Chemistry 12
January 2004 Provincial Examination
ANSWER KEY / SCORING GUIDE
CURRICULUM:
Organizers
1.
2.
3.
4.
5.
Sub-Organizers
Reaction Kinetics
Dynamic Equilibrium
Solubility Equilibria
Acids, Bases, and Salts
Oxidation – Reduction
A, B, C
D, E, F
G, H, I
J, K, L, M, N, O, P, Q, R
S, T, U, V, W
Part A: Multiple Choice
Q
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
K
D
B
D
B
D
D
D
C
C
B
A
B
B
A
C
B
D
D
B
A
D
B
A
D
B
A
D
A
A
A
C
K
U
U
U
U
U
U
H
U
K
U
U
U
U
U
U
U
U
U
U
U
U
U
E
L
U
U
U
K
U
H
S
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
E
1
1
1
1
1
1
CO PLO
1
A6
1
A4
1
B3
1
B6, C4
1
C2
1
C5, B2
2
D2
2
D4
2
D7
2
D9
2
E4
2
E3
2
F2
2
F3
2
F5
2
F7
2
F8
3
G1
3
G4
3
H1
3
H2
3
H6
3
I2
T E D
3
I5
3
I6
4
J2
4
J6
4
J8
4
K1, 3, 4
Q
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
K
D
A
C
A
D
B
D
A
C
C
D
B
B
A
C
D
C
A
C
C
B
C
C
C
D
B
B
C
A
A
C
U
U
U
U
E
L
U
U
U
K
U
K
U
H
H
K
K
U
U
U
U
U
U
U
H
U
K
U
U
K
U
S
1
1
1
1
E
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
CO PLO
4
K6
4
K6, M2
4
L10
4
L12
T E D
4
M4
4
N1
4
N3
4
O1
4
O4
4
P5
4
P3
4
Q1
4
Q4
4
R1
4
R4
5
S1, 2
5
S1
5
S2
5
S2
5
S4
5
S6
5
T3
5
U2
5
U2, L11
5
U6
5
U3, 5
5
V3
5
W1
5
W4
Multiple Choice = 60 marks
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February 27, 2004
Part B: Written Response
Q
B
C
S
CO
PLO
1.
2.
3.
4.
5.
6.
7.
8.
1
2
3
4
5
6
7
8
U
U
U
U
U
U
U
U/H
5
3
3
4
5
3
4
3
1
2
3
4
4
4
5
5
A3, 5
E2
H2, 3, I6
J7, K6, 8
M3, N2
P1
T2
W6
Written Response = 30 marks
Multiple Choice = 60 (60 questions)
Written Response = 30 (8 questions)
EXAMINATION TOTAL = 90 marks
LEGEND:
Q = Question Number
K = Keyed Response
B = Score Box Number
S = Score
PLO = Prescribed Learning Outcome
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C = Cognitive Level
CO = Curriculum Organizer
February 27, 2004
PART B: WRITTEN RESPONSE
Value: 30 marks
Suggested Time: 40 minutes
INSTRUCTIONS: You are expected to communicate your knowledge and understanding of chemical
principles in a clear and logical manner. Your steps and assumptions leading to a
solution must be written in the spaces below the questions. Answers must include
units where appropriate and be given to the correct number of significant figures.
For questions involving calculations, full marks will NOT be given for
providing only an answer.
1. The release of O2( g ) resulting from the decomposition of bleach was measured in
two different experiments. Data was collected and the following graph was drawn:
70
Experiment 1
60
Volume
O2
(mL)
Experiment 2
50
40
30
20
10
1.0
2.0
3.0
4.0
5.0
Time (min)
a) Calculate the average rate of reaction for each experiment.
(2 marks)
Solution:
For Example:
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Experiment 1:
60 mL
= 24 mL min
2.5 min
¨ 1 mark
Experiment 2:
50 mL
= 11 mL min
4.5 min
¨ 1 mark
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February 27, 2004
b) Identify a variable from Experiment 1 and how it was changed to produce the
different reaction rate for Experiment 2. Explain using collision theory.
(3 marks)
Solution:
For Example:
Variable/Change
Explanation
Temperature is decreased.
Lower fraction of effective
collisions.
OR
Concentration of reactants was
decreased.
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Fewer collisions.
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˝ ¨ 3 marks
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February 27, 2004
2. Consider the following equilibrium system:
C( s ) + 2 H 2 ( g ) Æ
¨ CH 4( g )
DH = -75 kJ
State three different ways to make more C( s ) react.
(3 marks)
Solution:
For Example:
Any three of the following:
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•
add H 2
•
remove CH 4
•
decrease temperature
•
increase pressure/decrease volume
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˝ ¨ 3 marks
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February 27, 2004
3. Sufficient Na 2SO 4( s ) is added to 0.10 M Ba (NO 3 )2 to cause a precipitate to form.
a) Write the net ionic equation for the precipitate formation.
(1 mark)
Solution:
For Example:
¨ 1 mark
2-
Ba 2(+aq ) + SO 4 ( aq ) Æ BaSO 4( s )
[
]
b) Calculate the SO 42- at the moment the precipitate starts to form.
(2 marks)
Solution:
For Example:
[
2SO 4
¸
Ô
Ô
˝ ¨ 1 mark
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˛
K sp
] = [Ba ]
2+
=
1.1 ¥ 10 -10
0.10
= 1.1 ¥ 10 -9 M
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¨ 1 mark
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February 27, 2004
4. a) Write the equation to represent the reaction that results when NH 4+ ions are
mixed with HCO3 - ions.
(2 marks)
Solution:
For Example:
NH 4+( aq ) + HCO3 -( aq ) Æ
¨ NH 3( aq ) + H 2 CO3( aq )
¸Ô
˝ ¨ 2 marks
Ô˛
b) Identify the two bases in the reaction in part a).
(1 mark)
Solution:
For Example:
¸
˝ ¨ 1 mark
˛
HCO3 - and NH 3
c) Predict whether the reaction will favour the reactants or products.
Justify your answer.
(1 mark)
Solution:
For Example:
Prediction: Reactants
Justification: K a H2 CO3 > K a
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NH4+
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¨
1
2
mark
¨
1
2
mark
February 27, 2004
5. Calculate the pH of 0.60 M NH 4 I . Start by writing the equation for the
predominant equilibrium reaction.
(5 marks)
Solution:
For Example:
+
+ H 2 O( l ) Æ
¨ H 3O ( aq )
NH 4+( aq )
[I]
0.60
[C ]
-x
[E] 0.60 - x
+ NH 3( aq )
0
0
+x
+x
x
x
¨ 1 mark
¸
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˝ ¨ 1 mark
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(assume x is negligible)
[H O ][NH ]
=
[NH ]
+
Ka
3
3
+
4
5.6 ¥ 10 -10 =
( x )( x )
(0.60)
[
¨ 1 mark
]
x = H 3O + = 1.83 ¥ 10 -5 M
¨ 1 mark
pH = 4.74
¨ 1 mark
( Deduct 12 mark for incorrect significant figures.)
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February 27, 2004
(
6. A solution of NaOH( aq ) was standardized by titration using oxalic acid H 2 C 2 O 4( s )
as the primary standard. The following data was collected:
)
Mass of H2C 2O 4( s ) used = 1.02 g
Volume of NaOH( aq ) used = 40.6 mL
Calculate the concentration of the NaOH( aq ) .
(3 marks)
Solution:
For Example:
H2C 2O 4( s ) + 2NaOH( aq ) Æ Na 2C 2O 4( aq ) + 2H2O( l)
Moles of H2C 2O 4( s ) = 1.02 g ¥
mol
= 1.133 ¥ 10 -2 mol
90.0 g
(
)
Moles of NaOH = 2 1.13 ¥ 10 -2 mol = 2.267 ¥ 10 -2 mol
2.26 ¥ 10 -2 mol
[NaOH] = 0.0406 L = 0.558 M
¨ 1 mark
¨ 1 mark
¨ 1 mark
( Deduct 12 mark for incorrect significant figures.)
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February 27, 2004
7. Balance the following skeletal redox equation in acidic solution:
MnO 4- + As2 O3 Æ Mn 2 + + AsO 43-
(4 marks)
(acidic)
Solution:
For Example:
(5e - + 8H + + MnO4- Æ Mn2 + + 4H2O) ¥ 4
(5H2O + As2O3 Æ 2AsO43- + 10 H + + 4e - ) ¥ 5
20 e - + 32 H + + 4 MnO 4- + 25H 2 O + 5As2 O3 Æ 4 Mn 2 + + 16H 2 O + 10 AsO 43- + 50 H + + 20 e 4 MnO 4- + 9H 2 O + 5As2 O3 Æ 4 Mn 2 + + 10 AsO 43- + 18H +
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˝ ¨ 4 marks
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February 27, 2004
8. Draw an electrolytic cell that could be used to plate an iron ring with gold.
Be sure to include all of the necessary parts. In addition, label the anode, solution
used and composition of the electrodes.
(3 marks)
Solution:
For Example:
+
DC
Power
Source
¸
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Ô
˝ ¨ 3 marks
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–
Au
(Anode)
Iron Ring
(Cathode)
Au(NO 3 ) 3(aq )
END OF KEY
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February 27, 2004