CMY 127
Self-Assessment Exercise 4
Subject:
Reference:
Note:
Pace:
Tutorials:
Exercises:
Theme 4: Intermolecular Forces
Textbook Chapter 12 (12.1 to 12.5) Exercises p. 575 - 580
The answers to the odd-numbered questions are available in Appendix R of the textbook.
You should complete these exercises before 15 August.
The focus during the tutorial sessions which run from 19 August to 29 August will be on this
theme.
2
4
5
7
9
39
43
44
45
52
58
Answers Even-numbered questions:
2.
4.
44.
52.
58.
dispersion; hydrogen bonding; dipole-induced dipole
(a) dispersion (b) hydrogen bonding (c) dipole-dipole (d) dispersion
Polar / non-polar
= –800. J
–753 J
+
2+
2+
K < Na < Ca < Mg
+
Additional Exercises
1. What type of intermolecular forces exist between the units of the following substances (motivate your answers):
[Definitions & theory]
(a) LiF (b) CH4 (c) SO2
2. What type of intermolecular forces exist between the following pairs (motivate your answers):
[Definitions & theory]
(a) HBr and H2S (b) Cℓ2 and Br2 (c) I2 and NO3¯ (d) NH3 and C6H6?
3. Which of the following can form hydrogen bonds with water?
[d]
(a) CH3OCH3 (b) CH4 (c) F¯ (d) HCOOH (e) Na+
4. Which of the following species are capable of hydrogen bonding among themselves?
[c,e]
(a) H2S (b) C6H6 (c) CH3OH (d) HI (e) KF (d) BeH2 (e) CH3COOH
5. Define the term “polarizability”. What kind of molecules tend to have high polarizabilities? What is the relationship between
polarizability and intermolecular forces?
[Definitions and theory]
6. Make labelled molecular structure drawings to explain why ethanol (CH3CH2OH) mixes with water. Draw at least two
ethanol and two water molecules.
[Definitions & theory]
7. Which of the following is likely to be more soluble in hexane, C6H14? Explain your answer.
[benzene]
(a) benzene (C6H6) or glycerol CH2(OH)CH(OH)CH2(OH)
(b) CCℓ4 or CaCℓ2
[CCℓ4]
(c) Octanoic acid CH3(CH2)6COOH, or acetic acid CH3COOH.
[Octanoic acid]
[Octanol]
(d) Methanol CH3OH or Octanol CH3(CH2)7OH
8. Select the substance in each of the following pairs that should have the higher boiling point. Motivate your decision and
identify the types of intermolecular forces in the pure substances.
[Molecular polarity, Definitions & theory]
(a) Ne or Xe
(d) F2 or LiF
(b) CO2 or CS2
(e) NH3 or PH3
(c) CH4 or Cℓ2
9. Diethyl ether has a boiling point of 34.5 , and 1-butanol has a boiling point of 117 :
H
H
C
H
H
O
C
H
C
H H
H
H
C
H
H
H
H
H
C
C
C
C
H
H
H
H
O
H
H
Both of these compounds have the same numbers and types of atoms. Explain the difference in their boiling points.
10. The following compounds have the same number and type of atoms. Which would you expect to have the higher boiling
point?
CH3
CH2
CH2
CH3
CH3 CH
CH3
CH3
11. Under the same conditions of temperature and density, which of the following gases would you expect to behave less ideally:
CH4, SO2? Explain.
[Definitions & theory]
©University of Pretoria
CMY 127
2014