Past Paper_fossil Fuels And Carbon Compounds

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds

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Part 8: Fossil Fuels and Carbon Compounds 1.

The following flow diagram shows the conversion of ethene to an acid Y. ethene

ethanol

Y

Ethene can rapidly decolorize a solution of bromine in 1,1,1-trichloroethane. (a)

Write a chemical equation for the reaction between ethene and bromine.

(b)

(i)

Give the systematic name of Y.

(ii)

Draw a labelled diagram of the laboratory set-up for the conversion of ethanol to Y.

(c)

Ethanol can be detected in the breath of a drunken driver. Suggest ONE chemical test to show the presence of ethanol in his breath and state the observable change produced by the test.

(7 marks) [modified 1995-CE-7b]

2.

The relative molecular mass of an alkanol X is 60.0. X contains 60% of carbon by mass. (a)

Calculate the number of moles of carbon in one mole of X and hence deduce the molecular formula of X.

(b)

Draw ONE possible structure of X and give its systematic name.

(5 marks) [1996-CE-2]

3.

The photograph below shows a gas burner with a can of fuel. The can contains 250 g of liquefied butane.

(a)

Write the structural formula of butane.

(b)

(i)

Write the chemical equation for the complete combustion of butane.

(ii)

Suggest a chemical test for EACH of the products formed when butane is completely burnt in air.

(iii)

Calculate the volume of the gaseous product formed, measured at room temperature and pressure, if all the butane contained in the can is completely burnt in air.

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds (c)

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Explain why it is dangerous to use such gas burners in a poorly-ventilated room.

(Molar volume of gas at room temperature and pressure = 24.0 dm3)

(9 marks) [1997-CE-9a]

4.

The teacher used ethanol solution) to carry out the following experiment on a redox reaction:

(a) (i)

State the observable change in the test tube.

(ii)

Explain, in terms of oxidation number, whether potassium dichromate was oxidized or reduced.

(iii)

Give the structural formula of the product formed from ethanol in the reaction.

(b) Suggest ONE reason for each of the following statements: (i)

Drinking a small quantity of wine may be good for health.

(ii)

Excessive drinking of alcoholic beverages may cause health problems.

(7 marks) [1999-CE-6b]

5. Cracking of naphtha gives alkane X (relative molecular mass 44), alkene Y (relative molecular mass 42) and other products. (a) What is the meaning of the term ‘cracking’? (b) Suggest a chemical test to distinguish between X and Y. (c) Deduce the molecular formula of Y. (d) Y can be used as a starting material for the production of plastic Z.

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds (i)

Write the chemical equation for the formation of Z from Y.

(ii)

Suggest how plastic cups can be made from Z.

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(e) Suggest an advantage and a disadvantage of using plastic wastes as an energy source. (10 marks) [1999-CE-9b]

6.

The diagram below shows a burning candle:

(a)

The candle wax is a petroleum product. What type of compounds is mainly present in the wax?

(b)

(i)

In which of the following states does wax act as the fuel in a burning candle? Solid, liquid, vapour

(ii) (c)

State the conditions required for the combustion of wax.

Explain why it is hazardous to add cold water to a tray containing molten wax at a high temperature. (6 marks) [2001-CE-1]

7.

Using alkenes as an example, describe the characteristics of members of a homologous series

.

(9 marks) [2002-CE-5]

8.

Ethyl ethanoate is an ester. It can be prepared by heating a mixture of ethanoic acid and ethanol under reflux in the presence of a catalyst.

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds

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(a)

What is the catalyst used in the preparation?

(b)

Draw a labelled diagram of the set-up used for heating the mixture under reflux.

(v)

Which ONE of following hazard warning labels should be displayed on a bottle of ethyl ethanoate?

(d)

Draw the structure of another ester which has the same molecular formula as ethyl ethanoate, and give its systematic name.

(9 marks) [2002-CE-6c]

9.

Sulphur dioxide is formed when coal is burnt in a power station. (a) The coal used in the power station contains 1.5% of sulphur by the mass. Calculate the volume of sulphur dioxide released, measured at room temperature and pressure, when 1.0 kg of the coal is burnt. (You may assume that all the sulphur in coal is converted to sulphur dioxide upon burning.) (b) State ONE environmental problem associated with the emission of sulphur dioxide into the atmosphere. (c) Suggest ONE measure to reduce the emission of sulphur dioxide from the power station. (d) Particulates are also present in the flue gas generated in the power station. (i)

State ONE environmental problem associated with the discharge of particulates into the atmosphere.

(ii) Suggest ONE way to remove particulates from the flue gas. (Relative atomic masses : O = 16.0, S = 32.0; molar volume of gas at room temperature and pressure = 24 dm3) (7 marks)

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds

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10.

Organic wastes can be used as an alternative energy source. Under suitable conditions, the wastes can be digested by bacteria to give a gaseous mixture containing a high proportion of methane. Methane can be used as fuel. (a)

Suggest ONE organic waste that can be used for this purpose.

(b)

Write the chemical equation for the complete combustion of methane.

(c)

Suggest ONE advantage of using organic wastes as an alternative energy source.

(d)

Suggest ONE reason why organic wastes are not yet widely used as an energy source. (4 marks) [2003-CE]

11.

A policeman suspected a car driver to have drunk an excessive amount of alcoholic drinks, and used a dichromate breathalyser to conduct a test on the driver’s breath. The result was positive. (a)

State the principle underlying the test of ethanol using a dichromate breathalyser.

(b)

The driver claimed that he had just rinsed his mouth using ethanol-containing mouthwash. Without using other instruments, suggest how the policeman could check whether the driver’s claim was valid or not. Explain your answer.

(4 marks)

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds

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[2004-CE-8c]

12. An ester can be prepared by heating an alkanol with an alkanoic acid under reflux in the presence of concentrated sulphuric acid. (a)

Draw a labelled diagram to show the set-up used in heating the reaction mixture under reflux.

(b)

Suggest ONE reason why it is necessary to heat the mixture under reflux.

(3 marks) [2004-CE-9b]

13.

Both ethane and ethene are hydrocarbons. Compare the chemical reactions of these two hydrocarbons with reference to their structures.

14.

(9 marks) [2005-CE-S-9]

Both pentane (C5H12) and octane (C8H18) are members of the same homologous series. (a)

Using pentane and octane as examples, illustrate TWO characteristics of the members of a homologous

series.

(4 marks)

(b)

Which compound, pentane or octane, will burn with a more sooty flame? Explain your answer.

(c) Draw TWO structures which have the same molecular formula C5H12.

(2 marks) (2 marks) [2005-CE-5]

Ans: 1.

(a)

CH2=CH2 + Br2  CH2BrCH2Br

1

(b)

(i)

Ethanoic acid

1

(ii)

Diagram of heating under reflux

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds

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If more than 1 diagram is drawn, only the first diagram will be marked.)

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deduct 1 mark for worng reagents/ incomplete indication of reagents deduct 1 mark for closed / open system deduct 1 mark for wrong / no indication of direction of water flow deduct 1 mark for no indication of heat (max mark deducted =3) (c)

2.

(a)

pass the breath into acidified potassium dichromate solution.

1

The colour of the solution will change from orange to green.

1

1 mole of X contains

60.0 × 0.6 12

1 mark for method

= 3 moles of C The general formula of alkanol is CnH2n+1OH (CnH2n+2O) / alkanol possesses an alkyl group and a hydroxyl

(b)

3.

group.

1

∴ molecular formula of X is C3H7OH (C3H8O)

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CH3CH2CH2OH : propan-1-ol

1+1

Or (CH3)2CHOH : propan-2-ol

1+1

(a)

CH3CH2CH2CH3 / structural formula

(b)

(i)

2C4H10 + 13O2  8CO2 + 10H2O or C4H10 +

(ii)

1 1

1 6 O2  4CO2 + 4H2O 2

(1)

carbon dioxide can turn lime water milky

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water can turn anhydrous copper(II) sulphate from white to blue / anhydrous cobalt(II) chloride (paper) from blue to pink (iii)

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relative molecular mass of butane = 12 x 4 + 1 x 10 = 58 no. of moles of butane in the can = 250 / 58 = 4.31

1 (method)

Upon complete combustion, 1 mole of butane produces 4 moles of carbon dioxide Volume of gas produced = 4 x 250 / 58 x 24.0 dm3 = 414 dm

1 (method)

3

1

(Accept answer from 412 to 414 dm3; deduct 1 mark for wrong/ no unit) (c)

Incomplete combustion of butane may occur which produces carbon monoxide/ CO which is toxic/ poisonous.

4.

(a)

(i)

acidified potassium dichromate solution changes from orange to green

(ii)

O.N. of Cr in Cr2O72- is +6 / VI

1,1

1

O.N. of Cr in Cr3+ is +3 / III

1

Cr2O72- is reduced because O.N. of Cr decreases

1

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds (iii)

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CH3CO2H or structural formula

1

(also accept structural formula of ethanal, CH2CHO) (b)

(i)

drinking a small quantity of wine can reduce the proneness to heart attack.

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(Also accept causing thinning of blood.) (ii)

Excessive drinking can cause brain damage/ depression/ hepatitis/ cirrhosis of the liver / stomach ulcer/ cancer of mouth, throat and gullet.

5.

(a)

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Breaking down of large hydrocarbon (molecules) to small hydrocarbon (molecules) by heat with the help of a catalyst

1

or Breaking down of heavy petroleum fractions(long chain carbon compounds) into light petroleum fractions (short chain carbon compounds)

(1)

(Accept equivalent answers.) (b)

Treat compounds with bromine in 1,1,1-trichloroethane/ bromine water.

1

Y can cause the bromine solution to change from brown/ orange to colourless rapidly

1

Or Treat compounds with acidified KMnO4

(1)

Only Y can cause the KMnO4 solution to change from purple to colourless

(1)

(Do NOT accept combustion.) (c)

General formula of alkene is CnH2n

1

12n + 2n = 42

(1)

n=3 Y is C3H6 (d)

1

(i) CH3CH=CH2  n (ii)

(e)

1

CH3 H C

C

H

H

Apply heat to Z to the shape of a cup in a mould and allow it to cool.

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Advantage: to reduce the consumption of non-renewable energy sources / fossil fuels

1

(also accept reduction of solid waste for landfill.) Disadvantage: Burning plastic wastes produces air pollutants / toxic gases or, the cost to the remove the pollutants produced by burning plastic wastes is high. 6.

1 (1)

(a)

(saturated) hydrocarbon / alkane

1

(b)

(i)

vapour

1

(ii)

oxygen (air) and high temperature

1,1

(DO NOT accept oxidant.) (c)

The high temperature of molten wax causes water to evaporation rapidly.

1

The steam produced causes the molten candle wax to splash out. The hot wax may cause burning of skin.

1

Or, The steam produced causes the wax to form tiny drops of wax which can easily catch fire / burn violently. (1) 7. Chemical knowledge (6 marks) Notes: The chemical knowledge covers three different areas (see below). Award a maximum of 2 for each area.

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds

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(Award 2 marks for characteristic related to structure / formula; 2 marks for physical property; 2 marks for chemical property.) Members of a homologous series can be represented by the same general formula General formula of alkenes: CnH2n

1 1

Or, Successive members of a homologou series differ in their structure by one CH2 unit

(1)

Formulae: ethane (C2H4), propene (C3H6) etc.

(1)

Or, Members of a homologou series have the same functional group

(1)

Functional group of alkenes: C=C (1) Or, Alkenes possess the C=C functionality (1) Structures of alkenes: ethane (CH2=CH2); propene (CH3CH=CH2) (1) Their physical properties change gradually from one member to the next

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(with no. of carbon atoms) The melting point / boiling point of alkene increases with increase in relative molecular mass/ The volatility / flammabitity of alkenes decreases with increase in relative molecular mass

1 (1)

Members of a homologous series have similar chemical properties

1

One example of the reactions of alkenes which is characteristic of unsaturated hydrocarbons

1

(accept a description of the reaction or a chemical equation.) (do NOT accept combustion alone) e.g. CH2=CH2 + Cl2  CH2Cl-CH2Cl KMnO4/ H+ CH2=CH2 + (O) + H2O --------------> CH2-CH2 |

|

OH OH (Accept other reactions.) Effective communication (3 marks) 8.

(a)

concentrated sulphuric acid/ conc. H2SO4/ H2SO4(l)

(b)

Diagram:

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Heating under reflux

(1 mark for the diagram; 1 mark for direction of water flow in the condenser) (0 mark for wrong set-up, closed systems)

9.

(c)

flammable / C

(d)

Any ONE of the following:

(a)

no. of moles of SO2 released = no. of moles of S

1 1+1

Chemistry HKCEE Past Paper Fossil Fuels and Carbon Compounds = (1000 x 0.015) / 32

10 1

= 15 / 32 volume of SO2 released = 15 / 32 x 24

1 (method)

= 11.25 dm3

1

3

(Accept 11 to 11.3 dm ) (b)

acid rain / high incidence of respiratory illnesses / corrosion of buildings / damage respiratory system / reduce field of crop

1

(c)

installation of scrubbers / installation of desulphurization system / use coal of lower sulphur content

1

(d)

(i)

high incidence of respiratory illnesses / causing cancer / darkening of building walls / reduce visibility / smog

1

(Do NOT accept photochemical smog) (ii) 10.

(a)

installation of electrostatic precipitator

sewage sludge / manure / dead plant / dead animal

1 1

(Accept other reasonable answers.) (b)

CH4 + 2O2  CO2 + 2H2O

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(c)

Save fossil fuels / as a renewable energy source / reduce solid wastes

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(d)

Any ONE of the following:

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Methane produced in biogas plants cannot meet the huge demand of domestic fuel. Investment in the construction of biogas plants may be great. Biogas plants release air pollutants. Difficult to collect large amount of organic wastes. (Accept other reasonable answers.)