UCSB CHEM 6AL Final Review Questions With Correct Answers

UCSB CHEM 6AL Final Review Questions
With Correct Answers


Intermolecular Forces and how they affect physical | | | | | |



|properties/purification techniques - CORRECT ANSWER✔✔-1. Dipole- | | | | |



Dipole: polar covalent molecules such as aldehydes and ketones.
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positive and negative endings. polar molecules must be close together
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for force to be significant. weaker than ion-dipole forces. strength
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increases with the polarity of the molecule.
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2. Electrostatic: occurs between charged species, cations, and anions,
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and is responsible for very high MP and BP of ionic compounds and
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metals
3. Hydrogen Bonding: hydrogen atom in a polar bond (NOF). considered
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a dipole-dipole interaction; quite polar
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4. Ion-dipole: interaction between a charged ion and a polar molecule.
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cations are attached to the negative end of the dipole, and anions are
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attached to the positive end | | | |




5. London Dispersion Forces: only types of forces non-polar covalent
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molecules can experience. dependent on surface area and polarizability
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of the surface e of the molecule. results from the movement of
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electrons in the molecule, which generate temporary positive and
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negative regions in the molecule.
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,Finding limiting reagents/percent yields/filling out reagent tables -
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CORRECT ANSWER✔✔-Limiting reagents: The compound that runs out
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first in a reaction. When the reagent runs out, reactions can no longer
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proceed and another compound is considered in excess. To determine
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the limiting reagent, convert the mass to moles using the molar mass of
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the compound. Then use stoichiometric ratios to see which is the
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smaller compound in moles. | | | |




Percent Yield: Actual yield/theoretical yield multiplied by 100. If you
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expect 10g but only get a yield of 8.4g, the the percent yield is 84%. Get
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theoretical yield using molar ratio of the limiting reagent.
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Melting Point Ranges- How to measure them - CORRECT ANSWER✔✔-
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Using a capillary, take a small sample and heat it up using a melting
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point range apparatus and observe the solid as it turns into a liquid and
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record the given range right before it has fully dissolved.
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Melting Point Ranges- How impurities affect melting point range -
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CORRECT ANSWER✔✔-Solid's have an ordered crystal lattice structure.
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Heat makes this structure move enough to the point of liquidation. The
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MP represents the amount of energy needed to make the lattice
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structure move. Impurities disrupt the crystal structure, making the
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compound easier to melt. Therefore, the MP lowers and broadens due
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to the impurities.
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Ideal Liquids/Rault's Law - CORRECT ANSWER✔✔-Ideal Liquid: a liquid
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that is incompressible (density is constant), irrotational (no turbulence,
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, flow is smooth), and non-viscous (fluid has no internal friction). These
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liquids do not exist in nature and obey Rault's law.
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Rault's law: Total pressure can be found by adding up partial pressure.
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Partial pressure can be found using this law. To find the mole fraction,
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divide the moles of compound A by the total moles of all compounds in
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the solution.
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Simple vs. Fractional Distillation - CORRECT ANSWER✔✔-Simple
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distillation: Used to purify almost already purified compounds, used to
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separate liquid from solid impurities, and removes volatile solvents from
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|a given solution. There are few cycles. Boiling stones are placed in the
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liquid. Vapor travels up and condenses back down in a different tube.
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This distillation works well when there is a large difference in boiling
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points (60-70 degrees C)| | |




Fractional distillation: Fractionating columns increase theoretical plates
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(where vaporization/condensation can potentially occur)
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Comparison: Fractional distillation results in better separation but a
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little bit of liquid doesn't vaporize and total yield decreases due to the
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need for more cycles during fractionation.
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Vapor Pressure/Partial Pressure/Mole Ratios - CORRECT ANSWER✔✔-
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Azeotropes - CORRECT ANSWER✔✔-Azeotropes: a mixture of two
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liquids that has a constant boiling point and composition throughout
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distillation. IMF determines differences in boiling points. No longer acts
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