Download PLACE LABEL HERE Tasmanian Certificate of Education

PLACE
LABEL
HERE
Tasmanian Secondary Assessment Board
Tasmanian Certificate of Education
External Assessment
1999
CH856 CHEMISTRY
Time: Three Hours
On the basis of your performance in this examination, the examiners will provide a rating of A, B, C or
D on each of the following criteria taken from the syllabus statement:
Criterion 2
Communicate ideas and information using appropriate chemical
language and formats when undertaking chemical investigations.
Criterion 7
Demonstrate an understanding of the fundamental principles and
theories of electrochemistry.
Criterion 8
Demonstrate an understanding of the principles and theories of
thermochemistry, rate of reaction and equilibrium.
Criterion 9
Demonstrate an understanding of properties and reactions of inorganic
and organic matter.
Criterion 10
Apply logical processes to solve quantitative chemical problems.
Pages:
Questions:
©
51
8
Copyright for part(s) of this examination may be held by individuals and/or organisations other than the Tasmanian
Secondary Assessment Board.
CH856 Chemistry
CANDIDATE INSTRUCTIONS
Any two Chemistry texts are allowed to be used throughout the examination, however, the level and
emphasis of treatment for syllabus topics and the chemical terminology used in the exam will be
determined by the following two texts:
Elvins, et. al., Chemistry One – Materials Chemistry in Everyday Life (2nd ed.), VCE
Heinemann, 1995.
Commons, et. al., Chemistry Two – Chemistry and the Marketplace, Energy and Matter (2nd
ed.), VCE Heinemann, 1995.
Pages 234 – 247, plus page 254 (photocopied and unannotated) from Bucat, Elements of Chemistry,
Volume 1 may also be used throughout the examination.
No other printed material will be allowed into the examination.
An electronic calculator may be used.
The examination consists of eight questions which are organised around the criteria 7, 8, 9 and 10.
All questions should be answered. Answers must be written in the spaces provided on the examination
paper.
Each question is of equal value and should take about 22 minutes.
You should make sure you answer all parts from each question so that all criteria can be assessed.
The quality and appropriateness of the presentation of your answers over the whole paper will be used
in arriving at an assessment for Criterion 2. Graphs, diagrams, the correct use of significant figures
and English expression are important for this purpose.
No credit can be given for incorrect answers unless they are accompanied by details of the working.
Some credit will be given for unsimplified answers. Appropriate units must be included.
Blank pages are included on each left hand page. If you wish anything from these pages to be marked
please indicate clearly by writing ‘PLEASE MARK’.
NOTE: 1 litre (L) = 1000 millilitres (mL) = 1dm3 = 1000 cm3.
Page 3
CH856 Chemistry
Question 1 — This question assesses Criterion 2 and Criterion 10.
(a)
(i)
Calculate the mass of K 2SO 4(s) needed to make 1.00 L of an aqueous solution with a
potassium ion concentration of 0.400 mol L–1 . M(K 2 SO 4 ) = 174 g mol –1 .
(2 marks)
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(ii)
Calculate the mass in milligrams (mg) of potassium ions contained in 1 drop (0.0500 mL)
of the solution in part (a) above.
(3 marks)
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(b)
When the K 2SO 4(aq) solution from part (a) above is added to industrial waste water containing
Ba 2 +(aq) , insoluble barium sulfate precipitates.
(i)
If 0.0680 g of barium sulfate is precipitated from 10.00 mL of waste water when treated
with an excess of K 2SO 4(aq) , calculate the concentration of Ba 2 +(aq) ions in the waste
water. M(BaSO 4 ) = 233 g mol –1 .
(3 marks)
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(ii)
Calculate the minimum volume of the K 2SO 4(aq) solution that is needed to precipitate out
all of the Ba 2 +(aq) from 10.00 mL of waste water.
(3 marks)
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Page 5
CH856 Chemistry
Question 1 (continued)
(c)
Calculate the pH of each of the following:
(i)
a solution made by dissolving 0.01000 mol of HCl (g) in enough water to make 100.0 mL
of solution;
(1 mark)
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(ii)
a solution made by diluting 250 mL of HNO3(aq) of pH 2.00 to 500 mL with water.
(2 marks)
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(d)
Calculate the concentration of OH – (aq) ions in a sodium hydroxide solution (NaOH (aq) ) of pH
13.0.
(2 marks)
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Page 7
CH856 Chemistry
Question 1 (continued)
(e)
A solution of 0.400 mol L–1 H2 SO 4(aq) is titrated into 20.0 mL of 0.600 mol L–1 KOH(aq) .
Write a balanced equation for the titration reaction and calculate the concentration of H +(aq) ions
in the titration solution after 10.0 mL of H2 SO 4(aq) has been titrated into the KOH(aq) solution.
(4 marks)
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Q1 Total marks ............./20
(Criterion 10)
Page 9
CH856 Chemistry
Question 2 — This question assesses Criterion 2 and Criterion 10.
(a)
What are Standard Laboratory Conditions, SLC, if pressure was stated in kilopascals (kPa) and
temperature was stated in Kelvin (K)?
(2 marks)
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(b)
(i)
A sample of gas stored at SLC occupies a volume of 750.0 mL. Calculate the volume that
this gas would occupy if the pressure was increased to 303.9 kPa and the temperature
decreased to 223.5 K.
(3 marks)
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(ii)
Calculate the number of moles of gas in the sample in part (i) above.
(3 marks)
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Page 11
CH856 Chemistry
Question 2 (continued)
(c)
An LPG gas cylinder contains 10.0 kg of propane.
(i)
Calculate the volume of air required to supply enough oxygen gas to completely burn the
propane.
The following information can be used to help answer this question:
• Balanced equation for combustion of propane is:
C3 H8(g) + 5O2(g) → 3CO2(g) + 4H2 O(g)
• Air temperature is 11.0˚C.
• Air pressure is 102 kPa.
• 20.9% of air, by volume, is oxygen gas.
(8 marks)
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Question 2 continues over the page.
Page 13
CH856 Chemistry
Question 2 (continued)
(ii)
In part (c) (i) it is assumed that all the propane in the cylinder is available for burning. In
reality, this is not the case. Explain this fact. Comment on whether this fact will
significantly change the volume of air required in part (c) (i).
(4 marks)
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Q2 Total marks ............./20
(Criterion 10)
Page 15
CH856 Chemistry
Question 3 — This question assesses Criterion 2 and Criterion 9.
(a)
Draw structural formulae for:
(i)
2–methylpropanal;
(1 mark)
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(ii)
butanoic acid;
(1 mark)
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(iii) 2,2–dimethylbutan–1–ol;
(1 mark)
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(iv)
pentylmethanoate;
(1 mark)
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(b)
Give systematic names for the following:
(i)
CH 3
CH 2
CH 2
CH 2
OH
(1 mark)
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(ii)
O
CH 3
C
O
CH 2
CH 3
(1 mark)
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(iii) CH 3
O
CH
C
OH
CH 3
(1 mark)
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(iv)
Cl
Cl
C
O
C
H
Cl
(1 mark)
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Question 3 continues over the page.
Page 17
CH856 Chemistry
Question 3 (continued)
(c)
An organic compound, X, has an empirical formula of CH2 O . Laboratory tests show that:
•
•
an aqueous solution of X is acidic;
X will not react with an acidified permanganate solution; and
•
H2(g) is released when Mg(s) is added to X(aq) .
(i)
Deduce the structural formula of X. Give its systematic name and explain your reasoning.
(4 marks)
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(ii)
Write a balanced equation for the reaction of X(aq) with Mg(s) .
formula of X in your equation.
Use the molecular
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Page 19
CH856 Chemistry
Question 3 (continued)
(d)
A non-acidic organic compound has a molecular formula of C 4 H8O2 and has a single functional
group.
(i)
What is the name of the functional group in this compound?
(1 mark)
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(ii)
Draw the structural formulae of two different isomers that fit this molecular formula.
(2 marks)
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(iii) Select one of your isomers in part (ii) above. Write a balanced equation to show how this
isomer could be produced in the laboratory. Include in your answer:
•
•
structural formulae and names of all organic compounds involved;
the name of a suitable catalyst.
(3 marks)
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Q3 Total marks ............./20
(Criterion 9)
Page 21
CH856 Chemistry
Question 4 — This question assesses Criterion 2 and Criterion 9.
(a)
A sealed container of ‘rotten egg’ gas, H2 S(g) is opened inside a room with no ventilation or air
movements. It only takes a few minutes for the smell of the H2 S(g) to be detected anywhere
inside the room. Explain how this is possible.
(2 marks)
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(b)
During the manufacture of sulfuric acid an accident occurred which caused a large volume of
SO 2(g) to escape into the atmosphere.
(i)
Explain why this accident would contribute to an acidification of the local atmosphere
around the sulfuric acid plant. Use a chemical equation to help explain your answer.
(2 marks)
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(ii)
Why should workers and nearby residents be concerned about the possible effects the
escaped SO 2(g) might have?
(2 marks)
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Question 4 continues over the page.
Page 23
CH856 Chemistry
Question 4 (continued)
(c)
A halogen (X2 ) in Period 2 of the periodic table is allowed to react with an alkali metal (Y) in
Period 4.
(i)
Write down the symbol and electronic configuration of the elements X and Y.
(2 marks)
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(ii)
Write down the chemical formula of the product of the reaction. State the type of bonding
present in the product.
(2 marks)
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(iii) Which element, X or Y, would have the lower first ionisation energy? Justify your answer.
(2 marks)
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(iv)
The alkali metal (Y) reacts readily with a non-metal (Z). The compound formed has a
molecular mass of approximately 94 and forms a basic solution when dissolved in water.
Identify Z, giving reasons for your choice. Write down the formula of the compound
formed.
(4 marks)
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(d)
F – , Ne and Na + are isoelectronic (ie. contain the same number of electrons) but have radii that
vary significantly. Which one has the largest radius? Justify your answer.
(2 marks)
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Question 4 continues over the page.
Page 25
CH856 Chemistry
Question 4 (continued)
(e)
Na + ions are commonly found in compounds containing sodium but Na 2+ ions are unknown
in compounds. Explain why.
(2 marks)
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Q4 Total marks ............./20
(Criterion 9)
Page 27
CH856 Chemistry
Question 5 — This question assesses Criterion 2 and Criterion 8.
(a)
Bushwalkers commonly use methylated spirits as a source of fuel. Assume methylated spirits to
be principally ethanol and that the combustion reaction is as shown below.
CH3 CH2 OH(g) + 3O2(g) → 2CO2(g) + 3H2 O(g)
(i)
Using the bond energies given, calculate the heat of reaction in kJ mol –1 for the complete
combustion of ethanol.
(4 marks)
C–C
C–H
C–O
O–H
C=O
O=O
348
413
357
462
744
498
kJ
kJ
kJ
kJ
kJ
kJ
mol –1
mol –1
mol –1
mol –1
mol –1
mol –1
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(ii)
Ethanol is a good source of energy. Explain this in terms of the enthalpy of reactants and
products.
(4 marks)
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Page 29
CH856 Chemistry
Question 5 (continued)
(iii) Bushwalkers carry the methylated spirits (ethanol) in a container where it is constantly
exposed to air (oxygen). Using appropriate diagrams and discussion, explain why the
methylated spirits does not spontaneously combust or burn in the container.
(4 marks)
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(b)
Ethanol in wine will oxidise very slowly to ethanoic acid in the presence of oxygen. This makes
the wine more sour (acidic).
O
CH3 CH2 OH( l) 2 →CH3 CO OH(aq) very slowly
However, if the wine is stored in vessels containing any copper, Cu(s) , the rate of this reaction is
greater and the wine spoils more quickly.
Cu
( s)
CH3 CH 2 OH (l)  

→ CH 3 CO OH(aq) more quickly
O
2
(i)
How would you describe the role of Cu(s) in this oxidation reaction?
(1 mark)
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(ii)
Use an energy diagram to help explain this observation. What effect does Cu(s) have on
the heat of reaction for this oxidation reaction?
(4 marks)
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Question 5 continues over the page.
Page 31
CH856 Chemistry
Question 5 (continued)
(c)
What mass in kilograms of propane gas must be burnt to yield 100 MJ of heat energy?
(1 MJ = 10 6 Joules) Assume the propane is completely combusted.
(3 marks)
C3 H8(g) + 5O2(g) → 3CO2(g) + 4H2 O(g)
∆H = –2220 kJ
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Q5 Total marks ............./20
(Criterion 7)
Page 33
CH856 Chemistry
Question 6 — This question assesses Criterion 2 and Criterion 8.
(a)
Consider the following equation at equilibrium:
PbCl 2 (s)
(i)
Pb2+ (aq) + 2Cl – (aq)
∆H is positive
Write an expression for K, the equilibrium constant.
(1 mark)
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(ii)
What information does the magnitude of ‘K’ indicate?
(1 mark)
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(iii) The concentration of the solids in an equilibrium is usually assigned as ‘l’. How can this
be justified?
(2 marks)
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(iv)
If the temperature was increased, explain the impact on the equilibrium constant and the
concentration of Pb2 +(aq) .
(3 marks)
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Page 35
CH856 Chemistry
Question 6 (continued)
(b)
Methanoic acid and hydrochloric acid both react with water to form ions:
HCOOH(aq) + H 2O( l)
HCl (aq) + H2 O
H3 O+(aq) + HCOO– (aq)
H3 O+(aq) + Cl – (aq)
The pH of the solutions prepared by dissolving 1 mole of each of hydrochloric acid and
methanoic acid in 1 L of water is given below:
pH of HCOOH is 1.9
pH of HCl is 0
(i)
What is the concentration of H3 O+ in the 1 mol L–1 methanoic acid?
(1 mark)
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(ii)
Why are the pH of the two acid solutions different even though the initial concentrations
of the acids are the same?
(3 marks)
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Page 37
CH856 Chemistry
Question 6 (continued)
(c)
Bromthymol blue, BTB, is an indicator for acid base titrations whose equilibrium is represented
by:
H – Bromthymol blue (aq)
H +(aq) + Bromthymol blue – (aq)
(yellow)
(blue)
or
H – BTB(aq)
(i)
H +(aq) + BTB – (aq)
Write an expression for the equilibrium constant.
K = 10 –7 at 25˚C
(1 mark)
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(ii)
If two drops of indicator were added to a solution at pH 5, what would be the ratio of
[BTB– (aq) ]
?
(3 marks)
[H – BTB(aq) ]
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(iii) What is the significance of this ratio in terms of the relative amounts of BTB – (aq) and
H – BTB(aq) ? What would be the colour of the solution?
(2 marks)
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(iv)
How would the ratio of BTB – (aq) to H – BTB(aq) change if the pH of the solution is
increased from 5 to 8? Explain your answer.
(3 marks)
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Q6 Total marks ............./20
(Criterion 7)
Page 39
CH856 Chemistry
Question 7 — This question assesses Criterion 2 and Criterion 7.
(a)
The vanadium battery is being developed as an alternative to the lead/acid rechargeable battery
for use in electric vehicles. As a vanadium battery discharges the unbalanced, overall reaction is:
VO +2(aq) + V2+ (aq) → VO 2+ (aq) + V3+ (aq)
(i)
What is meant by the term ‘rechargeable battery’?
(1 mark)
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(ii)
What is the oxidation state of the vanadium in each of the species shown in this equation?
(2 marks)
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(iii) Using the half equation technique, balance the overall equation shown. Show all
equations.
(3 marks)
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(iv)
While the cell is recharging identify the anode half equation.
(2 marks)
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Question 7 continues over the page.
Page 41
CH856 Chemistry
Question 7 (continued)
(b)
Heart pacemakers may operate by using a special type of electrochemical cell (biogalvanic)
where zinc, Zn (s) and platinum, Pt (s) , electrodes are implanted into body tissue. The Zn (s)
electrode undergoes oxidation, while at the Pt (s) electrode oxygen in the body tissues is reduced
according to the half equation:
O2(g) + 2H2 O(l ) + 4e – → 4OH – (aq)
(i)
E° = +0.40 volt
Write a balanced overall equation for the chemical reaction that occurs as the cell is
discharging. Label ‘anode’ and ‘cathode’ half equations.
(3 marks)
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(ii)
Assuming standard laboratory conditions, what would be the initial voltage of the cell
given that E° = –0.76 V for the zinc reduction half equation.
(2 marks)
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(iii) If the cell produces a steady current of 40 microamp (4.00 × 10 –5 amp) calculate the time
it will take before a zinc electrode of mass 4.101 g needs replacing. Express your answer
in years.
(4 marks)
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Question 7 continues over the page.
Page 43
CH856 Chemistry
Question 7 (continued)
(iv)
Silver has been suggested as a replacement for zinc in the heart pacemaker. Use your
knowledge of E° values to comment on whether silver is an appropriate alternative.
(3 marks)
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Q7 Total marks ............./20
(Criterion 8)
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CH856 Chemistry
Question 8 — This question assesses Criterion 2 and Criterion 7.
(a)
The metal tin, Sn(s) , is often used to surface coat steel cans to protect them from corrosion.
(i)
In terms of the mechanisms of corrosion, explain how this protective coating works.
(3 marks)
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(ii)
Once the coating is scratched and the steel is exposed, corrosion actually occurs more
rapidly than if the tin were not there. In terms of corrosion mechanisms, explain why this
occurs.
(4 marks)
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(b)
A second alternative for the protection of steel from corrosion is to galvanise with zinc. Give a
chemical reason, with equation, why Zn galvanising is not used to protect steel food cans from
corrosion.
(3 marks)
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Question 8 continues over the page.
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CH856 Chemistry
Question 8 (continued)
(c)
People searching for silver coins and jewellery at the bottom of the sea usually find them coated
with the corrosion product silver sulfide, Ag2 S(s) , a black solid. To restore the silver coins
‘cathodic reduction’ is used. A possible cell for this process is shown in the diagram below.
Recovery of Corroded Silver Coins
Power Supply
+
–
Copper Bar
5% NaOH(aq)
Stainless Steel Bar (Anode)
Corroded Silver Coins (Cathode)
At the cathode: Ag2 S(s) + 2e – → 2Ag(s) + S2– (aq)
At the anode: 4OH – (aq) → O2(g) + H2 Ol + 4e –
(i)
Mark on the diagram the direction of flow of electrons and the direction of flow of ions
in solution.
(2 marks)
(ii)
Write a net ionic equation for this reaction.
(2 marks)
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(iii) At the cathode a few bubbles of gas may also be seen. Suggest what this gas might be and
account for its presence in terms of the appropriate half equation.
(2 marks)
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Question 8 continues over the page.
Page 49
CH856 Chemistry
Question 8 (continued)
These recovered silver coins will re-tarnish (Ag2 S(s) reforms) when exposed to the air of
industrialised cities.
(iv)
Why is re-tarnishing more likely in industrialised cities?
(2 marks)
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(v)
A thin electroplated coating of the metal rhodium onto the surface will protect the silver
from tarnish. Give a reason why a thin coating of rhodium protects the coins from retarnishing.
(2 marks)
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Q8 Total marks ............./20
(Criterion 8)
Page 51