June 2011
Chemistry Examination Answers
551-504
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 1
4.4
Appropriate responses and marking scale
Part A: Chemistry of Aquarium Gases
Question 1
Example of appropriate responses
-
The oxygen and ammonia gas molecules travel in a straight-line motion.
-
The gas volumes of oxygen and ammonia are negligible.
-
Collisions between oxygen and ammonia gas molecules are perfectly elastic (that is, no
energy is gained or lost during the collision), and there are no attractive or repulsive forces
between the oxygen and ammonia gas molecules.
-
The average kinetic energy of the oxygen and ammonia gas particles depends only on the
temperature of the system.
Note: Accept any other appropriate answer.
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
All four points are stated and are correct.
Only three points are stated and are correct.
Only two points are stated and are correct.
Only one point is stated and is correct.
No correct points or no answer given.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 2
Question 2
Example of appropriate responses
a)
Partial pressure of ammonia
Pt  PO2  PH2O  PN2  PNH3
101 .3 kPa  36.1 kPa  0.600 kPa  63.3 kPa  x kPa
PNH3  1.3 kPa
Marking Scale
2 marks
1 mark
0 marks
b)
Appropriate procedure and correct answer.
Appropriate procedure, but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Inappropriate procedure or did not show the procedure, regardless of the answer.
Moles of dissolved gases
Step 1: Moles of dissolved oxygen
PV  nRT
36.1 kPa 0.303 L   n 8.31 kPa L/mol K  298 K 
n  4.42  10 3 mol
Step 2: Moles of dissolved NH3
PV  nRT
1.3 kPa 0.303 L   n 8.31 kPa L/mol K  298 K 
n  1.6  10  4 mol
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
Appropriate procedure and correct answer.
Appropriate procedure, but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Appropriate procedure but incorrect answer because of major mistakes.
Partially appropriate procedure, regardless of the answer.
Inappropriate procedure or did not show the procedure, regardless of the answer.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 3
Question 3
Example of an appropriate response
molar mass oxygen  32.0 g/mol
molar mass water vapour  18.0 g/mol
molar mass nitrogen  28.0 g/mol
molar mass ammonia  17.0 g/mol
The lower the molar mass, the higher the rate of diffusion
O2, N2, H2O, NH3
Marking Scale
3 marks
2 marks
1 mark
0 marks
Justification and order is correct.
Justification is correct but minor error in calculation of a molar mass.
Correct order and no justification.
Incorrect justification or no answer given.
Question 4
Example of an appropriate procedure
Step 1: Moles of NH3
n  c V
 5.88  10 5 mol/L  40.0 L
 2.35  10 3 mol NH3
Step 2: Moles of O2
7 mols O2
 2.35  10 3 mol NH3
4 mols NH3
 4.11  10 3 mol O2
Step 3: Volume of O2 (May also be solved using PV=nRT.)
1 mol SATP  24.5 L
24.5 L
at SATP  4.11  10 3 mol O 2
mol
 1.01 10 1 L O 2
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
Appropriate procedure and correct answer.
Appropriate procedure, but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Appropriate procedure but incorrect answer because of major mistakes.
Partially appropriate procedure, regardless of the answer.
Inappropriate procedure or did not show the procedure, regardless of the answer.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 4
Part B: Natural Gas and Energy
Question 5
Example of an appropriate procedure
Step 1: Find n of butane
n  mass / molar mass
n  5.8 g / 58 g/mol
n  0.10 moles of butane
Step 2: Set up ratio between energy and n of butane
1 mol butane 0.10 mol of butane

 2657 .4 kJ
x kJ
x   265 .74 kJ of energy released for 0.10 moles of butane
Step 3
Qwater   Qbutane
Qw   265 .74 kJ  265 740 J
Qw  m  c  T
T  Qw / m  c 
T  265 740 J / 1000 g  4.19 J/gC
T  63.4C
Tf  T  Ti
Tf  63.4  20.0 C
Tf  83C
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
Appropriate procedure and correct answer.
Appropriate procedure, but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Appropriate procedure but incorrect answer because of major mistakes (ex. Student
solved for ∆T and did not solve for Tf or students did not convert L to g and kJ to J)
Partially appropriate procedure, regardless of the answer.
Inappropriate procedure or did not show the procedure, regardless of the answer.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 5
Question 6
Example of an appropriate response
Reverse Eq. #1:
Use Eq. #2:
Double Eq. # 3:
From the diagram
CH4 (g)
C (s) + O2 (g)
2H2 (g) + O2(g)
CH4 (g) + 2 O2 (g)




C (s) + 2H2 (g)
CO2 (g)
2H2O (g)
CO2(g) + 2H2O (g)
∆H = +74.6 kJ
∆H = 393.5 kJ
∆H = 484 kJ
∆H = 803 kJ
The heat of combustion for methane is −803 kJ/mol.
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
Appropriate procedure and correct answer.
Appropriate procedure, but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Appropriate procedure but incorrect answer because of major mistakes (ex. incorrect
sign on the ∆H value(s).
Partially appropriate procedure regardless of the answer.
Inappropriate procedure or did not show the procedure, regardless of the answer.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 6
Question 7
Example of appropriate responses
a)
Enthalpy (kJ)
Enthalpy vs. Progress of Reaction
C2H6 (g) + 7 O2(g)
2
EA = 102 kJ
H = -1560 kJ
2CO2(g) + 3 H2O(g)
Progress of Reaction
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
b)
Appropriate and correct diagram, includes title, correctly labelled plateaus, axes and
Ea, ∆H values.
Partially appropriate diagram, omitted one out of the five components of the diagram.
Partially appropriate diagram, but made major omissions such as forgetting two of
the five components of the diagram.
Partially appropriate diagram, provided only one or two components.
Inappropriate diagram or did not draw a diagram.
∆H = +1560 kJ
Ea = +1662 kJ
Marking Scale
2 marks
1 mark
0 marks
Two correct answers.
One correct answer.
No correct answers or no answer given.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 7
Part C: Reaction Rates and the Human Body
Question 8
Example of appropriate responses
a)
75 kg man:
mass O 2
moles O 2 
molar mass O 2
moles O 2 
100 kg man:
3.5 g
32 g/mol
moles O 2  0.0109 moles
moles of glucose :
mass O 2
molar mass O 2
moles O 2 
4.2 g
32 g/mol
moles O 2  0.0131 moles
moles of glucose :
glucose : O 2  1 : 6
moles O 2
moles glucose 
6
0.0109 moles

6
 0.018 moles
Answer:
moles O 2 
glucose : O 2  1 : 6
moles O 2
moles glucose 
6
0.0131 moles

6
 0.022 moles
The 75 kg man uses 0.018 moles of glucose in 10 minutes.
The 100 kg man uses 0.022 moles of glucose in 10 minutes.
Note: There are two different thoughts on the ambiguous zero (significant figures). Please
correct your students work based on your teachings.
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
b)
Appropriate procedure and correct answer.
Appropriate procedure but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Appropriate procedure but incorrect answer because of major mistakes.
Partially appropriate procedure and incorrect answer.
Inappropriate procedure and incorrect answer.
Rate law expression is Rate = k[C6H12O6] [O2]6.
Marking Scale
2 marks
1 mark
0 marks
c)
Correctly states the rate law expression.
Does not apply.
Incorrectly states rate law expression.
There are no differences in the rate law expression because both are derived from
the cellular respiration equation.
Marking Scale
2 marks
1 mark
0 marks
Correct answer and justification.
Correct answer without any justification.
Incorrectly compares rate law expressions.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 8
Question 9
Example of an appropriate response
-
Use powdered marble chips (calcium carbonate).
Increasing the surface area increases the probability of effective collisions.
-
Increase the concentration of HCl.
Increasing the concentration of HCl increases the probability of effective collisions.
-
Heat HCl solution.
Increasing the temperature of the reactants increases the kinetic energy of the reactants
and therefore increases the probability of effective collisions and the probability that the
collisions will have sufficient energy for a transformation to take place.
-
Add a catalyst.
The catalyst reduces the activation energy barrier for the reaction and therefore increases
the probability of effective collisions.
Marking Scale
3 marks
2 marks
1 mark
0 marks
Three correct methods with appropriate use of collision theory are provided.
Two correct methods with appropriate use of collision theory are provided.
One correct method with appropriate use of collision theory is provided OR three
correct methods, but did not use collision theory.
Answers are incorrect.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 9
Part D: Chemistry and the Human Body (Equilibrium)
Question 10
Example of appropriate responses
a)
At high altitudes, there is less oxygen in the air. The stress of a reduced oxygen
concentration results in a shift in equilibrium to the reactant side, which lowers the
concentration of oxyhemoglobin, HbO2.
Marking Scale
1 mark
0 marks
b)
Correct answer.
Incorrect answer or no answer given.
Increase the concentration of oxygen, which will alleviate the stress, and re-establish a
new equilibrium.
Marking Scale
1 mark
0 marks
Correct answer.
Incorrect answer or no answer given.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 10
Question 11
a)
Decrease the bicarbonate ion ( HCO 3 ) concentration in the blood. Decreasing the blood's
concentration of HCO 3 shifts the equilibrium reaction toward the right to compensate for
the loss in HCO 3 . When the equilibrium shifts to the right, more H+ ions are generated
together with HCO 3 ions. As a result, the pH decreases.
Marking Scale
2 marks
1 mark
Correct answer.
Partially correct answer (ex. does not explain how removal of bicarbonate ion affects
blood).
Incorrect answer or no answer given.
0 marks
b)
Example of an appropriate response
H+(aq) + HCO3 aq 
H2CO3(aq)
Ka 
7.94  10 7 
H HCO 


3
H2 CO3
H  2.77  10 

2
1.10  10 3
H   3.15  10

8
mol/L
pH  7.50
Answer:
The athlete is suffering from alkalosis, but the pH is not lethal.
Note: An equation describing the condition would be acceptable.
Note: As this is the second part of a two part equilibrium reaction, the bicarbonate ion
concentration at equilibirum is not equal to the hydrogen ion concentration at equilibrium.
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
Appropriate procedure and correct answer.
Appropriate procedure but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Appropriate procedure but incorrect answer because of major mistakes.
Partially appropriate procedure and incorrect answer.
Inappropriate procedure and incorrect answer.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 11
Question 12
Example of an appropriate procedure
Calculation of fluoride ion concentration in the water

 
K sp  Ca2 F 
2
3.9  10 11  x  2 x 
2
x
3
3.9  10 
11
4
x  2.1  10  4 mol/L Ca2

F   2  2.1 10 mol/L
F   4.2  10 mol/L


4

4
The fluoride ion concentration is 4.2  10-4 mol/L.
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
Appropriate procedure with correct answer.
Appropriate procedure but incorrect answer because of minor mistakes such as a
calculation or transcription error, or an incorrect or missing unit of measure.
Appropriate procedure and incorrect answer because of major mistakes.
Partially appropriate procedure but incorrect answer.
Inappropriate procedure and incorrect answer.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 12
Question 13
Example of appropriate responses
The volume and uncertainty of measurement of gas in the syringe A is 15 mL ± 5 mL.
The volume and uncertainty of measurement of gas in the syringe B is 15.0 mL ± 0.5 mL.
Marking Scale
4 marks
3 marks
2 marks
1 mark
0 marks
Volume of both gases correct with correct significant figures and correct uncertainty.
One error involving significant figures or uncertainty.
Two errors involving significant figures or uncertainty.
Three errors involving significant figures or uncertainty.
Incorrect answer or no answer given.
Marking Guide for Significant Figures (for consistent use during the entire exam)
Use this marking scale to assess the use of significant figures throughout the first 12 questions
of the examination. Do not take into account work from question 13 for this mark.
Marking Scale
2 marks
1 mark
0 marks
Appropriate and consistent use of significant figures.
Partially appropriate use of significant figures and/or inconsistent use of significant
figures.
Inappropriate use of significant figures or does not take into account significant
figures.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 13
Feedback Questionnaire
Chemistry Examination – Secondary Cycle 2 Year 3
Theory Examination – June 2011
Please comment on the following:
1.
Time allotted for theory examination:
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
2.
Students’ level of interest:
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
3.
Level of difficulty:
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
4.
Administration and Marking Guide (quality and clarity):
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
5.
Other comments:
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
6.
Please list any errors or omissions:
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Please return questionnaire to your school board Science and Technology consultant.
Thank You.
Chemistry Examination – 551-504
Secondary Cycle Two Year Three
Theory Examination
Administration and Marking Guide
Page 14