation should have a head
temperature (temperature at the thermocouple) of 80 °C to 85 °C. What does this
temperature correspond to? (1 pt) - ANSWER roughly the boiling point of your
desired alkene product
For the Bayer test, you will add a solution of potassium permanganate to which
of the following items? Select all that apply. (1 pt) - ANSWER a solution of your
isolated product
a solution of your starting alcohol
You consider starting material A. You know that A can undergo two reactions as
shown in the below reaction coordinate diagram with one reaction pathway
labeled in red and one reaction pathway labeled in blue. The red path leads to
Product B, while the blue path leads to Product C. Assuming both reaction
pathways occur simultaneously in competition with each other, what is the
major product, and why? (2 pts) - ANSWER Product B, because the transition
state leading to Product B is lower in energy than the transition state leading to
Product C.
Let's push a little further. We did not discuss this in the webcast, but imagine you
have a multi-step reaction, whose reaction coordinate diagram is shown below.
Using what you know about transition state energies, which step is the rate-
determining step? (1 pt) - ANSWER B to C
Which of the following nucleophiles would perform well as a nucleophile, but
poorly as a base? (1 pts) - ANSWER chloride ion
, The alkyl halide shown below undergoes an elimination reaction. Select all
possible elimation products from the given structures provided below. (1 pts) -
ANSWER A (Hofmann product)
You are performing an elimination reaction using an alkyl halide and a non-bulky
base. The three products shown below are produced in the reaction. What
product would be created in the smallest amount? (2 pts) - ANSWER A
(Hofmann/terminal alkene)
You know the Bayer test is used to identify the presence of alkenes. You attempt
to perform an elimination reaction and test what you hope is the product using
the Bayer test. Adding KMnO4 to a solution of the starting material requires 2
drops to remain purple, with no precipitate observed. A solution of your
potential product requires 15 drops to remain purple, with no precitipate
observed. Did you successfully perform an elimination reaction? (1 pts) -
ANSWER Yes, because the solution of potential product took more drops of
KMnO 4 to remain purple.
A mixture of 0.9 mole fraction B is distilled by fractional distillation using a
Vigreux column having two theoretical plates. (Keep in mind that the initial
boiling of mixture in the distillation flask before the column adds an
additional"plate".) According to the phase diagram below, what is the
composition of the distillate (liquid from condensed vapor) you collect? Select
the answer closest to the expected value. (2 pts) - ANSWER 0.30 mole fraction B
The below phase diagram corresponds to what type of mixture? (1 pts) -
ANSWER non-ideal solution with a negative deviation
If a liquid mixture containing 60 Mole Percent B was distilled using a simple
distillation, according to the below phase diagram, what temperature would the
liquid mixture boil at? (2 pts) - ANSWER 68 degrees C
If a liquid mixture containing 60 Mole Percent B was distilled using an efficient
fractional distillation column, according to the below phase diagram, what
temperature would be read on the thermometer at the top of the fractionating
column? Think back to what you observed in the Elimination experiment! (1 pts)
An "efficient" fractional distillation column is efficient when it has at least the
required number of theoretical plates to distill a mixture to a desired purity.
Assume that the fractional distillation column can do as many distillations as you
could need or has an infinite number of theoretical plates. - ANSWER 50 degrees
C
If a liquid mixture containing 80 mole percent B were distilled using an efficient
fractional distillation column, what would be the composition of the liquid
remaining in the distillation pot? (2 pts) - ANSWER 75 mole percent B
