Chemistry 2000 Paper 1+Ans

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Hong Kong Examinations AuthorityAll Rights Reserved 2000

2000-CE-CHEM 1–1

HONG KONG EXAMINATIONS AUTHORITY

HONG KONG CERTIFICATE OF EDUCATION EXAMINATION 2000

CHEMISTRY PAPER 1

8.30 am – 10.00 am (1½ hours)This paper must be answered in English

1. There are TWO sections in this paper, Section A and Section B.

2. Answer ALL questions in Section A and any THREE questions inSection B.

2000-CECHEMPAPER 1

2000-CE-CHEM 1–2 – 1 –

Section A (Answer ALL questions.)

1. Six compounds are classified into two groups as shown in the table below :

Gas Solid

ammonia iron(III) oxide

carbon dioxide magnesium oxide

nitrogen dioxide potassium oxide

Reclassify these compounds into two groups according to

(a) one of their physical properties, and

(b) one of their chemical properties.(4 marks)

2. The table below lists some information about four elements, W, X, Y and Z :

Element Atomic number Relative atomic mass

W 16 32.1

X 18 39.9

Y 19 39.1

Z 20 40.1

(a) What is the meaning of the term ‘relative atomic mass’ ?

(b) State, with explanation, which of the above elements

(i) should be stored under paraffin oil.

(ii) is used to fill a light bulb.

(iii) forms an oxide which dissolves in water to give a solutionwith pH less than 7.

(8 marks)

保留版權 All Rights Reserved 2000

2000-CE-CHEM 1–3 – 2 – Go on to the next page

3. Consider the following materials :

aluminium, bronze, copper, lead, mild steel and titanium

For each of the tasks listed below, choose the ONE material which is best toaccomplish the task. Explain your choice in each case.

(a) making electrical wiring

(b) making overhead high voltage cables

(c) making ship propellers(6 marks)

For questions 4 and 5, candidates are required to giveparagraph-length answers. 3 of the marks for each ofthese two questions will be awarded for effectivecommunication of knowledge in Chemistry.

4. The mass of a sample of copper powder contaminated with copper(II) oxideis known. Describe how you would conduct an experiment to determine thepercentage by mass of copper powder in the sample. State the expectedobservation of the experiment.

(Hint : You may use an acid in the experiment.)(9 marks)

5. Describe the actions of food preservatives. Illustrate your answer withappropriate examples.

(9 marks)

End of Section A


2000-CE-CHEM 1–4 – 3 –

Section B (Answer any THREE questions.)

6. (a) The flow diagram below shows the stages involved in theextraction of zinc from zinc blende, ZnS.

roasting

Stage II

electrolysis

(i) The reaction in Stage I gives, apart from zinc oxide, agaseous product.

(1) Write the chemical equation for the reaction.

(2) Give ONE industrial use of the gaseous product.

(ii) Suggest how zinc oxide can be converted to zinc sulphatesolution in Stage II.

(iii) The zinc sulphate solution obtained contains ions of othermetals. During the electrolysis in Stage III, zinc metal isliberated at one of the electrodes.

(1) Suggest ONE way to remove ions of metalswhich are less reactive than zinc from the zincsulphate solution before electrolysis.

(2) Why is it not necessary to remove ions of metalswhich are more reactive than zinc from thesolution ?

(3) Write half equations for the reactions occurringat the anode and cathode during the electrolysis.

(iv) Give ONE use of zinc in daily life. (8 marks)

zinc blende zinc oxide

zinc sulphate solution

zinc Stage III

Stage I



6. (b) In Hong Kong, the supply of fresh water mainly comes from DongJiang (東江). After some preliminary treatment of the river waterin the water treatment plants, chlorine and calcium hydroxide aresuccessively added.

(i) Why are the following substances added to the riverwater ?

(1) chlorine

(2) calcium hydroxide

(ii) Chlorine can react with organic matter present in the riverwater to give trichloromethane which is harmful to humanbeings.

(1) Draw the structure of trichloromethane.

(2) Why is trichloromethane harmful to humanbeings ?

(3) Suggest ONE preventive measure to reduce theamount of organic matter in the river water.

(5 marks)

(c) Explain the following statements :

(i) In cold weather, a person trying to warm up a room with acoal fire soon gets dizzy.

(ii) Detergents can be used to clean up oil spillage in the sea.(5 marks)


2000-CE-CHEM 1–6 – 5 –

7. (a) The sour taste of citrus fruits is mainly due to citric acid which is aweak acid with the following structure :

(i) What is the meaning of the term ‘weak acid’ ?

(ii) Given that citric acid is a tribasic acid, write a chemicalequation for the complete neutralization of citric acid bysodium hydroxide solution.

(iii) In a titration experiment to determine the concentration ofcitric acid in orange juice, 25.0 cm3 of a sample of orangejuice required 10.0 cm3 of 0.30 M sodium hydroxidesolution to reach the end-point, at which the citric acid hadbeen completely neutralized.

(1) Given that the relative molecular mass of citricacid is 192, calculate the concentration of citricacid, in g dm–3, in the sample of orange juice.

(2) State ONE assumption in your calculation in (1).

(3) Given the following materials and apparatus,briefly describe how a 0.30 M sodium hydroxidesolution can be prepared.

1.20 M sodium hydroxide solutiondistilled water25.0 cm3 pipette50.0 cm3 volumetric flask, 100.0 cm3 volumetricflask and 250.0 cm3 volumetric flask (Only one ofthese flasks should be used.)

(10 marks)

CH2CO2H

C CO2H

CH2CO2H

HO



7. (b) Polystyrene can be prepared in the laboratory by heating a mixtureof styrene and kerosene under reflux.

(i) Draw a labelled diagram of the set-up used for heating themixture under reflux.

(ii) Suggest ONE safety precaution that should be taken whenheating the mixture. Explain your answer.

(iii) Styrene has the following structure :

C6H5CH=CH2

(1) What characteristic in the structure of styreneenables it to act as a monomer ?

(2) Write the chemical equation for thepolymerization.

(iv) Disposable lunch boxes are commonly made of expandedpolystyrene.

(1) Suggest ONE reason why polystyrene should beexpanded before it is used to make disposablelunch boxes.

(2) State whether you agree with the followingstatement. Explain your answer.

‘Landfilling is better than incineration for thedisposal of polystyrene wastes.’

(8 marks)


2000-CE-CHEM 1–8 – 7 –

8. (a) Crude oil is a mixture consisting mainly of alkanes. Fractionaldistillation of crude oil gives different petroleum fractions. Thetable below lists the length of carbon chain of the alkanes in someof the fractions.

Fraction Length of carbon chain

petrol/naphtha C5 – C10

kerosene C11 – C18

diesel C18 – C25

X C20 – C34

(i) Describe the principle underlying the fractional distillationof crude oil.

(ii) (1) Explain why the global demand for petrol isgreater than that for kerosene.

(2) Cracking kerosene can produce petrol. State theconditions required for the cracking process.

(iii) In Hong Kong, naphtha instead of coal is used tomanufacture town gas.

(1) State ONE advantage of using naphtha instead ofcoal to manufacture town gas.(You are NOT required to consider the price ofthe materials.)

(2) Explain why an additive with a foul smell isadded to town gas before it is delivered to theconsumers.

(iv) Give ONE use of fraction X in cars.(9 marks)



8. (b) In some countries, ‘gasohol’ (a mixture of petrol and ethanol) isused as fuel for cars.

(i) Explain why burning gasohol causes less air pollutionthan burning petrol.

(ii) Ethanol can be manufactured from a petroleum product.Name the manufacturing process and write the chemicalequation for the reaction involved.

(iii) Ethanol can also be manufactured by another process.Name this process.

(iv) Of the two processes you have mentioned in (ii) and (iii),which one is better for the manufacture of ethanol ingasohol ? Explain your answer.

(5 marks)

(c) State whether each of the following statements is true or false.Explain your answer in each case.

(i) The melting point of sodium chloride is much higher thanthat of methane because the ionic bonding in sodiumchloride is much stronger than the covalent bonding inmethane.

(ii) When concentrated sulphuric acid is diluted, water shouldbe added slowly to the acid.

(4 marks)


2000-CE-CHEM 1–10 – 9 –

9. (a) X, Y and Z are three different metals. The table below shows theresults of two experiments carried out using the metals or theiroxides.

Experiment X Y Z

Adding the metal to water

effervescence no observablechange

no observablechange

Heating the metal oxide

no observablechange

metal produced no observablechange

(i) Based on the above information, arrange the three metalsin order of increasing reactivity. Explain your answer.

(ii) An oxide of Y has the formula YO. When 1.08 g of thisoxide is heated strongly, it decomposes completely to give60.0 cm3 of oxygen, measured at room temperature andpressure. Calculate the relative atomic mass of Y.

(Relative atomic mass : O = 16.0; molar volume of gas at room temperature and pressure = 24.0 dm3)

(6 marks)



9. (b) Carbon dioxide constitutes about 0.03% of the atmosphere. Overmillions of years, the concentration of carbon dioxide in theatmosphere has remained almost constant because of a number ofprocesses.

(i) Suggest ONE process by which carbon dioxide is addedto the atmosphere.

(ii) Suggest ONE process by which carbon dioxide in theatmosphere is consumed.

(iii) Carbon dioxide is one of the greenhouse gases in theatmosphere.

(1) Explain why carbon dioxide can cause thegreenhouse effect.

(2) State the importance of the greenhouse gases inthe atmosphere to living things on earth.

(3) Increasing the concentration of the greenhousegases in the atmosphere leads to global warming.State ONE harmful effect of global warming.

(6 marks)

(This question is continued on the next page.)


9. (c) Nitrogen constitutes about 78% of the atmosphere. The flowdiagram below shows the conversion of atmospheric nitrogen toplant proteins.

(i) Draw the electronic diagram for a molecule of nitrogen,showing electrons in the outermost shells only.

(ii) Describe ONE process by which atmospheric nitrogen canbe converted to nitrates in soil.

(iii) When plants are eaten by animals, the plant proteins aretransformed into animal proteins. State ONE way bywhich the nitrogen in animal proteins can return to soil.

(4 marks)

(d) Fritz Haber, a German chemist, discovered the transformation ofatmospheric nitrogen to ammonia which can be used to producenitrogenous fertilizers and explosives. He also managed tosuccessfully use chlorine and mustard gas as chemical weapons. In1918, when he was awarded the Nobel Prize for chemistry, severalother Nobel Prize winners refused to accept their awards becauseof Haber’s involvement.

State whether or not you agree that Haber’s inventions contributedto the well-being of the world. Explain your answer.

(2 marks)

END OF PAPER

atmosphericnitrogen

nitratesin soil

plantproteins


2000

Chemistry 1

Section B

7. (a) (iii) (1) 7.68

9. (a) (ii) 200


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Chemistry 2000 Paper 1+Ans