Page 1 of 25
2026 UCSB CHEM 6AL FINAL EXAM QUESTIONS WITH
REVISED AND CORRECT ANSWERS GRADED TO PASS.
Intermolecular forces and how they affect physical properties /purification techniques: dipole-
dipole, electrostatic, hydrogen, ion, London,
dipole-dipole: polar covalent molecules such as aldehydes and ketones. positive and negative end.
polar molecules must be close together for force to be significant. weaker than ion-dipole forces;
increase with polarity of molecule.
electrostatic: occur between charged species, cations and anions, and are responsible for very high
MP and BP of ionic compounds and metals
hydrogen bonding: hydrogen atom in a polar bond (NOF). considered a dipole-dipole interaction.
quite polar.
ion-dipole: interaction between a charged ion and a polar molecule. cations are attracted to
negative end of dipole, and anions are attracted to positive end.
London dispersion: dependent on surface area and polarizability of the surface of the molecule.
only types of forces NON-polar covalent molecules can experience. result from the movement of
electrons in the molecule, which generates temporary positive and negative regions in the
molecule.
melting point and melting point range
solid has ordered crystal lattice structure. heat makes this structure move enough to the point where
it becomes a liquid. The melting point is how much energy it takes to make this lattice structre
move. Impurities disrupt the crystal lattice, so impurities make a structure easier to melt. MP also
broadens when a compound is impure. If there is water in the solid, it is impure. solid will stick to
side of capillary if still wet.
Best way to determine MP range if you dont know the MP range:
take a quick measurement to get a rough estimate, then take a second, more careful measurement.
limiting reagents and percent yields
limiting reagents: the compound that runs out first. when limiting reagent runs out, reaction can
no longer proceed and other compound is considered in excess. tell which is limiting reagent by
converting grams or mg used to moles using molar mass. when you have moles, use the
stoichimetric ratios to see which is the smaller amount of moles (mole of reagent under mole
produced of product); this is your limiting reagent. could also compare mole ratios between
reagents to see how much you would need of the other reagent to make reaction go to completion.
use limiting reagent to see how much product we will get.
, Page 2 of 25
percent yield: actual yield/theoretical yield X 100. If you expect 10 g but only get 8.4, your %
yield is 84%. get theoretical yield by taking limiting reagent and seeing how much product can be
made by LR. convert g to mol of LR, then convert mol of LR to mol of product; use molar ratio
for this. then convert the mol of product by multiplying molar mass of product.
distillation: ideal liquids/Raoults law
ideal liquid: a liquid that in incompressible (density is constant), irrotational (no turbulence, flow
is smooth), and nonviscous (fulid has no internal friction). they do not exist in nature. Does not
change composition by mixing. it obeys Raoult's law for all compisitions.
Rauoults Law: shown in picture. total pressure can be found by adding up partial pressure; partial
pressure can be found with Raoult's law.
to find mol fraction (Xa), divide mols of A over total moles of solution.
assumption of raults law:
1) the liquid is ideal
the contribution of each liquid phase can be found by determining the mole fraction of each in the
vapor phase:
(gama)A = PA/Ptotal
Example: what is the partial pressure of EtOH (Po=45 kPa, MW= 46.07 g/mol) if 3.0 g of it is
mixe with 3.0 g of unknown (MW= 32.04)?
18.5
a compound with high IMF will have a ____ BP than a compound with low IMF; Imagine a
solution of water boiling in a round flask. the vapors above this liquid are ______ the liquid
themselves.
higher; the same temp as
T or F: higher vp means that a liquid is harder to turn into a vapor
F its easier!
T or F: molecules with lower IMF exert lower vapor pressures
F they prodcuce higher VPs!
, Page 3 of 25
T or F: compounds with a high vp have a low bp
T :)
How does the vapor composition compare to the liquid composition in a 50:50 mix of two liquids?
if we have pentane and hexane, vapor would not be 50:50, it would be more pentane because
pentane has lower BP.
temperature composition diagram
Lower curve = liquid line
Upper curve = vapor line
can determine the composition of both liquid and gas phases at certain temperatures as well as the
boiling points of certain compositions
Ex: at .8 (point B) decane boiling point is ~100 degrees C and the vapor composition (at point C)
is .5 decane
which substance in the distillation mixture will make up more of the vapor composition
the substance with the weaker intramolecular forces, lower boiling point, and higher vapor pressure
simple vs fractional distillation
simple: used to purify almost already pure compounds, to separate liquid from solid impurities,
and to remove volatile (readily evaporating) solvents. few cycles, heat source to heat liquid. have
boiling stones in liquid. vapors travel up and condense back down into different tube. works well
if there is a large difference in BP (60-70 degrees C). only does one evaporation/ condenstion
cycle). how can we improve this? by using more theoretical plates (each TP represents one
evap/conden cycle). do this by using fractional distillation
fractional distillation: fractionating columns increase Theoretical Plates.
Theoretical plates= surface area where vaporization/ condensation can potential occur
allows for greater separation, very important globally.
2026 UCSB CHEM 6AL FINAL EXAM QUESTIONS WITH
REVISED AND CORRECT ANSWERS GRADED TO PASS.
Intermolecular forces and how they affect physical properties /purification techniques: dipole-
dipole, electrostatic, hydrogen, ion, London,
dipole-dipole: polar covalent molecules such as aldehydes and ketones. positive and negative end.
polar molecules must be close together for force to be significant. weaker than ion-dipole forces;
increase with polarity of molecule.
electrostatic: occur between charged species, cations and anions, and are responsible for very high
MP and BP of ionic compounds and metals
hydrogen bonding: hydrogen atom in a polar bond (NOF). considered a dipole-dipole interaction.
quite polar.
ion-dipole: interaction between a charged ion and a polar molecule. cations are attracted to
negative end of dipole, and anions are attracted to positive end.
London dispersion: dependent on surface area and polarizability of the surface of the molecule.
only types of forces NON-polar covalent molecules can experience. result from the movement of
electrons in the molecule, which generates temporary positive and negative regions in the
molecule.
melting point and melting point range
solid has ordered crystal lattice structure. heat makes this structure move enough to the point where
it becomes a liquid. The melting point is how much energy it takes to make this lattice structre
move. Impurities disrupt the crystal lattice, so impurities make a structure easier to melt. MP also
broadens when a compound is impure. If there is water in the solid, it is impure. solid will stick to
side of capillary if still wet.
Best way to determine MP range if you dont know the MP range:
take a quick measurement to get a rough estimate, then take a second, more careful measurement.
limiting reagents and percent yields
limiting reagents: the compound that runs out first. when limiting reagent runs out, reaction can
no longer proceed and other compound is considered in excess. tell which is limiting reagent by
converting grams or mg used to moles using molar mass. when you have moles, use the
stoichimetric ratios to see which is the smaller amount of moles (mole of reagent under mole
produced of product); this is your limiting reagent. could also compare mole ratios between
reagents to see how much you would need of the other reagent to make reaction go to completion.
use limiting reagent to see how much product we will get.
, Page 2 of 25
percent yield: actual yield/theoretical yield X 100. If you expect 10 g but only get 8.4, your %
yield is 84%. get theoretical yield by taking limiting reagent and seeing how much product can be
made by LR. convert g to mol of LR, then convert mol of LR to mol of product; use molar ratio
for this. then convert the mol of product by multiplying molar mass of product.
distillation: ideal liquids/Raoults law
ideal liquid: a liquid that in incompressible (density is constant), irrotational (no turbulence, flow
is smooth), and nonviscous (fulid has no internal friction). they do not exist in nature. Does not
change composition by mixing. it obeys Raoult's law for all compisitions.
Rauoults Law: shown in picture. total pressure can be found by adding up partial pressure; partial
pressure can be found with Raoult's law.
to find mol fraction (Xa), divide mols of A over total moles of solution.
assumption of raults law:
1) the liquid is ideal
the contribution of each liquid phase can be found by determining the mole fraction of each in the
vapor phase:
(gama)A = PA/Ptotal
Example: what is the partial pressure of EtOH (Po=45 kPa, MW= 46.07 g/mol) if 3.0 g of it is
mixe with 3.0 g of unknown (MW= 32.04)?
18.5
a compound with high IMF will have a ____ BP than a compound with low IMF; Imagine a
solution of water boiling in a round flask. the vapors above this liquid are ______ the liquid
themselves.
higher; the same temp as
T or F: higher vp means that a liquid is harder to turn into a vapor
F its easier!
T or F: molecules with lower IMF exert lower vapor pressures
F they prodcuce higher VPs!
, Page 3 of 25
T or F: compounds with a high vp have a low bp
T :)
How does the vapor composition compare to the liquid composition in a 50:50 mix of two liquids?
if we have pentane and hexane, vapor would not be 50:50, it would be more pentane because
pentane has lower BP.
temperature composition diagram
Lower curve = liquid line
Upper curve = vapor line
can determine the composition of both liquid and gas phases at certain temperatures as well as the
boiling points of certain compositions
Ex: at .8 (point B) decane boiling point is ~100 degrees C and the vapor composition (at point C)
is .5 decane
which substance in the distillation mixture will make up more of the vapor composition
the substance with the weaker intramolecular forces, lower boiling point, and higher vapor pressure
simple vs fractional distillation
simple: used to purify almost already pure compounds, to separate liquid from solid impurities,
and to remove volatile (readily evaporating) solvents. few cycles, heat source to heat liquid. have
boiling stones in liquid. vapors travel up and condense back down into different tube. works well
if there is a large difference in BP (60-70 degrees C). only does one evaporation/ condenstion
cycle). how can we improve this? by using more theoretical plates (each TP represents one
evap/conden cycle). do this by using fractional distillation
fractional distillation: fractionating columns increase Theoretical Plates.
Theoretical plates= surface area where vaporization/ condensation can potential occur
allows for greater separation, very important globally.
