NAME:_________________________
Spring 2012
INSTRUCTIONS:
Section:_____
Student Number:________________
Chemistry 1000 Midterm #2A
____/ 65 marks
1) Please read over the test carefully before beginning. You should have 6
pages of questions and a double-sided formula/periodic table sheet.
2) If your work is not legible, it will be given a mark of zero.
3) Marks will be deducted for incorrect information added to an otherwise
correct answer.
4) Marks will be deducted for improper use of significant figures and for
missing or incorrect units.
5) Show your work for all calculations. Answers without supporting
calculations will not be given full credit.
6) You may use a calculator.
7) You have 90 minutes to complete this test.
Confidentiality Agreement:
I agree not to discuss (or in any other way divulge) the contents of this exam until it has been
marked and returned. I understand that breaking this agreement would constitute academic
misconduct, a serious offense with serious consequences. The minimum punishment would be a
mark of 0/65 on this exam and removal of the “overwrite midterm mark with final exam mark”
option for my grade in this course; the maximum punishment would include expulsion from this
university.
Signature: ___________________________
Course: CHEM 1000 (General Chemistry I)
Semester: Spring 2012
The University of Lethbridge
Date: _____________________________
Question Breakdown
Q1
Q2
Q3
Q4
Q5
Q6
Q7
Q8
Q9
Q10
/11
/2
/4
/4
/8
/8
/6
/6
/10
/6
Total
/65
NAME:_________________________
Section:_____
Student Number:________________
1.
Answer the following questions by filling in the blanks.
(a)
Beryllium has similar properties to what Group 13 metal? ______Aluminum__________.
(b)
The correct name for NiCl2 is __nickel (II) chloride__________________.
(c)
The alkaline earth metal that produces salts giving green flame tests is ___Barium_______.
(d)
Iron(III) sulfide has the molecular formula ___Fe2S3_________________.
(e)
Calcium carbide has the molecular formula _____Ca2C_______________.
(f)
An atom which has octahedral electron group geometry (1 lone pair + the appropriate
number of bonding atoms) has ___square pyramidal_____________ molecular geometry.
(g)
A cubic lattice is _____less____________ dense than a face-centered cubic lattice.
(h)
NaCl crystallizes in a face-centered cubic lattice. In which type of holes are the cations
found in? ________octahedral________________.
(i)
What
other
type
of
hole
is
found
in
[11 marks]
a
face-centered
cubic
lattice?
___tetrahedral___________.
(j)
Give an example of a metal whose oxide exhibits amphoteric properties. ____Al or Be___.
(k)
Give the symbol of the least reactive alkaline earth metal ________Beryllium__________.
2.
Explain why a block of aluminium does not react with water.
[2 marks]
Under normal circumstances, aluminium metal is coated with a thin layer of aluminium
oxide (Al2O3). This oxide layer protects the bulk aluminium metal from reacting with
anything that does not first react with the Al2O3. Al2O3 does not react with water.
NAME:_________________________
Section:_____
Student Number:________________
3.
For the following questions, you can assume that you have access to any
materials/equipment you’ve used in the Chemistry 1000 lab. Your answer may not violate
any safety regulations!
[4 marks]
(a)
You’re given two vials, each containing a white salt. You’re told that one vial contains
sodium carbonate (Na2CO3) and the other contains magnesium carbonate (MgCO3). How
do you determine which salt is which? Briefly, explain how your method will tell you which
is which.
Method A: Add each salt to a beaker containing water. The Na2CO3 will dissolve while the
MgCO3 will not dissolve to any appreciable extent.
Method B: You could attempt a flame test to determine which salt is which. Na+ ions give
an orange flame while Mg2+ ions do not give a positive flame test. This method may not give
a clear answer, though, if the flame test loop is old/cheap as it is common for loops to
contain some sodium. An equivalent approach which might give better results would be to
put each salt in a petri dish, pour a little alcohol over each then burn the alcohol and see
which flame turned orange (like the demo in class).
(b)
You’re given two vials, each containing a solid sample of metal. You’re told that one vial
contains aluminum and the other contains potassium. How do you determine which metal is
which? Briefly, explain how your method will tell you which is which.
Method A: Potassium is a lot softer than aluminum. It should be possible to cut a small
sample of potassium into pieces using a spatula. This should not be possible for aluminum.
Method B: Potassium reacts violently with water; aluminum does not react at all with
water. Set up a beaker of water behind a blast shield. Drop a small piece of one metal into
the water. If there is no reaction, it was aluminum. If there is a violent reaction, it was
potassium. Repeat the procedure with the other metal to confirm that only one reacts.
Method C: Weigh a sample of each metal then determine its volume by displacement of an
inert liquid such as oil. Use the mass and volume of each piece of metal to determine its
density. As an alkali metal, potassium will be less dense than aluminum. Method C is less
practical than methods A and B.
4.
(a)
[4 marks]
Carbonate salts of the alkaline earth metals are insoluble in water but react readily with acid.
Draw a balanced chemical reaction between calcium carbonate (CaCO3) and hydrochloric
acid (HCl). Include all states of matter.
CaCO3(s) + HCl(aq)
CaCl2(aq) + CO2 (g) + H2O(l)
NAME:_________________________
(b)
Section:_____
Student Number:________________
We learnt in class that calcium and magnesium cations were responsible for hard water. If
these calcium and magnesium salts are insoluble in neutral water, briefly explain how these
ions come to be dissolved in water. Include balanced chemical equations for any relevant
reactions
Tap water is not neutral but slightly acidic. CO2 from the air dissolves in water to
form carbonic acid.
H2O(l) + CO2(g)
H2CO3(aq)
H2CO3(aq) + H2O(l)
H3O+(aq) + HCO3-(aq)
Both CaCO3 and MgCO3 are soluble in acidic solutions.
CaCO3(s) + H3O+(aq)
Ca2+(aq) + HCO3-(aq) + H2O(l)
5.
For each of the molecules/ions listed below:
[8 marks]
(a) Draw its best Lewis structure (include any non-zero formal charges on the appropriate
atoms).
(b) Indicate the molecular geometry around the central atom.
(c) Give the approximate bonds angles.
(a)
CO32-
O
Trigonal Planar, 120°
C
O
(b)
O
ClF3(Cl is central)
F
T-Shaped, 90 & 180°
F
Cl
F
(c)
XeF4
F
F
Xe
F
F
Square Planar, 90°
NAME:_________________________
Section:_____
Student Number:________________
6.
Sodium metal is produced industrially by the electrolysis of molten sodium chloride.
[8 marks]
(a)
Why is molten sodium chloride required for this procedure to work?
Ionic solids cannot conduct electric currents and an electric current is necessary for
electrolysis.
(b)
Why isn’t an aqueous solution of sodium chloride used instead of molten sodium chloride?
Because H+ is easier to reduce than Na+ and you will form H2 gas instead of Na metal.
(c)
Give the two half-reactions for the production of sodium metal (include all states of matter).
2 Na+(l) + 2 e- → Na (l)
2 Cl-(l) → Cl2(g) + 2e-
(d)
What by-product is formed during the electrolysis of sodium chloride?
Chlorine gas
(e)
During the electrolysis of sodium chloride, the newly formed sodium metal and the byproduct are kept separate. Why?
They must be kept separate because they will react to form NaCl.
(f)
What method is used for the industrial production of potassium metal?
Chemical reduction:
(g)
KCl + Na → NaCl + K
Briefly explain why potassium metal is not produced by electrolysis.
Because molten potassium metal is soluble in molten potassium chloride.
NAME:_________________________
Section:_____
Student Number:________________
7.
There are two valid resonance structures for dinitrogen oxide (N2O, nitrogen is central).
[6 marks]
(a)
Draw each of the two valid resonance structures (Include any non-zero formal charges on
the appropriate atoms).
N
N
O
N
N
O
(b)
Circle the better resonance structure (the resonance structure which more closely resembles
the true/averaged structure of this anion. You will only obtain credit for part (b) if your
answers to part (a) are correct.
8.
Write a balanced chemical equation for each of the following reactions. Include states of
matter. If no reaction occurs, write “NO REACTION” instead.
[6 marks]
(a)
Calcium is added to liquid bromine.
Ca(s) + Br2(l) → CaBr2(s)
(b)
Magnesium is added to aqueous HCl
Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
(c)
Beryllium is added to water.
no reaction
(d)
Lithium is reacted with excess oxygen.
4 Li(s) + O2(g)
(e)
→
2 Li2O(s)
Aluminium is added to concentrated aqueous NaOH.
2Al(s) + 6H2O(l) + 2OH-(aq)
or
→
2Al(s) + 6H2O(l) + 2NaOH(aq)
2[Al(OH)4]-(aq) + 3H2(g)
→
2Na[Al(OH)4](aq) +
3H2(g)
NAME:_________________________
Section:_____
Student Number:________________
An element has a density of 10.50 g/cm3 and a metallic radius of 144.5 pm. The metal
crystallizes in a lattice as shown below:
[10 marks]
9.
x
4r
x
(a)
What type of lattice is this?
Face Centered Cubic
(b)
Calculate the volume of one unit cell of this lattice.
1m
144.5pm
1.445
1 10 pm
10
m
4
2
16
8
√8
1.445
10
4.0870772
V
√8
10
4.0870772
m
10
V 6.82713551 10
m
(c)
Identify the element by calculating its atomic mass (in u).
10.50
1
1000
10500
6.82713551
107.9
1000000
1
10
10500
1
4
1
1.6605
10
107.9266815
NAME:_________________________
10.
(a)
Section:_____
Student Number:________________
[6 marks]
Sketch a Born-Haber cycle diagram for PbO. Clearly label the enthalpy change involved
with each step. (i.e. give the name or symbol for each enthalpy change).
Pb2+(g)
+
O2-(g)
EAH2(O-)
I2(Pb)
Pb+(g)
O-(g)
LFH (PbO)
EAH1(O)
I1(Pb)
Pb(g)
+
sublH(Pb)
Pb(s)
(b)
+
O(g)
xBD(O2)
1/2 O2(g)
fH (PbO)
PbO(s)
Use your Born-Haber cycle and the information from the data sheet to calculate ΔLFH for
PbO.
ΔfH = ΔsublH + I1 + I2 +1/2 ΔBDH + ΔEAH1 + ΔEAH2 +ΔLFH
ΔLFH = ΔfH – (ΔsublH + I1 + I2 +1/2 ΔBDH + ΔEAH1 + ΔEAH2)
ΔLFH = -3567 kJ/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
9
2 -2
Coulomb constant (1/(4)) 8.988 × 10 N·m ·C
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
Planck's constant
Proton mass
Neutron mass
Rydberg Constant (RH)
Speed of light in vacuum
Standard atmospheric pressure
6.626  10-34 J·Hz-1
1.0072765 u
1.0086649 u
2.179  10-18 J
2.9979  108 m·s-1
1 bar = 100 kPa
Formulae
E  h
c  
rn  a0
n2
Z
En  RH
 
p  mv
Z2
n2
Ek 
1 (z  e)(z e)
F 
4
d2
1
mv 2
2
h
p
x  p 
PV  nRT
1 (z  e)(z e)
E 
4
d
Radius Ratio Data
minimum
ZnS
NaCl
CsCl
r
r
0.225
0.414
0.732
Some Thermodynamic Data (all values in kJ/mol)_
+195.20
+498
ΔsublH(Pb)
ΔBDH(O=O)
I1(Pb)
I2(Pb)
ΔEAH(Pb)
+715.6
+1450.5
-35.1
I1(O)
I2(O)
ΔEA1H(O)
ΔEA2H(O)
+1314
+3388
-141.0
+881
ΔfH°(PbO)
-217.3
h
4
NAME:_________________________
1
Section:_____
Student Number:________________
CHEM 1000 Standard Periodic Table
18
1.0079
4.0026
H
He
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
1
2
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
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)
107
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