NAME:_________________________
Spring 2008
INSTRUCTIONS:
1.
(a)
(b)
(c)
(d)
or
(e)
or
or
2.
(a)
(b)
Section:_____
Student Number:________________
Chemistry 1000 Midterm #2A - Answers
____/ 56 marks
1) Please read over the test carefully before beginning. You should have 6
pages of questions, a blank page that can be used if you run out of space
on any question, and a data/formula/periodic table sheet.
2) If you use the “overflow” page, indicate this next to the question and
clearly number your work on the “overflow” page.
3) If your work is not legible, it will be given a mark of zero.
4) Marks will be deducted for incorrect information added to an otherwise
correct answer.
5) Marks will be deducted for improper use of significant figures and for
missing or incorrect units.
6) Show your work for all calculations. Answers without supporting
calculations will not be given full credit.
7) You may use a calculator.
8) You have 90 minutes to complete this test.
Write a balanced chemical equation for the reactions of the following compounds with
neutral water. Include states of matter. No reaction is a valid answer.
[5 marks]
Cesium
[1 mark]
2Cs(s) + 2H2O(l) → 2CsOH(aq) + H2(g)
Lithium oxide
[1 mark]
Li2O(s) + H2O(l) → 2 LiOH(aq)
Aluminium
[1 mark]
no reaction (initial formation of Al2O3 passivation layer).
Sodium chloride
[1 marks]
NaCl(s) + H2O(l) → NaCl(aq) + H2O(l)
→ NaCl(aq)
NaCl(s)
Barium
[1 marks]
Ba(s) + 2 H2O(l) → Ba(OH)2(s) + H2(g)
Ba(s) + 2 H2O(l) → Ba(OH)2(aq) + H2(g)
Ba(s) + 2 H2O(l) → Ba2+(aq) + 2 OH-(aq) + H2(g)
Specify the charges of the ions present in the following ionic compounds and write their
formulae.
[4 marks]
potassium superoxide
K+ O2- ions or 1+ and 1KO2
barium nitride
Ba2+ N3- ions or 2+ and 3Ba3N2
NAME:_________________________
3.
Section:_____
Student Number:________________
A unit cell of a rhenium oxide is shown in the picture below.
grey atoms: Re
[5 marks]
white atoms: O
(a)
Describe the lattice type of the rhenium atoms
simple cubic packing of Re
(b)
How many rhenium atoms and how many oxygen atoms are inside one unit cell? [2 marks]
8(1/8) = 1 rhenium atom
12(1/4) = 3 oxygen atoms
(c)
What is formula for this rhenium oxide?
ReO3
4.
You are given two shiny, silvery pieces of metals. You are told that one is strontium and the
other is aluminium, and are asked to tell which is which. How can this be done? Make sure
you clarify how you’ll know which metal is which.
[3 marks]
Reaction with water.
Sr reacts with water.
Al does not react with water (only initially to form the passivation layer).
[2 marks]
[1 mark]
NAME:_________________________
Section:_____
Student Number:________________
5.
Predict the structures of magnesium oxide and magnesium sulfide. Describe the two
structures with respect to anion packing and cations filling holes.
[6 marks]
+ MgO: r /r = 72/121 = 0.595
NaCl structure
2fcc of O with all octahedral holes filled with Mg2+
MgS: r+/r- = 72/184 = 0.391
ZnS structure
2fcc of S with half of the tetrahedral holes filled with Mg2+
6.
Give an example of chemical similarities of lithium and magnesium. What are these
similarities referred to?
[2 marks]
Any one of the following:
• form normal oxides (Li2O, MgO)
• form nitrides (Li3N, Mg3N2)
• hard metals
• carbonates decomposes to oxides and CO2 when heated
Diagonal relationship
7.
What are the electrolysis products in the industrial production of aluminium? (Specify the
states of matter)
[2 marks]
liquid Al
gaseous CO2.
8.
Write down the reaction involved in the production of potassium. Explain briefly why this
reaction is different from the one to make sodium.
[5 marks]
KCl is reduced by Na:
KCl (l) + Na (l) → NaCl (l) + K (g)
K is distilled off to shift the equilibrium to the right side.
The electrolysis of molten KCl is not viable since K is soluble in KCl and the separation
would be difficult.
NAME:_________________________
Section:_____
Student Number:________________
At ambient pressure of 1 atm, calcium carbonate (CaCO3) releases CO2 at 900 °C. Calculate
the volume of carbon dioxide gas that can be obtained by heating 32.6 g of calcium
[7 marks]
carbonate to 1000 °C (1273.15 K) and 101 kPa.
3
Give your answer both in L and in m
9.
CaCO3(s)
→
CaO(s) +
CO2(g)
M(CaCO3) = 100.087 g/mol
nCaCO3 =
32.6 g
= 0.326mol
100.087 g / mol
nCO2 = nCaCO3 = 0.326mol
PV = nRT
⎛
V=
nRT
=
P
⎞
(0.326mol )⎜⎜ 8.3145 Pa ⋅ m ⎟⎟(1273.15 K )
V = 0.0341m 3 ×
⎝
3
mol ⋅ K ⎠
101kPa
1000 L
= 34.1L
1m 3
×
1kPa
= 0.0341m 3
1000 Pa
NAME:_________________________
Section:_____
Student Number:________________
10.
Diffraction experiments showed that iron (Fe) crystallizes in a body-centered cubic cell at
room temperature (α-Fe). The metallic radius is 124.1 pm.
[9 marks]
(a)
Calculate the density of α-iron (in g/cm3).
[7 marks]
ρ = m/V
Mass in one unit cell:
One unit cell contains 2 iron atoms:
g ⎞⎛
1mol
⎞
⎛
− 22
mcell = 2 M Fe = 2atoms ⎜ 55.847
⎟ = 1.8547 × 10 g
⎟⎜
23
mol
6
.
02214
10
atoms
×
⎠
⎠⎝
⎝
*1.8547×10-25 kg is also acceptable (comes from using atomic mass units→kg conversion)
To find the volume of the unit cell, find the cell length (a) and relate that to the radius since
a = √(16/3) r. (atoms touch through the body diagonal)
a = 286.6 pm × (102cm /1012 pm) = 286.6 × 10-10 cm = 2.866 × 10-8 cm
V = (2.866 × 10-8 cm)3 = 2.354 × 10-23 cm3
−22
⎛ m ⎞ 1.8547 × 10 g
=
= 7.879 gcm −3
⎟
− 23
3
⎝ V ⎠ 2.354 × 10 cm
ρ =⎜
(b)
At 906 °C iron converts into a modification with fcc packing. Do you expect a piece of iron
to contract or expand when heated from room temperature to 1000 °C?
[1 mark]
contract
(c)
Iron in fcc packed modification can contain carbon. The carbon atoms are located in some of
the octahedral holes of the iron packing. What is the limiting stoichiometry/formula when all
octahedral holes are filled with carbon atoms? (in reality, carbon contents is much smaller
than the limiting one)
[1 mark]
1:1 stoichiometry: FeC
NAME:_________________________
Section:_____
Student Number:________________
11.
(a)
[8 marks]
Sketch a Born-Haber cycle for lithium oxide.
2Li+
(g)
2I1
+
O2-(g)
[4 marks]
∆lfH
Li2O(s)
∆EA(2)H
O-(g)
2 Li(g)
∆EA(1)H
∆fH
O(g)
2∆sublH
2 Li(s)
(b)
1/2∆BDH
+ 1/2 O2
Using information from the data sheet, calculate the enthalpy of lattice formation of lithium
oxide.
[4 marks]
∆ f H ° Li2O = 2∆ subl H Li + 2 I 1, Li + 12 ∆ BD H O −O + ∆ EA (1) H O + ∆ EA( 2 ) H O + ∆ LF H Li2O
[
∆ LF H Li2O = ∆ f H ° Li2O − 2∆ subl H Li + 2 I 1, Li + 12 ∆ BD H O −O + ∆ EA(1) H O + ∆ EA ( 2 ) H O
]
kJ ⎞ ⎡⎛
kJ ⎞ ⎛
kJ ⎞ ⎛ 1
kJ ⎞ ⎛
kJ ⎞ ⎛
kJ ⎞⎤
⎛
∆ LF H CdCl 2 = ⎜ − 597.9
⎟ − ⎢⎜ 2 × 159.4
⎟ + ⎜ 2 × 520.2
⎟ + ⎜ 2 × 498
⎟ + ⎜ − 142
⎟ + ⎜ 844
⎟
mol ⎠ ⎣⎝
mol ⎠ ⎝
mol ⎠ ⎝
mol ⎠ ⎝
mol ⎠ ⎝
mol ⎠⎥⎦
⎝
kJ
∆ LF H CdCl 2 = −2908
mol
NAME:_________________________
Section:_____
Student Number:________________
Some Useful Constants and Formulae
Fundamental Constants and Conversion Factors
Atomic mass unit (u)
1.6605 × 10-27 kg
Avogadro's number
6.02214 × 1023 mol–1
Bohr radius (a0)
5.29177 × 10-11 m
Electron charge (e)
1.6022 × 10-19 C
Electron mass
5.4688 × 10-4 u
Ideal gas constant (R)
8.3145 J·mol-1·K-1
8.3145 m3·Pa·mol-1·K-1
Formulae
c = λυ
E = hυ
rn = a0
n2
Z
λ=
p = mv
E n = − RH
Z2
n2
Ek =
6.626 × 10-34 J·Hz-1
1.0072765 u
1.0086649 u
2.179 x 10-18 J
2.9979 x 108 m·s-1
1 bar = 100 kPa
Planck's constant
Proton mass
Neutron mass
Rydberg Constant (RH)
Speed of light in vacuum
Standard atmospheric
pressure
1 2
mv
2
h
p
∆x ⋅ ∆p >
h
4π
PV = nRT
Data
Radius
(pm)
59
72
184
121
Ion
Li+
Mg2+
S2O2-
Radius
(pm)
77
72
69
67
Ion
Re4+
Re5+
Re6+
Re7+
Li(g)
Li2O(s)
∆fH˚
(kJ·mol-1)
159.4
-597.9
O(g)
249.2
Species
Radius Ratio, r+/r0.225-0.414
0.225-0.414
Structure
Zinc blende, ZnS
Wurtzite, ZnS
1
Further Data for
Lithium
I1 = 520.2 kJ·mol-1
I2 = 7298.1kJ·mol-1
∆EAH = -59.6 kJ·mol-1
∆sublH = 159.4 kJ·mol-1
Further Data for
Oxgyen
I1 = 1251.1 kJ·mol-1
∆EA1H = -142 kJ·mol-1
∆EA2H = 844 kJ·mol-1
∆BDHO=O = 498 kJ·mol-1
Structure Radius Ratio, r+/rNaCl
0.414-0.732
CsCl
0.732-1.00
CHEM 1000 Standard Periodic Table
18
4.0026
1.0079
H
He
1
2
2
13
14
15
16
17
6.941
9.0122
10.811
12.011
14.0067
15.9994
18.9984
Li
Be
B
C
N
O
F
Ne
3
22.9898
4
24.3050
5
26.9815
6
28.0855
7
30.9738
8
32.066
9
35.4527
10
39.948
20.1797
Na
Mg
11
39.0983
12
40.078
3
4
5
6
7
8
9
10
11
12
44.9559
47.88
50.9415
51.9961
54.9380
55.847
58.9332
58.693
63.546
65.39
K
Ca
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
19
85.4678
20
87.62
21
88.9059
22
91.224
23
92.9064
24
95.94
26
101.07
27
102.906
28
106.42
29
107.868
30
112.411
31
114.82
32
118.710
33
121.757
34
127.60
35
126.905
36
131.29
Rb
Sr
37
132.905
38
137.327
Cs
Ba
55
(223)
56
226.025
Fr
87
Ra
Y
39
La-Lu
Ac-Lr
88
P
S
Cl
Ar
15
74.9216
16
78.96
17
79.904
18
83.80
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
41
180.948
42
183.85
43
186.207
44
190.2
45
192.22
46
195.08
47
196.967
48
200.59
49
204.383
50
207.19
51
208.980
52
(210)
53
(210)
54
(222)
Hf
Ta
W
Re
Os
Ir
Pt
Au
72
(261)
73
(262)
74
(263)
75
(262)
76
(265)
77
(266)
78
(281)
79
(283)
Rf
Db
Sg
105
106
138.906
140.115
140.908
144.24
La
Ce
Pr
Nd
57
227.028
58
232.038
59
231.036
60
238.029
Ac
Si
14
72.61
40
178.49
104
89
25
(98)
Al
13
69.723
Th
90
Pa
91
U
92
Bh
107
Hs
Mt
Dt
Hg
Tl
Pb
Bi
Po
At
80
81
82
83
84
85
174.967
Rg
108
109
110
111
(145)
150.36
151.965
157.25
158.925
162.50
164.930
167.26
168.934
173.04
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
61
237.048
62
(240)
63
(243)
64
(247)
65
(247)
66
(251)
67
(252)
68
(257)
69
(258)
70
(259)
71
(260)
Np
93
Pu
94
Am
95
Cm
96
Rn
86
Bk
97
Cf
98
Es
99
Fm
100
Md
101
No
102
Lr
103
Developed by Prof. R. T. Boeré