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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

BOILING POINT

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

vapor pressure equal atmospheric pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q
  • other factors may also affect the boiling point:
A

intermolecular forces of attraction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q
  • the intermolecular forces go in the order
A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q
  • commonly observed among [ “hydrocarbon groups” ] and occurs only within [ “short distances” ] in between molecules
A

Van Der Waals Dispersion Forces

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q
  • occurs among [ “partially ionic or polar molecules” ]
A

Dipole - Dipole Interaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q
  • formed between [ “partially positive
    hydrogen (H+)” ] and an [ “adjacent electronegative atom” ] which bears a partial negative charge
A

Hydrogen Bonding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q
  • intermolecular ______________ tend to “rise boiling point” of an organic compound
A

Hydrogen Bonding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

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

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

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

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

Melting Point

13
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
NMT 0.5 - 1°C
14
* if a compound melts over a "very narrow range", it is assumed that the compound tested is ________________
relatively pure
15
* the presence of "impurities" usually ___________ the melting point and may "increase the melting point range"
depresses
16
estimation of the purity of the substance can be obtained
theoretical melting point value
17
* several factors can also affect melting point:
✓ 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
BOILING POINT = tert-butyl alcohol
82.3 °C
19
BOILING POINT = chloroform
61.2 °C
20
BOILING POINT = n-hexane
68.7 °C
21
BOILING POINT = methanol
64.7 °C
22
MELTING POINT = salicylic acid
211.0 °C
23
MELTING POINT = benzoic acid
122.4 °C
24
MELTING POINT = glucose
146.0 °C
25
MELTING POINT = fructose
103.0 °C
26
* boiling point increase as the number of carbon atoms increase (True or False)
True
27
* boiling point increase in the presence of branching (True or False)
False Correction: * boiling point "decrease" in the presence of branching
28
* boiling point increase as the polarity of the substance increase (True or False)
True
29
* boiling point decrease in the presence of non-volatile impurities (True or False)
False Correction: * boiling point "increase" in the presence of non-volatile impurities
30
* boiling point decrease in the presence of volatile impurities (True or False)
True
31
vapor pressure is qual to?
atmospheric pressure