UCSB CHEM 6AL FINAL EXAM
QUESTIONS AND ANSWERS 100% PASS
2026/2027
Intermolecular forces and how they affect physical properties /purification techniques: dipole-
dipole, electrostatic, hydrogen, ion, london, - ANS *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 betwween a charged ion and apolar 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 - ANS 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:
2026/2027 ALLRIGHTS RESERVED
1
,take a quick measurement to get a rough estimate, then take a second, more careful
measurement.
limiting reagents and percent yields - ANS *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 - ANS *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
2026/2027 ALLRIGHTS RESERVED
2
, 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)? - ANS 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. - ANS higher; the same temp as
T or F: higher vp means that a liquid is harder to turn into a vapor - ANS F its easier!
T or F: molecules with lower IMF exert lower vapor pressures - ANS F they prodcuce higher
VPs!
T or F: compounds with a high vp have a low bp - ANS T :)
How does the vapor composition compare to the liquid composition in a 50:50 mix of two
liquids? - ANS 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 - ANS 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
2026/2027 ALLRIGHTS RESERVED
3
QUESTIONS AND ANSWERS 100% PASS
2026/2027
Intermolecular forces and how they affect physical properties /purification techniques: dipole-
dipole, electrostatic, hydrogen, ion, london, - ANS *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 betwween a charged ion and apolar 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 - ANS 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:
2026/2027 ALLRIGHTS RESERVED
1
,take a quick measurement to get a rough estimate, then take a second, more careful
measurement.
limiting reagents and percent yields - ANS *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 - ANS *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
2026/2027 ALLRIGHTS RESERVED
2
, 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)? - ANS 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. - ANS higher; the same temp as
T or F: higher vp means that a liquid is harder to turn into a vapor - ANS F its easier!
T or F: molecules with lower IMF exert lower vapor pressures - ANS F they prodcuce higher
VPs!
T or F: compounds with a high vp have a low bp - ANS T :)
How does the vapor composition compare to the liquid composition in a 50:50 mix of two
liquids? - ANS 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 - ANS 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
2026/2027 ALLRIGHTS RESERVED
3
