CHEM 232 Lab Final Exam with
Accurate Solutions
Distillation - ANSWER-Essential principle: Understanding boiling point, liquid molecules
are in constant motion, those at surface can escape into the vapor phase, and will
continue to do so until a dynamic equilibrium between liquid molecules escaping and
vapor molecules reentering the liquid phase is established.
Distillation - ANSWER-If temperature rises, molecular motion, # molecules escaping
and equilibrium vapor pressure all increase
Total pressure - ANSWER-The ___ is the sum of the vapor pressure of a liquid and that
of air.
Temperature - ANSWER-When a ____ is reached at which equilibrium vapor pressure
of the sample equals the total pressure, rate of evaporation increases dramatically,
bubbles form and the sample boils.
Simple distillation - ANSWER-Allows separation of components if their boiling points
differ by 40°-50°
Fractional distillation - ANSWER-When a liquid is composed of two volatile components,
#molecules in X,Y in a volume of vapor is proportional to their respective partial vapor
pressures
Liquid - ANSWER-A _____ mixture will have a specific boiling point based on the mole
fraction of each component in the mixture.
Raoult's law - ANSWER-Applying ____, the relative composition of the vapor at a given
temperature, which is dependent on the relative volatility (measured by its boiling point),
can be calculated.
Vapor - ANSWER-The composition of the ___ at that given temperature will be richer int
he more volatile species than the original mixture.
Condenses - ANSWER-If some of that vapor ____, the composition of the condensed
liquid will not be that of the vapor, which will have a boiling temperature lower than that
of the initial vapor.
Distillation - ANSWER-The vapor generated from this new liquid mixture during a
second "____" will now be even richer in the more volatile species.
, Practical considerations - ANSWER-If the lower portion of a distillation column is at a
higher temperature than the top, some condensed vapor will revaporize, even as i flows
down the column to return to the still-pot.
Practical considerations - ANSWER-Ideal temperature differential should be: at the
bottom of the colum: boiling point of the less volatile component; at the top: boiling point
of the more volatile component
Practical considerations - ANSWER-Uncondensed vapor and revaporized samples rise
ever higher in the column and undergo repeated condensations and revaporizations,
becoming richer in the more volatile component with each.
Partition coefficients - ANSWER-____ are dependent on the solubility of the
components in the liquid phase.
Solubility - ANSWER-The ___ of a gas in a liquid decreases as its vapor pressure
increases (which increases with increasing temperature): therefore, more volatile
components pass through column more rapidly and elute first.
Liquid phase - ANSWER-Nature of the interactions with the ___: polar components
most effectively using a polar liquid phase (carbowax 20M)
- Non-polar components separate best with non-polar liquid phase (silicon gum rubber).
How components are detected - ANSWER-Once separated into bands based on boiling
points, components pass through a detector to produce a signal whose voltage is
proportional to the mole fraction of each component in the mobile phase.
FID - ANSWER-The GC's run in our lab use a flame ionization detector (___) to detect
the number of ions produced by the atoms in each component passing the mobile
phase through a hydrogen flame.
How components are detected - ANSWER-Since not all compounds contain the same
number or same type of atoms, they do not all ionize to form the same types or
numbers of ions.
Peak area - ANSWER-As a result, the ___ in a chromatogram, while related to the mole
fraction of each component being analyzed, is not always a direct quantitative measure
of each component unless the components contain the same number of the same
atoms. Rather, one must correct those peak areas so one knows that a given area
reflects a known number of moles each.
Response factors - ANSWER-In the lab, a response factor mixture - one which contains
an equal number of moles of each component-was prepared by determining the volume
Accurate Solutions
Distillation - ANSWER-Essential principle: Understanding boiling point, liquid molecules
are in constant motion, those at surface can escape into the vapor phase, and will
continue to do so until a dynamic equilibrium between liquid molecules escaping and
vapor molecules reentering the liquid phase is established.
Distillation - ANSWER-If temperature rises, molecular motion, # molecules escaping
and equilibrium vapor pressure all increase
Total pressure - ANSWER-The ___ is the sum of the vapor pressure of a liquid and that
of air.
Temperature - ANSWER-When a ____ is reached at which equilibrium vapor pressure
of the sample equals the total pressure, rate of evaporation increases dramatically,
bubbles form and the sample boils.
Simple distillation - ANSWER-Allows separation of components if their boiling points
differ by 40°-50°
Fractional distillation - ANSWER-When a liquid is composed of two volatile components,
#molecules in X,Y in a volume of vapor is proportional to their respective partial vapor
pressures
Liquid - ANSWER-A _____ mixture will have a specific boiling point based on the mole
fraction of each component in the mixture.
Raoult's law - ANSWER-Applying ____, the relative composition of the vapor at a given
temperature, which is dependent on the relative volatility (measured by its boiling point),
can be calculated.
Vapor - ANSWER-The composition of the ___ at that given temperature will be richer int
he more volatile species than the original mixture.
Condenses - ANSWER-If some of that vapor ____, the composition of the condensed
liquid will not be that of the vapor, which will have a boiling temperature lower than that
of the initial vapor.
Distillation - ANSWER-The vapor generated from this new liquid mixture during a
second "____" will now be even richer in the more volatile species.
, Practical considerations - ANSWER-If the lower portion of a distillation column is at a
higher temperature than the top, some condensed vapor will revaporize, even as i flows
down the column to return to the still-pot.
Practical considerations - ANSWER-Ideal temperature differential should be: at the
bottom of the colum: boiling point of the less volatile component; at the top: boiling point
of the more volatile component
Practical considerations - ANSWER-Uncondensed vapor and revaporized samples rise
ever higher in the column and undergo repeated condensations and revaporizations,
becoming richer in the more volatile component with each.
Partition coefficients - ANSWER-____ are dependent on the solubility of the
components in the liquid phase.
Solubility - ANSWER-The ___ of a gas in a liquid decreases as its vapor pressure
increases (which increases with increasing temperature): therefore, more volatile
components pass through column more rapidly and elute first.
Liquid phase - ANSWER-Nature of the interactions with the ___: polar components
most effectively using a polar liquid phase (carbowax 20M)
- Non-polar components separate best with non-polar liquid phase (silicon gum rubber).
How components are detected - ANSWER-Once separated into bands based on boiling
points, components pass through a detector to produce a signal whose voltage is
proportional to the mole fraction of each component in the mobile phase.
FID - ANSWER-The GC's run in our lab use a flame ionization detector (___) to detect
the number of ions produced by the atoms in each component passing the mobile
phase through a hydrogen flame.
How components are detected - ANSWER-Since not all compounds contain the same
number or same type of atoms, they do not all ionize to form the same types or
numbers of ions.
Peak area - ANSWER-As a result, the ___ in a chromatogram, while related to the mole
fraction of each component being analyzed, is not always a direct quantitative measure
of each component unless the components contain the same number of the same
atoms. Rather, one must correct those peak areas so one knows that a given area
reflects a known number of moles each.
Response factors - ANSWER-In the lab, a response factor mixture - one which contains
an equal number of moles of each component-was prepared by determining the volume
