UCSB CHEM 6AL FINAL REVIEW EXAM
QUESTIONS AND ANSWERS 100% PASS
2026/2027
Intermolecular Forces and how they affect physical properties/purification techniques -
ANS 1. Dipole-Dipole: polar covalent molecules such as aldehydes and ketones. positive and
negative endings. polar molecules must be close together for force to be significant. weaker
than ion-dipole forces. strength increases with the polarity of the molecule.
2. Electrostatic: occurs between charged species, cations, and anions, and is responsible for very
high MP and BP of ionic compounds and metals
3. Hydrogen Bonding: hydrogen atom in a polar bond (NOF). considered a dipole-dipole
interaction; quite polar
4. Ion-dipole: interaction between a charged ion and a polar molecule. cations are attached to
the negative end of the dipole, and anions are attached to the positive end
5. London Dispersion Forces: only types of forces non-polar covalent molecules can experience.
dependent on surface area and polarizability of the surface e of the molecule. results from the
movement of electrons in the molecule, which generate temporary positive and negative
regions in the molecule.
Finding limiting reagents/percent yields/filling out reagent tables - ANS Limiting reagents:
The compound that runs out first in a reaction. When the reagent runs out, reactions can no
longer proceed and another compound is considered in excess. To determine the limiting
reagent, convert the mass to moles using the molar mass of the compound. Then use
stoichiometric ratios to see which is the smaller compound in moles.
Percent Yield: Actual yield/theoretical yield multiplied by 100. If you expect 10g but only get a
yield of 8.4g, the the percent yield is 84%. Get theoretical yield using molar ratio of the limiting
reagent.
2026/2027 ALLRIGHTS RESERVED
1
, Melting Point Ranges- How to measure them - ANS Using a capillary, take a small sample and
heat it up using a melting point range apparatus and observe the solid as it turns into a liquid
and record the given range right before it has fully dissolved.
Melting Point Ranges- How impurities affect melting point range - ANS Solid's have an
ordered crystal lattice structure. Heat makes this structure move enough to the point of
liquidation. The MP represents the amount of energy needed to make the lattice structure
move. Impurities disrupt the crystal structure, making the compound easier to melt. Therefore,
the MP lowers and broadens due to the impurities.
Ideal Liquids/Rault's Law - ANS Ideal Liquid: a liquid that is incompressible (density is
constant), irrotational (no turbulence, flow is smooth), and non-viscous (fluid has no internal
friction). These liquids do not exist in nature and obey Rault's law.
Rault's law: Total pressure can be found by adding up partial pressure. Partial pressure can be
found using this law. To find the mole fraction, divide the moles of compound A by the total
moles of all compounds in the solution.
Simple vs. Fractional Distillation - ANS Simple distillation: Used to purify almost already
purified compounds, used to separate liquid from solid impurities, and removes volatile solvents
from a given solution. There are few cycles. Boiling stones are placed in the liquid. Vapor travels
up and condenses back down in a different tube. This distillation works well when there is a
large difference in boiling points (60-70 degrees C)
Fractional distillation: Fractionating columns increase theoretical plates (where
vaporization/condensation can potentially occur)
Comparison: Fractional distillation results in better separation but a little bit of liquid doesn't
vaporize and total yield decreases due to the need for more cycles during fractionation.
Vapor Pressure/Partial Pressure/Mole Ratios - ANS
Azeotropes - ANS Azeotropes: a mixture of two liquids that has a constant boiling point and
composition throughout distillation. IMF determines differences in boiling points. No longer acts
as an ideal solution. Occurs when the liquid composition is equal to the vapor composition. EX:
water and ethanol
2026/2027 ALLRIGHTS RESERVED
2
QUESTIONS AND ANSWERS 100% PASS
2026/2027
Intermolecular Forces and how they affect physical properties/purification techniques -
ANS 1. Dipole-Dipole: polar covalent molecules such as aldehydes and ketones. positive and
negative endings. polar molecules must be close together for force to be significant. weaker
than ion-dipole forces. strength increases with the polarity of the molecule.
2. Electrostatic: occurs between charged species, cations, and anions, and is responsible for very
high MP and BP of ionic compounds and metals
3. Hydrogen Bonding: hydrogen atom in a polar bond (NOF). considered a dipole-dipole
interaction; quite polar
4. Ion-dipole: interaction between a charged ion and a polar molecule. cations are attached to
the negative end of the dipole, and anions are attached to the positive end
5. London Dispersion Forces: only types of forces non-polar covalent molecules can experience.
dependent on surface area and polarizability of the surface e of the molecule. results from the
movement of electrons in the molecule, which generate temporary positive and negative
regions in the molecule.
Finding limiting reagents/percent yields/filling out reagent tables - ANS Limiting reagents:
The compound that runs out first in a reaction. When the reagent runs out, reactions can no
longer proceed and another compound is considered in excess. To determine the limiting
reagent, convert the mass to moles using the molar mass of the compound. Then use
stoichiometric ratios to see which is the smaller compound in moles.
Percent Yield: Actual yield/theoretical yield multiplied by 100. If you expect 10g but only get a
yield of 8.4g, the the percent yield is 84%. Get theoretical yield using molar ratio of the limiting
reagent.
2026/2027 ALLRIGHTS RESERVED
1
, Melting Point Ranges- How to measure them - ANS Using a capillary, take a small sample and
heat it up using a melting point range apparatus and observe the solid as it turns into a liquid
and record the given range right before it has fully dissolved.
Melting Point Ranges- How impurities affect melting point range - ANS Solid's have an
ordered crystal lattice structure. Heat makes this structure move enough to the point of
liquidation. The MP represents the amount of energy needed to make the lattice structure
move. Impurities disrupt the crystal structure, making the compound easier to melt. Therefore,
the MP lowers and broadens due to the impurities.
Ideal Liquids/Rault's Law - ANS Ideal Liquid: a liquid that is incompressible (density is
constant), irrotational (no turbulence, flow is smooth), and non-viscous (fluid has no internal
friction). These liquids do not exist in nature and obey Rault's law.
Rault's law: Total pressure can be found by adding up partial pressure. Partial pressure can be
found using this law. To find the mole fraction, divide the moles of compound A by the total
moles of all compounds in the solution.
Simple vs. Fractional Distillation - ANS Simple distillation: Used to purify almost already
purified compounds, used to separate liquid from solid impurities, and removes volatile solvents
from a given solution. There are few cycles. Boiling stones are placed in the liquid. Vapor travels
up and condenses back down in a different tube. This distillation works well when there is a
large difference in boiling points (60-70 degrees C)
Fractional distillation: Fractionating columns increase theoretical plates (where
vaporization/condensation can potentially occur)
Comparison: Fractional distillation results in better separation but a little bit of liquid doesn't
vaporize and total yield decreases due to the need for more cycles during fractionation.
Vapor Pressure/Partial Pressure/Mole Ratios - ANS
Azeotropes - ANS Azeotropes: a mixture of two liquids that has a constant boiling point and
composition throughout distillation. IMF determines differences in boiling points. No longer acts
as an ideal solution. Occurs when the liquid composition is equal to the vapor composition. EX:
water and ethanol
2026/2027 ALLRIGHTS RESERVED
2
