CHEM 233 FINAL EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS) |ALREADY
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In the experiment, you added water to the reaction vessel after the
reaction was complete, but we did not discuss why. Based on what
happened after adding the water, which of the following is the reason for
the addition of water?
a) lower the solubility of the product in solution so it precipitated out
b) increase the solubility of the product in solution so it precipitated out
c) lower the solubility of the product in solution so it stayed in solution
d) increase the solubility of the product in solution so it stayed in
solution Ans✓✓✓a) lower the solubility of the product in solution so it
precipitated out
You recrystallize the product of a bromination reaction by dissolving the
entire product in hot solvent, cooling to room temperature, and then
collecting the solid that crystallized. However, you are disappointed with
your yield. Select all of the following actions that would increase the
amount of solid recovered from the recrystallization.
a) performing a hot filtration
b) cool the recrystallization solution in an ice bath before collecting the
crystals
c) lower the amount of solvent used in the recrystallization while
keeping all impurities dissolved
,e) increase the amount of solvent used in the recrystallization while
keeping all impurities dissolved Ans✓✓✓b) cool the recrystallization
solution in an ice bath before collecting the crystals
c) lower the amount of solvent used in the recrystallization while
keeping all impurities dissolved
Calculate the percent recovery of a recrystallization of a 1.3 g sample of
solid to the tenths place if you recover 0.88 g after the recrystallization.
Round to the nearest tenths. Ans✓✓✓67.7 g.
After performing a recrystallization, you calculate a percent recovery of
110%. Select all possible reasons for this result.
a) The crystals were not dried properly after the recrystallization
b) The recrystallized solid became more dense, increasing its mass
c) Impurities were added to the solid during the recrystallization process
d) Some of the solid melting during the weighing process, increasing its
mass Ans✓✓✓a) The crystals were not dried properly after the
recrystallization
c) Impurities were added to the solid during the recrystallization process
After brominating an alkene, you isolate a solid that is orange in color.
The product is known to be a white solid when pure. What do you
expect the result of performing a melting point analysis on the product to
be?
, a) The melting point will be lower than the melting point of the pure
compound
b) The product will not melt
c) The melting point will be higher than the melting point of the pure
compound Ans✓✓✓a) The melting point will be lower than the melting
point of the pure compound
In an effort to optimize the bromination reaction, you repeat the reaction
three times with each attempt using a slightly different set of reaction
conditions. The melting points of the crude products of each reaction are
shown below. Which reaction produced the most pure crude product ? (2
pts)
Reaction 1: 110 - 114 °C
Reaction 2: 108 - 114 °C
Reaction 3: 113 - 116 °C
a) Reaction 1
b) Reaction 2
c) Reaction 3
d) Impossible to determine Ans✓✓✓c) Reaction 3
DETAILED ANSWERS (VERIFIED ANSWERS) |ALREADY
GRADED A+||BRAND NEW!
In the experiment, you added water to the reaction vessel after the
reaction was complete, but we did not discuss why. Based on what
happened after adding the water, which of the following is the reason for
the addition of water?
a) lower the solubility of the product in solution so it precipitated out
b) increase the solubility of the product in solution so it precipitated out
c) lower the solubility of the product in solution so it stayed in solution
d) increase the solubility of the product in solution so it stayed in
solution Ans✓✓✓a) lower the solubility of the product in solution so it
precipitated out
You recrystallize the product of a bromination reaction by dissolving the
entire product in hot solvent, cooling to room temperature, and then
collecting the solid that crystallized. However, you are disappointed with
your yield. Select all of the following actions that would increase the
amount of solid recovered from the recrystallization.
a) performing a hot filtration
b) cool the recrystallization solution in an ice bath before collecting the
crystals
c) lower the amount of solvent used in the recrystallization while
keeping all impurities dissolved
,e) increase the amount of solvent used in the recrystallization while
keeping all impurities dissolved Ans✓✓✓b) cool the recrystallization
solution in an ice bath before collecting the crystals
c) lower the amount of solvent used in the recrystallization while
keeping all impurities dissolved
Calculate the percent recovery of a recrystallization of a 1.3 g sample of
solid to the tenths place if you recover 0.88 g after the recrystallization.
Round to the nearest tenths. Ans✓✓✓67.7 g.
After performing a recrystallization, you calculate a percent recovery of
110%. Select all possible reasons for this result.
a) The crystals were not dried properly after the recrystallization
b) The recrystallized solid became more dense, increasing its mass
c) Impurities were added to the solid during the recrystallization process
d) Some of the solid melting during the weighing process, increasing its
mass Ans✓✓✓a) The crystals were not dried properly after the
recrystallization
c) Impurities were added to the solid during the recrystallization process
After brominating an alkene, you isolate a solid that is orange in color.
The product is known to be a white solid when pure. What do you
expect the result of performing a melting point analysis on the product to
be?
, a) The melting point will be lower than the melting point of the pure
compound
b) The product will not melt
c) The melting point will be higher than the melting point of the pure
compound Ans✓✓✓a) The melting point will be lower than the melting
point of the pure compound
In an effort to optimize the bromination reaction, you repeat the reaction
three times with each attempt using a slightly different set of reaction
conditions. The melting points of the crude products of each reaction are
shown below. Which reaction produced the most pure crude product ? (2
pts)
Reaction 1: 110 - 114 °C
Reaction 2: 108 - 114 °C
Reaction 3: 113 - 116 °C
a) Reaction 1
b) Reaction 2
c) Reaction 3
d) Impossible to determine Ans✓✓✓c) Reaction 3
