UCSB CHEM 6AL FINAL EXAM 2026 QUESTIONS WITH COMPLETE
SOLUTIONS.
Intermolecular forces and how they affect physical properties /purification techniques: dipole-dipole,
electrostatic, hydrogen, ion, london, - (answer)*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 - (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. 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.
,UCSB CHEM 6AL FINAL EXAM 2026 QUESTIONS WITH COMPLETE
SOLUTIONS.
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. 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.
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)
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
, UCSB CHEM 6AL FINAL EXAM 2026 QUESTIONS WITH COMPLETE
SOLUTIONS.
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 TPs. allows for greater separation, very
important globally.
efficiency: fractional has better separation, but a little bit of liquid doesnt vaporize and yield decreases
due to more cycles needed.
azeotropes - (answer)a mixture of two liquids that has a constant boiling point and composition
throughout distillation. IMF determine differences in BP. no longer acts as an ideal solution. when the
liquid comp=vapor comp. example is water and ethanol.
what is the highest % of alcohol achievable by distillation? - (answer)95-96%. dont drink 200 proof
alcohol (100% EtOH)!!!
chromatography - (answer)Separation of complex mixtures of compounds based on their polarity and
distribution between a solid phase and a mobile phase
what are the (sub)types of chromatography? - (answer)1. Liquid Chromatography (LC): Column
Chromatography and Thin-Layer Chromatography (TLC: A micro version of liquid column
chromatography)
2. High Pressure LC (HPLC)
3. Gas Chromatography (GC)
mobile vs solid phase: definition and how column chromatography works - (answer)*mobile*: Liquid or
gas that carries compounds through
the solid phase. AKA the solvent or the eluent
SOLUTIONS.
Intermolecular forces and how they affect physical properties /purification techniques: dipole-dipole,
electrostatic, hydrogen, ion, london, - (answer)*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 - (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. 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.
,UCSB CHEM 6AL FINAL EXAM 2026 QUESTIONS WITH COMPLETE
SOLUTIONS.
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. 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.
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)
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
, UCSB CHEM 6AL FINAL EXAM 2026 QUESTIONS WITH COMPLETE
SOLUTIONS.
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 TPs. allows for greater separation, very
important globally.
efficiency: fractional has better separation, but a little bit of liquid doesnt vaporize and yield decreases
due to more cycles needed.
azeotropes - (answer)a mixture of two liquids that has a constant boiling point and composition
throughout distillation. IMF determine differences in BP. no longer acts as an ideal solution. when the
liquid comp=vapor comp. example is water and ethanol.
what is the highest % of alcohol achievable by distillation? - (answer)95-96%. dont drink 200 proof
alcohol (100% EtOH)!!!
chromatography - (answer)Separation of complex mixtures of compounds based on their polarity and
distribution between a solid phase and a mobile phase
what are the (sub)types of chromatography? - (answer)1. Liquid Chromatography (LC): Column
Chromatography and Thin-Layer Chromatography (TLC: A micro version of liquid column
chromatography)
2. High Pressure LC (HPLC)
3. Gas Chromatography (GC)
mobile vs solid phase: definition and how column chromatography works - (answer)*mobile*: Liquid or
gas that carries compounds through
the solid phase. AKA the solvent or the eluent
