Chemistry 12
[Pages:14]Chemistry 12
April 2003 Provincial Examination
ANSWER KEY / SCORING GUIDE
CURRICULUM:
Organizers 1. Reaction Kinetics 2. Dynamic Equilibrium 3. Solubility Equilibria 4. Acids, Bases, and Salts 5. Oxidation ? Reduction
Sub-Organizers 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 K C S CO PLO
QKC S
1. D U 1 1 A4
25. C U 2
2. C K 1 1 A6
26. C K 1
3. C U 1 1 B5
27. D K 1
4. A K 1 1 B9
28. C U 1
5. A U 2 1 C4
29. A U 1
6. C U 1 1 C6
30. D U 1
7. C K 1 2 D4
31. C U 2
8. B K 2 2 D8
32. B K 1
9. D H 2 2 E2
33. A U 2
10. C K 1 2 E4
34. D U 2
11. B U 1 2 F2
35. A U 1
12. A U 1
2 D4, F3
36. C K
1
13. D U 1 2 F3
37. D K 1
14. D U 1 2 F4
38. A H 1
15. C K 1 3 G4
39. C U 1
16. D H 1 3 G6
40. C U 1
17. D U 1 3 G8
41. A U 1
18. C U 1 3 H2
42. B U 1
19. B U 2 3 H5
43. B U 2
20. B U 1 3 I2
44. A H 2
21. D U 2 3 I3
45. C U 1
22. A U 1 3 I6
46. A U 1
23. B U 1 4 J7
47. D U 2
24. C K 1 4 J11
48. B H 1
Multiple Choice = 60 marks (48 questions)
CO PLO
4 K1, 2, 3, 4 4 K7 4 L8 4 L11 4 M4 4 N2 4 N4 4 O2 4 O4 4 P2 4 P4 4 P6 4 Q3 5 S1 5 S1 5 S2 5 S5, 6 5 S2, 3 5 U2 5 U3, 5 5 U9 5 U7 5 W4 5 W4, 7
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Part B: Written Response
Q
B
C
1.
1
U
2.
2
U
3.
3
H
4.
4
U
5.
5
U
6.
6
U
7.
7
U
8.
8
U
9.
9
U
10.
10
U
11.
11
H
S
CO
PLO
5
1
A3
2
1
B1
2
2
E5
3
2
F6
6
3
H3
4
4
J3, 12, K8
4
4
L6, 10
4
4
M3
3
5
S4
3
5
T2
4
5
W2, 4, 7
Written Response = 40 marks
Multiple Choice = 60 (48 questions) Written Response = 40 (11 questions) EXAMINATION TOTAL = 100 marks
LEGEND: Q = Question Number K = Keyed Response B = Score Box Number S = Score PLO = Prescribed Learning Outcome
C = Cognitive Level CO = Curriculum Organizer
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PART B: WRITTEN RESPONSE
Value: 40 marks
Suggested Time: 50 minutes
INSTRUCTIONS: You will be 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. Consider the following reaction:
( ) 3Cu(s) + 8HNO3(aq) ? 3Cu NO3 2(aq) + 2NO(g) + 4H2O(l)
A piece of copper is added to a nitric acid solution in an open beaker, allowing the NO(g) to escape. The following data was obtained:
TIME (min)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
MASS OF BEAKER AND CONTENTS (g)
200.00 197.50 195.45 193.55 191.70 189.90 188.15 186.45 184.80
Copper
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a) Calculate the reaction rate for the time period 2.0 to 6.0 min . Solution: For Example:
rate
=
mass time
change change
=
195.45 g - 188.15 g
(6.0 - 2.0) min
=
7.30 g 4.0 min
= 1.8 g min NO produced
( ) Deduct
1 2
mark
for
incorrect
significant
figures.
(2 marks)
?
?
?
?
?
2
marks
?
?
?
b) Calculate the mass of copper consumed in the first 5 minutes. Solution: For Example:
(3 marks)
moles
NO
produced
=
200.00 g - 189.90 g 30.0 g mol
=
0.3367 mol
NO
? ? 1 mark
moles
Cu
consumed
=
0.3367 mol
NO
?
3 mol Cu 2 mol NO
=
0.5050 mol
Cu
? ? 1 mark
mass Cu consumed = 0.5050 mol Cu ? 63.5 g Cu = 32.1 g Cu 1 mol Cu
? ? 1 mark
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2. Using collision theory, explain why reactions between two solutions occur more rapidly than reactions between two solids.
(2 marks)
Solution:
For Example:
? Particles must be able to collide to react.
? Only the particles on the surface of a solid are available for reaction. In a solution, all particles are available.
? ? ? 2 marks ?
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3. Consider the following reaction for the Haber Process for ammonia production:
N2(g) + 3H2(g) ? 2NH3(g)
DH = -92 kJ
The system is normally maintained at a temperature of approximately 500C.
a) Explain why 1000C is not used. Solution: For Example:
Equilibrium will be shifted to the left, reducing the yield of NH3 . ? 1 mark
(1 mark)
b) Explain why 100C is not used. Solution: For Example:
The rate of the reaction would be too low.
(1 mark) ? 1 mark
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4. Consider the following equilibrium: SO3(g) + NO(g) ? NO2(g) + SO2(g)
In an experiment, 0.100 moles of SO3 and 0.100 moles of NO are placed
in a 1.00 L container. When equilibrium is achieved, [NO2 ] = 0.0414 mol L.
Calculate the Keq value.
Solution:
For Example:
(3 marks)
SO3 + NO ? NO2 + SO2
[I] 0.100
0.100
0
0
[C] -0.0414 -0.0414
+0.0414 +0.0414
[E] 0.059
0.059
0.0414
0.0414
?
?
?
?
?
1
1 2
marks
?
?
?
Keq
=
[NO2 ][SO2 ] [SO3][NO]
=
(0.0414) (0.0414) (0.059) (0.059)
= 0.50
??
?
?
1 2
mark
? 1 mark
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5. a) Write the net ionic equation for the reaction between Pb(NO3)2(aq) and NaCl(aq) .
(2 marks)
Solution:
For Example:
Pb2(+aq)
+
2Cl
-
(aq
)
?
PbCl2(s)
? 2 marks
b) Determine, with calculations, whether a precipitate will form when
15.0 mL of 0.050 M Pb(NO3)2 is added to 35.0 mL of 0.085 M NaCl.
Solution:
For Example:
(4 marks)
[ ] Pb2+ = 0.050 M ? 15.0 mL = 0.015 M 50.0 mL [ ] Cl- = 0.085 M ? 35.0 mL = 0.0595 M 50.0 mL
[ ][ ] Trial Ksp = Pb2+ Cl- 2 = (0.015) (0.0595)2 = 5.3 ? 10-5
Ksp for PbCl2 = 1.2 ? 10-5 Since Trial Ksp > Ksp , a precipitate does form.
? ? 1 mark ? ? 1 mark
? 1 mark
? 1 mark
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