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UCSB CHEM 6AL Final Review Questions
and Correct Answers/ Latest Update /
Already Graded
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.
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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.
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,
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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)
All rights reserved © 2025/ 2026 |
UCSB CHEM 6AL Final Review Questions
and Correct Answers/ Latest Update /
Already Graded
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.
All rights reserved © 2025/ 2026 |
, Page |2
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.
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,
All rights reserved © 2025/ 2026 |
, Page |3
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)
All rights reserved © 2025/ 2026 |
