Physical Properties of Alkanes: BP Determination and Trends Flashcards

1
Q

What kinds of liquids with have higher boiling points?

A

those with strong intermolecular forces

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2
Q

the point at which the vapor pressure of a chemical is equal to the atmospheric pressure

A

boiling point

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3
Q

Why do molecules with more intermolecular forces have higher boiling points?

A

more kinetic energy is required to break the bonds holding the molecules together

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4
Q

non-polar, single bonded compounds with the general formula Cn H2n+2

A

alkanes

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5
Q

What type of intermolecular forces to alkanes, branched alkanes, and cycloalkanes experience?

A

Van der Waals

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6
Q

What is the boiling point trend for straight chain alkanes?

A

an increase in molecular weight = an increase in BP

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7
Q

Why do branched alkanes have a lower boiling point than both straight chained and cyclo alkanes?

A

Less surface area for intermolecular attraction

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8
Q

General formula for cycloalkanes?

A

CnH2n

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9
Q

Why do cycloalkanes have higher boiling points than their straight chain counterparts?

A

More surface area for intermolecular associations

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10
Q

Trend for boiling points of alkanes?

A

branched alkanes < straight-chain alkanes < cycloalkanes

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11
Q

Why is it important in the boiling point experiment that the thermometer be above the liquid and not in it?

A

We are measuring the temperature of the vapors not the liquid

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12
Q

Steps to determine boiling point of liquid?

A
  1. add sample to small test tube along with boiling chip and clamp onto stirring hot plate
  2. place thermometer about 2 mm above liquid
  3. heat slowly and record data points as function of time
  4. observe the point at which the temperature appears to “level off.” This is the boiling point
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13
Q

Why did we have to use a 360*C thermometer in our experiment?

A

Boiling points of possible compounds exceeded 150*C

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14
Q

Why did we practice with 5 known liquids?

A

To get a grip on the procedure and show that the boiling points may not be spot on but close to the expected value.

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15
Q

Why do alcohols and water have higher boiling points than alkanes?

A

They exhibit hydrogen bonding (stronger intermolecular forces).

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16
Q

What were the 5 knowns in the experiment?

A

pentane, cyclopentane, 2-methylpentane, hexane, and cyclohexane

17
Q

what are the safety hazards of this experiment?

A
  • hot chemicals
  • chemicals have mild odor
  • DO NOT OVERHEAT - slow temp rise is necessary
  • observe temp rise carefully