AP Chemistry
Chapter 13 LCD questions
1. Complete the following table:
Substance
Type of
bonding
H2S
CaO
Bromine
Ammonia
Ar
NaI
CO
IMF type
Structure
2. Which will have a higher boiling point: ethanol or dimethyl ether?
Draw the lewis structure, give the shapes and hybridizations for each and
explain why.
What is the relationship between these 2 molecules?
How many Pi and Sigma bonds do they each have?
Write a balanced combustion reaction for each.
3. The chlorofluorocarbon C2Cl3F3 has a normal boiling point of
47.6 °C. The liquid state has a specific heat of 0.91 J/gK and the gas
state has a specific heat of 0.67 J/gK. The enthalpy of vaporization
for this compound is 27.99 kJ/mol. How much heat is exchanged to
heat up 25.00 grams of this compound from 5.0 °C to 82.0 °C?
for rumination: why does it say “normal” boiling point?
How does boiling point change with atm pressure? Why?
How does boiling relate to vapor pressure and IMF?
4. The normal melting and boiling points of xenon are -112 °C
and -107 °C, respectively. Its triple point is at -121 °C and 282
torr and its critical point is at 16.6 °C and 57.6 atm.
a. Sketch the phase diagram for Xe.
b. If Xe gas is cooled under an external pressure of 100 torr,
what will happen? Explain.
5. An element crystallizes in a body centered cubic lattice. The
edge of the unit cell is 2.86 angstroms, and the density of the crystal
is 7.92 g/cm3. Calculate the atomic weight of the element.
Boiling pt
rank
Actual Bp
6. Aluminum metal crystallizes in a face centered cubic cell structure.
If each Al atom has a radius of 1.43 angstroms, what is the length of
a side of the unit cell?
What is the density of aluminum metal?
ANSWERS
Substance
Type of
bonding
IMF type
Structure
H2S
Covalent
Dipole-Dipole
LDF
Individual
molecules;
bent
CaO
Ionic
Crystal lattice
Bromine
Covalent
electrostatic
attraction
LDF
LDF
Ammonia
Covalent
Hydrogen
bonding
LDF
Individual
trigonal
pyramidal
moluecles
Ar
N/A
LDF
Atoms
NaI
Ionic (actually
polar covalent
due to ΔEng =
1.6)
Crystal lattice?
Individual
linear
molecules?
CO
Covalent
some
electrostatic
attraction and
dipole-dipole
LDF
Dipole-Dipole
LDF
Individual
linear
molecules
Individual
linear
molecules
Boiling pt
rank
(predictions)
#4 (note that
bromine is
higher due to
its
considerably
stronger LDF)
Clearly #1
Actual Bp
(°C)
#5 (actually
much higher
due to high
MW and
greater
polarizability)
#3 (note the
fact that it is
not and the
relevance of
LDF in
bromine)
Last (#7)
MW = 39.95
Likely #2 (next
most ionic)
59
#5
Slightly polar
MW = 28
-60
2850
-33
-186
1304
-196
The greater accesibilty to the OH group in ethanol facilitates a much stronger attraction between
molecules than in dimethyl ether, and hence a higher boiling point as well.
Note that in each molecule, all central atoms are sp3 hybridization with the carbons being tetrahedral and
the oxygens being bent.
Each molecule has 8 sigma bonds and no pi bonds.
Each molecule will have the same chemical combustion reaction:
C2H6O + 3O2  2CO2 + 3H2O
3.
82
Temp (°C)
47.6
3
1
2
-5
Time (min)
q1 = msΔT = (25g)(0.921J/gK)(47.6 -5)°C = +969 J
25 g/187.35 g/mol = 0.133 mol
q2 = (0.133 mol)(27.99 x103 J/mol) = +3735 J
q3 = msΔT = (25g)(0.67 J/gK)(82 – 47.6) °C = +576 J
Σ = +5280 J OR 1257 cal
Phase Diagram for Xenon
4.
100 torr = 0.132 atm
The gas will deposit into a solid, crossing the deposition point around-130°C or so (see arrow). The
intermolecular forces will overcome the KE of the molecules, bringing them closer together.