2012 Senior External Examination
Chemistry
Paper Two — Question book
Monday 5 November 2012
1 pm to 3:10 pm
Time allowed
• Perusal time: 10 minutes
• Working time: 2 hours
Examination materials provided
• Paper Two — Question book
• Paper Two — Resource book
• Paper Two — Response book
Equipment allowed
• QSA-approved equipment
• non-programmable calculator
Paper Two is an open book examination. You may refer to any paper-based material that you have brought into
the examination room.
Directions
You may write in this book during perusal time.
Paper Two has five questions of equal value.
Attempt four questions only.
Assessment
Assessment standards are at the end of this book.
After the examination session
Take this book when you leave.
Planning space
Complex reasoning processes
Paper Two has five questions of equal value. Attempt four questions only.
In each response, give full reasoning in terms of your knowledge and application of Chemistry
and use the range of scientific processes and complex reasoning objectives learned during your
study of the subject.
Write your responses in the response book.
Grade descriptions for each question are provided below.
A grade:
• Has arrived at a valid response.
• Has successfully demonstrated logical reasoning and critical thinking.
• Has made few, if any, (minor) errors.
B grade:
• Has made substantial progress towards an appropriate response.
• Has applied logical reasoning and critical thinking.
C grade:
• Has made some progress towards an appropriate response.
• Has demonstrated some logical reasoning and critical thinking.
D grade:
• Response is unintelligible or does not satisfy the requirements for any other grade.
2012 Chemistry — Paper Two — Question book
1
Question 1
Nitrogen gas can be prepared by passing gaseous ammonia over solid copper (II) oxide at high
temperatures. The other products are solid copper and water vapour.
181 g of NH3 ( g) is placed in a container with 190.4 g of copper (II) oxide at high temperature. What
mass of nitrogen gas will actually be formed if the process is 65% efficient?
Question 2
The following fictional half-cells were constructed.
•
•
•
•
A strip of metal X in a beaker containing a 1.0 M X nitrate solution
A strip of metal Y in a beaker containing a 1.0 M Y nitrate solution
A strip of metal Z in a beaker containing a 1.0 M Z nitrate solution
A strip of metal A in a beaker containing a 1.0 M A nitrate solution
The results of coupling half-cells using appropriate wires, voltmeters and salt bridges to form
electrochemical cells are as follows.
X2 + /X with Y3 + /Y gave a potential difference of 0.44 volts and the mass of the Y electrode
was found to increase.
ii. Z2 + /Z and A2 + /A gave a potential difference of 0.78 volts and the colour of the Z nitrate
solution was noted to get more intense (deeper colour).
iii. X2 + /X and Z2 + /Z gave a potential difference of 0.74 volts and the centre reading voltmeter
deflected in the same direction as in i above.
iv. X2 + /X and A2 + /A gave a potential difference of 1.52 volts.
v. Only one of the half-cells was reduced when they were connected to the standard H+ /H2
half-cell; the potential difference was 0.34 volts.
i.
Use the information above to construct a table of standard reduction potentials. Your table must show
the relevant half-reactions and standard electrode potentials in correct order. Show all working.
Question 3
Calculate the H for the reaction
N 2 H 4  l  + O 2  g   N 2  g  + 2H 2 O  1 
given the following data.
2
2NH 3  g  + 3N 2 O  g   4N 2  g  + 3H 2 O  l 
H = – 1010 kJ
N 2 O  g  + 3H 2  g   N 2 H 4  l  + H 2 O  l 
H = – 317 kJ
1
2NH 3  g  + --- O 2  g   N 2 H 4  l  + H 2 O  l 
2
H = – 143 kJ
1
H 2  g  + --- O 2  g   H 2 O  l 
2
H = – 286 kJ
2012 Chemistry — Paper Two — Question book
Question 4
“Hard” water is caused by the presence of calcium sulphate which has dissolved in water. This reacts
with soap [sodium stearate, CH3 (CH2 )1 6 COONa] to form the precipitate calcium stearate which is
the “hard water scum” deposit found in a bathtub.
A student adds 60 gallons of water at 45 °C to a large bathtub.
Assuming that the above water is “hard” due to it being saturated with calcium sulphate, what mass of
soap is required to just soften the water, i.e. remove all the calcium ions that are present?
•
•
•
•
1 gallon = 4.55 L
Ksp CaSO4 = 9.0  10– 6 at 45 °C
calcium stearate is completely insoluble at 45 °C
molecular weight of soap = 306 g.
Question 5
Nitric acid is manufactured by the Ostwald process.
In the first step, ammonia gas reacts with oxygen gas to produce nitric oxide in the presence of a
catalyst such as platinum with 10% rhodium. This reaction is carried out at a temperature of
approximately 900 °C and at a pressure of approximately 10 atmospheres.
4NH 3  g  + 5O 2  g 
4NO  g  + 6H 2 O  g  + heat
The nitric oxide is next oxidised at a temperature of approximately 50 °C and at high pressure.
2NO  g  + O 2  g 
2NO 2  g  + heat
The nitrogen dioxide then enters an absorption tower, where water is added through a fine spray
system in the presence of air to give nitric acid.
4NO 2  g  + O 2  g  + 2H 2 O  l 
4HNO 3  aq  + heat
Use your understanding of energy, rates of chemical reactions and chemical equilibrium to explain the
conditions used in the Ostwald process.
End of Paper Two
2012 Chemistry — Paper Two — Question book
3
4
2012 Chemistry — Paper Two — Question book
Very High Achievement
A high ability to use complex
reasoning in challenging
situations involving the
candidate’s understanding of
subject matter, and a high
ability to use scientific
processes at an advanced
level.
Criterion
Complex reasoning
processes
Sound Achievement
Some success in using
complex reasoning in
challenging situations
involving the candidate’s
understanding of subject
matter, and some success in
using scientific processes at
an advanced level.
High Achievement
Competence in using complex
reasoning in challenging
situations involving the
candidate’s understanding of
subject matter, and
competence in using scientific
processes at an advanced
level.
Paper Two
Limited Achievement
Very Limited Achievement
Assessment standards from the Chemistry Senior External Syllabus 1998
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