UCSB CHEM 6AL FINAL 2026 STUDY
GUIDE COMPREHENSIVE
QUESTIONS ANSWERS VERIFIED A+
◉ melting point and melting point range
Answer: 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
Answer: *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.
,*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
Answer: *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)?
Answer: 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.
Answer: higher; the same temp as
◉ T or F: higher vp means that a liquid is harder to turn into a vapor
Answer: F its easier!
◉ T or F: molecules with lower IMF exert lower vapor pressures
Answer: F they prodcuce higher VPs!
◉ T or F: compounds with a high vp have a low bp
Answer: T :)
◉ How does the vapor composition compare to the liquid composition
in a 50:50 mix of two liquids?
Answer: 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
Answer: 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
Answer: the substance with the weaker intramolecular forces, lower
boiling point, and higher vapor pressure
◉ simple vs fractional distillation
Answer: *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
GUIDE COMPREHENSIVE
QUESTIONS ANSWERS VERIFIED A+
◉ melting point and melting point range
Answer: 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
Answer: *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.
,*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
Answer: *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)?
Answer: 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.
Answer: higher; the same temp as
◉ T or F: higher vp means that a liquid is harder to turn into a vapor
Answer: F its easier!
◉ T or F: molecules with lower IMF exert lower vapor pressures
Answer: F they prodcuce higher VPs!
◉ T or F: compounds with a high vp have a low bp
Answer: T :)
◉ How does the vapor composition compare to the liquid composition
in a 50:50 mix of two liquids?
Answer: 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
Answer: 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
Answer: the substance with the weaker intramolecular forces, lower
boiling point, and higher vapor pressure
◉ simple vs fractional distillation
Answer: *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
