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Organic Chemistry Lab > Module 3: BOILING POINT AND MELTING POINT OF ORGANIC COMPOUNDS > Flashcards

Module 3: BOILING POINT AND MELTING POINT OF ORGANIC COMPOUNDS Flashcards

1
Q

Boiling and Melting Points
* physical properties that can help:

✓__________ unknown compounds
✓functions as an ___________ of substances

A
  1. identify and characterize
  2. index of purity
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2
Q

BOILING POINT

  • the temperature at which the ____________ of the substance is ___________ to the _______________ above it
A

vapor pressure equal atmospheric pressure

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3
Q

BOILING POINT

  • the boiling point of a liquid varies with the atmospheric pressure:
  • it is also an indicator of the volatility of the compound:
A

Note!

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3
Q

BOILING POINT

: a liquid at a higher pressure has a higher boiling point than a liquid at a lower atmospheric pressure (varies)

(True or False)

A

True

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3
Q

BOILING POINT

: the lower the boiling point, the more highly volatile the substance is, and vice versa (volatility)

(True or False)

A

True

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4
Q
  • other factors may also affect the boiling point:
A

intermolecular forces of attraction

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4
Q
  • at a given temperature, a compound will exist as:

✓ “gas” if it has a _________________________
✓ “liquid or solid” if it has _________________

A
  1. low normal boiling point
  2. higher normal boiling point
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5
Q

Intermolecular forces of attraction

  • it occurs between ________________________, “influences” __________ the boiling point and are dependent on the __________________ present on the organic compound
A
  1. one molecule and another
  2. directly
  3. functional groups
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5
Q
  • “weak” intermolecular attraction formed by "induced polarization”\ of molecules which is caused by fluctuating charges due to the nearness of the molecules as they vibrate
A

Van Der Waals Dispersion Forces

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6
Q
  • the intermolecular forces go in the order
A

ionic bonding > hydrogen bonding > dipole-dipole interaction > Van der Waals dispersion forces

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6
Q
  • the functional groups which most easily ionize are “amines and carboxylic acids”, such as the reaction of ammonia (NH3) with a carboxylic acid (carboxylate ion)
A

Ionic Bonding

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6
Q
  • boiling point increases as the number of _______________

✓due to more energy that is required to overcome the increased forces of attraction caused by long carbon chains

A

carbon atoms increase

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6
Q
  • commonly observed among [ “hydrocarbon groups” ] and occurs only within [ “short distances” ] in between molecules
A

Van Der Waals Dispersion Forces

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7
Q
  • these molecules contain an [ “asymmetrical charge” ] due to the two poles of the molecule: one end is partially negative while the other end is partially positive
A

Dipole - Dipole Interaction

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7
Q
  • occurs among [ “partially ionic or polar molecules” ]
A

Dipole - Dipole Interaction

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8
Q
  • formed between [ “partially positive
    hydrogen (H+)” ] and an [ “adjacent electronegative atom” ] which bears a partial negative charge
A

Hydrogen Bonding

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9
Q
  • intermolecular ______________ tend to “rise boiling point” of an organic compound
A

Hydrogen Bonding

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9
Q
  • takes place between molecules having “opposite charges” and involves an “electrostatic interaction” between the two opposite charges
A

Ionic Bonding

10
Q
  • another factor that can affect boiling point is the
A

length of the carbon chain

10
Q
  • boiling point increase in the presence of ________________ impurities

✓due to decrease in the vapour pressure of the liquid

A

non-volatile impurities

10
Q
  • boiling point decrease in the presence of __________

✓it causes the surface area of the molecules to decrease thereby decreasing the forces of attraction between individual molecules

A

branching

11
Q
  • boiling point increase as the polarity of the substance ________________

✓due to the attraction of the positive end of one molecule to the negative end of another molecule

A

increase

12
Q
  • boiling point ____________ in the presence of volatile impurities

✓due to the increase in the vapour pressure of the liquid

A

decrease

13
Q
  • the temperature at which a solid compound is directly converted to its liquid state
A

Melting Point

13
Q

a “pure” crystalline compound has a “sharp melting point” and it completely melts within a narrow range of temperature ____________

! a solid usually melts over a range of temperature

A

NMT 0.5 - 1°C

14
Q
  • if a compound melts over a “very narrow range”, it is assumed that the compound tested is ________________
A

relatively pure

15
Q
  • the presence of “impurities” usually ___________ the melting point and may “increase the melting point range”
A

depresses

16
Q

estimation of the purity of the substance can be obtained

A

theoretical melting point value

17
Q
  • several factors can also affect melting point:
A

✓ difference in the configuration of a compound (eg. isomers)
✓ intermolecular forces of attraction
✓polarity

= (difference in the arrangement of their structures even both are pure)
= (ionic bonding results to higher melting point)
= hydrogen bonding, leads to a higher melting point of compounds

18
Q

BOILING POINT
= tert-butyl alcohol

A

82.3 °C

19
Q

BOILING POINT
= chloroform

A

61.2 °C

20
Q

BOILING POINT
= n-hexane

A

68.7 °C

21
Q

BOILING POINT
= methanol

A

64.7 °C

22
Q

MELTING POINT
= salicylic acid

A

211.0 °C

23
Q

MELTING POINT
= benzoic acid

A

122.4 °C

24
Q

MELTING POINT
= glucose

A

146.0 °C

25
Q

MELTING POINT
= fructose

A

103.0 °C

26
Q
  • boiling point increase as the number of carbon atoms increase

(True or False)

A

True

27
Q
  • boiling point increase in the presence of branching

(True or False)

A

False

Correction:
* boiling point “decrease” in the presence of branching

28
Q
  • boiling point increase as the polarity of the substance increase

(True or False)

A

True

29
Q
  • boiling point decrease in the presence of non-volatile impurities

(True or False)

A

False

Correction:
* boiling point “increase” in the presence of non-volatile impurities

30
Q
  • boiling point decrease in the presence of volatile impurities

(True or False)

A

True

31
Q

vapor pressure is qual to?

A

atmospheric pressure

Organic Chemistry Lab (6 decks)

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