Tasmanian Certificate of Education - Home - TASCi)Predict the overall reaction using the half– equation technique. (2 marks) ... 10.0 kg block of magnesium will need replacing? Give

Questions: 2Pages: 7

©Copyright for part(s) of this examination may be held by individuals and/or organisations other than the Tasmanian

Secondary Assessment Board.

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Tasmanian Secondary Assessment Board

Tasmanian Certificate of Education

External Assessment

2000

CH856 CHEMISTRY

CRITERIA 2 AND 7

Time: 45 minutes

On the basis of your performance in this examination, the examiners will provide a rating of A, B, C orD on each of the following criteria taken from the syllabus statement:

Criterion 2 Communicate ideas and information using appropriate chemicallanguage and formats when undertaking chemical investigations.

Criterion 7 Demonstrate an understanding of the fundamental principles andtheories of electrochemistry.

CH856 Chemistry – Criteria 2 and 7

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CANDIDATE INSTRUCTIONS

Any two Chemistry texts are allowed to be used throughout the examination, however, the level andemphasis of treatment for syllabus topics and the chemical terminology used in the exam will bedetermined by the following two texts:

Elvins, et. al., Chemistry One – Materials Chemistry in Everyday Life (2nd ed.), Heinemann,1994.

Commons, et. al., Chemistry Two (3rd ed.), Heinemann, 1999.

Pages 234–247, plus page 254 (photocopied and backed) from Bucat, Elements of Chemistry, Volume1 may also be used throughout the examination.

No other printed material is allowed into the examination.

Answer ALL questions. 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 within each question so that the criteria can be assessed.

The quality and appropriateness of the presentation of your answers over the whole paper will be usedin arriving at an assessment for Criterion 2. Graphs, diagrams, the correct use of significant figuresand 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.

NOTE: 1 litre (L) = 1000 millilitres (mL) = 1dm3 = 1000 cm3.


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Question 1

(a) Copper metal is added to an acidified (1 mol L–1) aqueous solution of potassium dichromate.

(i) Predict the overall reaction using the half– equation technique. (2 marks)

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(ii) Does it necessarily mean that because you can write the balanced equation in part (i) abovethat the reaction will actually occur? Give reasons for your answer. (3 marks)

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(iii) Assume you wished to check the prediction in part (i) above, outline, using a fully labelleddiagram, an experimental method to test the prediction. What would you expect to observeif the predicted reaction occurred? (4 marks)

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Question 1 continues over the page.


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Question 1 (continued)

(b) Oil is transferred through underground iron pipes over long distances. To minimise corrosion ablock of magnesium is sometimes attached to the pipe, as shown below.

(i) What type of corrosion control does this involve? (1 mark)

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(ii) Write the two half–equations and the overall equation involved in this corrosion preventionsystem. (2 marks)

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(iii) On the diagram above, identify the cathode, the anode and the polarity of the magnesiumblock and iron pipe. Show the direction for the movement of electrons. (3 marks)

(iv) If this galvanic cell delivers a steady current of 200 mA, how long will it be before a10.0 kg block of magnesium will need replacing? Give your answer in years. (3 marks)

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(v) Theoretically, pure aluminium could also be used to prevent corrosion in this situation butis in practice not used. Explain this observation. (2 marks)

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Q1 Total Marks: /20

Iron pipe

Magnesium rod


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Question 2

The flow chart below shows the important sequence of events which occurs when a ‘lead-acid’ batteryis used to start a car engine.

(a) While the battery is being used to start the engine, what is the cathode half reaction? Indicatewhether this is an oxidation or reduction process. What is the change in oxidation state of thelead? (3 marks)

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(b) As the car engine operates, 14 volts of electricity is pushed back into the battery by the alternator.

(i) In terms of the battery, what is the name given to this process? (1 mark)

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(ii) If we assume the overall reaction occurring during this process is:

2PbSO4(s) + 2H2O(l ) → Pb(s) + PbO2(s) + 2SO4(aq)2– + 4H+

(aq)

What is the half cell reaction occurring at the negative terminal? (2 marks)

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Car Battery

Starter Motor

Car Engine

Car moves

Alternator

12V discharge14V recharge

Engine starts

Chemical energyconverted toelectrical energy.

Mechanicalenergy ofstarter motor.

Kinetic energy ofmoving car.

Mechanical energyconverted toelectrical energy.

Chemical energy inpetrol converted tomechanical energy.


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(iii) If 150 g of lead sulfate reacts, state what mass of lead oxide is deposited given:

M r(PbSO4) = 303g mol–1

M r(PbO2 ) = 239 g mol–1

(3 marks)

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(iv) Why is there an ‘apparent loss’ of lead in part (iii) above? How do you account for this?(2 marks)

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(c) Use the flow chart to suggest reasons why cars are most inefficient in the way they use energy.(3 marks)

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(d) Select a suitable reagent that under standard conditions will oxidise Pb(s) to Pb2 +(aq) but not

Cu(s) to Cu2+(aq) . What would be the E˚ of your cell? Use the electrochemical series in your

book. (2 marks)

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Question 2 continues opposite.


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(e) The diagram below shows an electrolysis cell where the electrolyte consists of a mixture of metalnitrates. Both electrodes are platinum (Pt).

(i) Using the electrochemical series, predict what reactions would occur at the cathode ifelectrolysis was continued for some time. (2 marks)

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(ii) After electrolysis had continued for some time, H2(g) was observed being produced at thecathode. Calculate how many coulombs of electricity pass through the cell before thisoccurs. (2 marks)

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Q2 Total Marks: /20

Pt Pt

+–

Aqueous solution containing:

0.10 mole Cu(NO3)20.05 mole AgNO30.05 mole Al(NO3)3




PLACE LABEL HERE



External Assessment

2000

CH856 CHEMISTRY

CRITERIA 2 AND 8

Time: 45 minutes



Criterion 8 Demonstrate an understanding of the principles and theories ofthermochemistry, rate of reaction and equilibrium.


Page 2














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Question 3

(a) Given the bond energies shown below, calculate the enthalpy change for the hydrogenation ofcyclohexene to cyclohexane. (4 marks)

C = C 607 kJ mol–1 C –C 343 kJ mol –1

H – H 436 kJ mol–1 C − H 410 kJ mol–1

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(b) Using the equation in part (a) above, explain the term ‘enthalpy’ of the reactants. (2 marks)

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(c) Is the reaction in part (a) above exothermic or endothermic? In terms of enthalpy change,explain your answer in part (a). (2 marks)

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C

H

CH

CH

HC

HH

C

CHHHH

Cyclohexene

+ H2(g)

C

H

CH

C HH

C

HH

C

CHHHH

Cyclohexane

H

H


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(d) (i) When finely ground platinum (Pt) was added to the hydrogenation reaction in part (a), itwas observed that the reaction occurred much faster, however, the enthalpy changeremained the same. Account for these two observations. An energy diagram will assistwith your answer. (4 marks)

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(ii) The same experiment was repeated using coiled platinum wire and the reaction rate wasobserved to be unchanged from the reaction in part (a). Account for this observation.

(3 marks)

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(e) (i) The reaction was observed to occur in the following steps:

Step 1: H2(g) 2H(g) ∆H1 = +437 kJ

Step 2:

Using the heat of reaction calculated in part (a), calculate the enthalpy change in Step 2.(2 marks)

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(ii) Briefly explain the thermochemical principle upon which the calculation in part (i) abovewas made. (3 marks)

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Q3 Total Marks: /20

Pt → catalyst

C

H

CH

CH

HC

HH

C

CHHHH

Cyclohexene

+ 2H(g)

C

H

CH

C HH

C

HH

C

CHHHH

Cyclohexane

H

H


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Question 4

(a) The reaction between H2(g) and I2(g) in a 1.0 litre container was observed to be:

H2(g) + I2(g) 2HI(g) ∆H negative

During the reaction the temperature was kept at 200˚C.

(i) Write an expression for the equilibrium constant, K, for this reaction. (1 mark)

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The concentration versus time graph for this reaction was determined and is shown below.

(ii) During which time intervals was the reaction at equilibrium? (2 marks)

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10 20 30 40 50 60

Point A Point B

Time (seconds)

Con

cent

rati

on (

mol

Lit

re–1

)

H2

I2

A B

0.120

0.110

0.100

0.090

0.080

0.070

0.060

0.050

0.040

0.030

0.020

0.010

0

HI


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(iii) Using the first equilibrium position, calculate the value of ‘K’, the equilibrium constant,for this temperature. (2 marks)

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(iv) At Point A a sudden change occurred. What happened at this point? (2 marks)

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(v) What happened between Point A and Point B? Use Le Chatelier’s principle to help withyour answer. (3 marks)

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(vi) If an increase in temperature had occurred in the system while it was at equilibrium, predictand explain the effect of the change on the concentration of each substance present.

(3 marks)

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(vii) If the volume of the container was halved at Point B, predict and explain the outcome foreach species present. (2 marks)

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(b) The Australian Government is investigating the commercial production of an alternative car fuelcalled ‘Gasohol’. This is said to be ‘cleaner’ because it is a mixture of 10% ethanol and 90%by volume unleaded petrol. Unleaded petrol has a heat of combustion of 34.2 kJ mL–1 andethanol 23.4 kJ mL–1 .

(i) Calculate the heat of combustion of ‘Gasohol’. (2 marks)

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(ii) For a car that needs 8.00 litres of unleaded petrol to travel 100 km, how many litres of‘Gasohol’ would be needed to travel the same distance under the same conditions andassuming the same efficiency? (3 marks)

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Q4 Total Marks: /20




PLACE LABEL HERE



External Assessment

2000

CH856 CHEMISTRY

CRITERIA 2 AND 9

Time: 45 minutes



Criterion 9 Demonstrate an understanding of properties and reactions of inorganicand organic matter.


Page 2














Page 3

Question 5

(a) Give systematic names for the following:

(i) (1 mark)

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(ii) (1 mark)

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(iii) (1 mark)

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(iv) (1 mark)

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(b) Draw structural formulae for:

(i) 1,2–dichlorobutanal; (1 mark)

(ii) 2–methylpropanoic acid; (1 mark)

(iii) 3–ethylpentan–3-ol; (1 mark)

(iv) hexylethanoate. (1 mark)


CCH 2CH 2

O

O CH 2 CH 2CH 2 CH 3

CH 3

CCH 3

O

CH 3

C OHCH3

CH3

CH3

CH 3 CHCH CH 2 OH

Br Br


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(c) An organic acid (X) has an empirical formula of CH2O.

(i) Give a possible molecular formula and structural formula for the compound. (2 marks)

(ii) Write the structural formula and systematic name of one isomer of X. (2 marks)



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(d) A pure organic compound (A) has a molecular formula of C4H10O. On analysis, compound Ahas the following properties:

• it is oxidised by acidified permanganate solutions producing a non-acidic product (B) ofmolecular formula C4H8O;

• it reacts with Na (s) producing a flammable gas.

(i) Deduce the structures and names of compound A and product B. Explain your reasoning.(5 marks)

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(ii) Write a balanced equation for the reaction of compound A with an acidified permanganatesolution (MnO4

– /H +). Do not use structural formulae. Molecular formulae forcompound A and product B are sufficient. (3 marks)

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Q5 Total Marks: /20


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Question 6

(a) A sealed balloon containing argon gas (atomic mass = 40) will sink to the floor if released in aroom with no air movements. If the balloon is ‘popped’ and the argon gas escapes into theroom, it can be detected in equal concentrations throughout the room after a certain period oftime.

(i) Explain why the argon filled balloon sinks. (2 marks)

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(ii) Explain why the escaped argon distributes itself evenly throughout the room. (2 marks)

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(b) The elements in the periodic table rarely have relative atomic masses that are whole numbers.For example, Zn is 65.4. Explain this observation. (2 marks)

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(c) Ammonia gas, NH3(g) , and nitric acid, HNO3(aq) , are used to produce the important industrialand agricultural chemical ammonium nitrate.

(i) Write an equation for the reaction that occurs. (1 mark)

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(ii) Is ammonium nitrate a covalent compound or an ionic compound? Justify your answer.(2 marks)

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(d) (i) Write a balanced equation for the reaction of fluorine gas and potassium metal. (1 mark)

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(ii) Explain the difference between the type of bond present in a molecule of fluorine and thetype of bond present in the product of the reaction in part (i) above. Use diagrams to helpexplain your answer. (4 marks)

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(e) (i) Write down the electronic configurations of elements F, Ne and Na. (3 marks)

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(ii) Which of these elements would have the highest first ionisation energy? Justify youranswer. (3 marks)

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Q6 Total Marks: /20




PLACE LABEL HERE



External Assessment

2000

CH856 CHEMISTRY

CRITERIA 2 AND 10

Time: 45 minutes



Criterion 10 Apply logical processes to solve quantitative chemical problems.


Page 2














Page 3

Question 7

(a) The molecular formula of ascorbic acid (Vitamin C) is C6H8O6 .

(i) Nutritionists recommend a minimum daily intake of Vitamin C of 15 mg. Calculate thenumber of mole of Vitamin C in this amount. (2 marks)

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(ii) A sample of orange juice contains 30 mg of Vitamin C in every 100 mL. Calculate theconcentration of Vitamin C in mol L–1 . Express your answer to two significant figures.

(2 marks)

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(b) During the extraction of gold (Au) from gold containing ores, it is dissolved by reaction withcyanide ions (CN – ) and oxygen (O2 ) according to the following equation:

4Au(s) + 8CN(aq)– + 2H2O(l ) + O2(g) → 4Au(CN)2(aq)

– + 4OH–(aq)

(i) Calculate the mass of Au(s) that could, in theory, react with 100 L of a 0.750 mol L–1

cyanide solution given Ar(Au) = 197 g mol –1 . (2 marks)

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(ii) An accident occurred where 100 L of a 0.750 mol L–1 cyanide solution leaked into aholding pond containing 9900 L of a 6.44 ×10–3 mol L–1 cyanide solution. Calculate thenew concentration of cyanide in the holding pond after the leak occurred. (4 marks)

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(c) The contents of a laboratory reagent bottle containing solid potassium hydroxide, KOH(s) , hasbeen contaminated by moisture. You have been given the job of determining the extent ofcontamination. This is to be done by titrating a solution of this KOH with a standardisedhydrochloric acid solution (HCl) of pH 1.14. You are to use the following procedure:

Step 1: Dissolve 2.80 g of the contaminated KOH(s) into 500.0 mL of solution.

Step 2: Fill a burette with this solution and use it to titrate a 20.00 mL sample of the HCl (aq)using a suitable indicator.

Step 3: Repeat the titrations until a consistent end point is obtained.

After completing the titrations, the following data is available:

• Titration end point = 15.80 mL of KOH(aq) .• pH of HCl (aq) = 1.14.

• Titration reaction is H+

(aq) + OH–(aq) → H2O(l) .

To find the extent of contamination of the KOH(s) , calculate the following:

(i) the concentration of H+(aq) in the HCl (aq) ; (2 marks)

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(ii) the number of moles of H+(aq) used in each titration; (2 marks)

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(iii) the concentration of OH– in the KOH(aq) solution; (2 marks)

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(iv) the mass of KOH(s) in the 500.0 mL of solution originally prepared; (2 marks)

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(v) the percentage by mass of moisture in the contaminated KOH(s) . (2 marks)

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Q7 Total Marks: /20


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Question 8

(a) 6.60 g of dry ice, CO2(s) , is placed inside an empty balloon which is then sealed. Calculate thevolume that the balloon will eventually reach if all the dry ice turns into CO2(g) at a temperature

of 27.0˚C and a pressure of 125 kPa, given M(CO2 ) = 44.0 g mol –1 . (3 marks)

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(b) Calculate the number of atoms of He (g) that are needed to exert a pressure of 4.0 ×10–2

kPa in a 15 mL container at a temperature of –23˚C. (4 marks)

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(c) Butane gas, C4H10(g), burns in O2(g) to produce CO2(g) , H2O(g) and energy.

(i) Write a balanced equation for the reaction. (1 mark)

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(ii) Calculate the volume of O2(g) needed at STP conditions to react with 5.80 kg of butane

given M(C4H10) = 58.0 g mol –1. Give your answer to the correct number of significant

figures. (4 marks)

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(iii) What mass of CO2(g) would be produced by the burning of 5.80 kg of butane?(2 marks)

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(iv) The energy released by the burning of butane is quoted as 0.124 MJ L–1

at STP.

Calculate the energy released in units of MJ kg–1. (4 marks)

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(v) Calculate the energy released when 5.80 kg of butane is burnt. Express your answer inkilojoules (kJ). (2 marks)

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Q8 Total Marks: /20

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Tasmanian Certificate of Education - Home - TASCi)Predict the overall reaction using the half– equation technique. (2 marks) ... 10.0 kg block of magnesium will need replacing? Give