Ce Chemistry 2007 Paper 1

2007-CE CHEM PAPER 1 HONG KONG EXAMINATIONS AND ASSESSMENT AUTHORITY

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HONG KONG CERTIFICATE OF EDUCATION EXAMINATION 2007

CHEMISTRY PAPER 1 Question-Answer Book

Candidate Number

8.30 – 10.15 am (1¾ hours) This paper must be answered in English.

1. Write your Candidate Number in the space provided on Page 1.

2. Stick barcode lables in the spaces provided on Pages 1, 3, 5 and 7

3. This paper consists of TWO sections,Section A and

Section A Question No. 1

Marks

Marks

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answers in the spaces provided in this QuestionAnswer Book. Do not write in the margins.

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Question-Answer Book. Atomic numbers and relative atomic masses of element can be obtained from the Periodic Table.

Examiner No.

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4. Attempt ALL questions in each section. Write your

6. A Periodic Table is printed on Page 17 of this

Marker No.

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request. Write your Candidate Number and stick a barcode lable on each sheet, and fasten them with string INSIDE this book.

Examiner's Use Only

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Section B. Section A carries 54 marks and Section B carries 36 marks.

5. Supplementary answer sheets will be supplied on

Marker's Use Only

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Section A Total Checker's Use Only Section B Question No. 10

Section A Total

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11 12 13 Section B Total Checker's Use Only Checker No.

©香港考試及評核局 版權所有 Hong Kong Examinations and Assessment Authority All Right Reserved 2007 2007-CE-CHEM I-1 1

Section B Total

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SECTION A

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Answer ALL questions. Write your answer in the space provided. 1.

A is a compound formed from oxygen and magnesium, while B is a compound formed from oxygen and fluorine. (a)

Draw the electronic diagram of A, showing electrons in the outermost shells only. (1 mark)

(b)

Draw the electronic diagram of B, showing electrons in the outermost shells only.

(c)

Compare the melting points of A and B. Explain your answer. (2 marks)

2.

A student performed an experiment to crack paraffin oil and collect the gaseous products by using a boiling tube.

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(1 mark)

(a)

Total Draw a labelled diagram to show how this experiment can be performed in thePage laboratory. (3 marks)

(b) (i)

The student added a few drops of bromine water into the boiling tube containing the gaseous products. The brown colcur of bromine water disappeared immediately. Why?

(ii)

3.

The student then dropped more bromine water into the boiling tube until the brown colour of the bromine water persisted. After about 10 minutes, the brown colour disappeared. Why? (4 marks)

The diagram below shows the set-up used in performing a microscale experiment. A drop of hydrochloric acid was added to the drop of chlorine bleach in a petri dish and the dish was immediately covered with its lid. Chlorine gas formed by the reaction between chlorine bleach and hydrochloric acid eventually filled up the whole set-up.

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lid D

C

petri dish

a drop of acidified potassium permanganate solution

a drop of chlorine bleach and hydrochloric acid

(a)

Write a chemical equation for the reaction between chlorine bleach and hydrochloric acid. (1 mark)

(b)

State the expected observation at position C and position D. In each case, write a relevant chemical equation if a reaction occurred. (i)

Position C

(ii)

Position D (3

marks)

(c)

Suggest one advantage of replacing test tube experimnets with microscale experiments. (1 mark)

multimeter 4.

A student learnt from a book that an ancient chemical cell could be made by immersing an aron rod in a liquid placed inside a copper can. The liquid used was vineagr but not wine. The diagram below shows the set-up designed by him in silulating the cell. iron rod

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vineagr copper can

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A drop of potassium iodide solution

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(a)

Explain, in terms of structure and property of particles, why the liquid inside the ancient chemical cell was vinegar but not wine. (2 marks)

(b)

The student found that the iron rod dissolved gradually, and colourless gas bubbles were given out on the inner of the copper can.

(c)

5.

(i)

Write a half equation, involving iron, for the reaction that at the iron rod.

(ii)

Write a half equation for the reaction that occurred on the inner wall of the copper can. (2 marks)

The student found that colourless gas bubbles were also given out at the surface of the iron rod that immersed in vinegar. Explain the observation. (1 mark)

A solid sample contains zinc and copper only. The composition of the solid sample was analysed experimentally as outlined below:

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6.

(a)

Write a chemical equation for the reaction involved.

(1 mark)

(b)

How can one know that the reaction has been completed?

(1 mark)

(c)

Explain why it is necessary to wash the residue obtained.

(1 mark)

(d)

Explain why it is NOT apporpriate to dry the residue with a Bunsen flame after washing. (1 mark)

(e)

Assuming negligible experimental errors, calculate the percentage of zinc by mass in the solid sample. (2 marks)

Read the paragraph below and answer the questions that follow. Magnesium is a useful metal. Scientists adopt different methods to extract magnesium from magnesium oxide. In 1828, a scientist obtained magnesium in two

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2.00 g of the solid sample was added to excess dilute hydrochloric acid in a beaker. Upon completion of Total water, reaction, the mixture inside the beaker was filtered. The residue obtained was first washedPage distilled and then dried. The mass of the dried residue was 1.75 g.

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(a)

Write a chemical equation for the reaction that occurred in the first step of the method used by the scienists in 1828. (1 mark)

(b)

Name the type of reaction between potassium and magnesium chloride. Why can potassium react with magnesium chloride to give magnesium? (2 marks)

(c) (i)

What would be the chemical process that can obtain magnesium from magnesium chlorine, without using potassium or other chemicals, in 1951?

(ii)

(d)

7.

What property does magnesium chloride posses so as to make the chemical process possible? (2 marks)

Suggest one use of magnesium in dairy life.

(1 mark)

This question involves how to distinguish four unlabelled test tubes, each containing one of the following colourless liquids:

methanol, concentrated sodium hydroxide solution, distilled water, hexane (a)

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By heating a small amount of each of the colourless liquids to dryness, ONE of the liquids can

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steps. In the first step, magnesium oxide reacts with chlorine and carbon to form Page Total magnesium chlorine. In the second step, the magnesium chlorine formed reacts with potassium to give magnesium. In 1951, some scienists adopted another chemical process to obtain magnesium from magnesium chlorine. Potassium is not used in this process, and there is even no need to use any other chemicals.

be distinguished. Suggest which liquid can be distinguished, and state the observation Page Total involved. (2 marks)

8.

(a)

By applying a flame directly to a small amount of each of the colourless liquids, TWO of the liquids would catch fire. (i)

Suggest which two liquids would catch fire.

(ii)

For the two liquids that would catch fire, the observations involved during combustion are different. Suggest the difference in these observations, and explain your answer.

(iii)

Without using other chemicals apart from the above colourless liquids, suggest another method to distinguish the two liquids that would catch fire. State the expected observation. (Smelling is not accepted.) (4 marks)

Teflon is a plastic that can be used to make artifical hip joints. Teflon is an addition polymer of linear structure consisting of carbon and fluorine only. The ratio of the number of carbon atoms to the number of fluorine atoms in the polymer is 1 : 2. (i)

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Draw a portion of the teflon structure with 10 carbon atoms.

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(b)

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(ii)

Write the repeating unit of teflon, and suggest a possible monomer of teflon. Repeating Unit: Monomer:

Nylon is a polymer that can used to make carpets. A portion of the nylon structure is shown below: H H H H ∣ ∣ ∣ ∣ ––C––(CH2)4––C––N––(CH2)6––N––C––(CH2)4––C––N––(CH2)6––N––C––(CH2)4––C–– ∥ ∥ ∥ ∥ ∥ ∥ O O O O O O

(i)

With reference to the given structure, explain whether nylon is a thermoplastic or a thermosetting plastic.

(ii)

Suggest one reason why recycling of used carpets to recover nylon is difficult.

(iii) State one disadvantage of disposing of nylon carpets by incineration (3 marks)

For question 9, candidates are required to give answers in paragraph form. For this question, 6 marks will be awarded for chemical knowledge and 3 marks for effective communication. 9.

A certain brand of rust remover contains an acid of high concentration. The rust remover can be used for removing tough rust stains; while the rust remover, after dillution, can be used for removing comparatively light rust stains.

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(b)

(3 marks)

Write some instructions, with reasons, on how the rust remover can be used safely at home. Two Page Total semtences have been given below as an introduction. (9 marks)

The rust remover should be kept out of reach from children as it contains an acid of high

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concentration. The rust remover should not be swallowed because it is harmful.

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B

SECTION B

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Answer ALL questions. Write your answers in the spaces provided. 10.

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In an experiment to deternine the concentration of phosphoric acid (H 3PO4), 10.0 cm of the acid was first diluted to 250.0 cm3 with distilled water. 25.0 cm3 of the diluted solution was then transferred to a conical flask and titrated with a 0.025 M sodium hydroxide solution using phenolphthalein as indicator. 17.60 cm3 of sodium hydroxide solution was needed to reach the end point. (a)

Describe briefly how 10.0 cm3 of phosphoric acid can be diluted to 250.0 cm3 with distilled water in the laboratory. (2 marks)

(b)

Phosphoric acid reacts with sodium hydroxide in the titration according to the following equation:

H3PO4 + 2NaOH

Na2HPO4 + 2H2O

Calculate the molarity of the original phosphoric acid before dilution.

(c)

‘At the beginning of titration, the solution in the conical flask turned pink upon the addition of sodium hydroxide solution but became colourless immediately upon swirling. However, near the end point, the solution took longer time to become colourless upon swairling.’ Explain why the time needed for the solution to become colourless is different at the two stages mentioned above. (2 marks)

(d)

In the titration, the 0.025 M sodium hydroxide solution was used as a standard solution. (i)

What does the term ‘standard solution’ mean?

(ii)

Comment whether it is appropriate to prepare a standard solution of sodium hydroxide by the following procedure: ‘Weigh a sample of solid sodium hydroxide, dissolve it in some distilled water and make up to a known volume of solution.’ (2 marks)

11.

In a chemical plant, extraction of copper from ores involves roasting copper(I) sulphide with air inside a high temperature furnace. Copper(I) sulphide reacts with oxygen in air according to the following equation: Cu2S + O2 2Cu + SO2

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(3 marks)

Please stick the barcode lable here The copper so extracted contains impurities including metals such as silver, iron, zincPage and Total gold. The impure copper is then purified by electrolysis as illustrated in the diagram below:

pure copper anode

impure copper anode

copper(II) sulphate solution

12.

(a)

With reference to the reaction between copper(I) sulphide and oxygen, identify the species undergoing oxidation and the species undergoing reduction. Explain your answers in terms of changes in oxidation numbers. (2 marks)

(b)

Explain briefly how impure copper can be purified by electrolysis as illustrated in the diagram above. (2 marks)

(c)

Insoluble impurities deposit under impure copper anode as ‘anode sludge’. According to the information given, suggest what substances the anode sludge would contain. Explain your answer. (2 marks)

(d)

‘The concentration of copper(II) ions in copper(II) sulphate solution remains UNCHANGED in the above electrolysis.’ Is this statement correct? Explain your answer. (2 marks)

(e)

State TWO advantages of building a factory in which contact process is carried out near the chemical plant mentioned adove. (2 marks)

Organic compound Z contains carbon, hydrogen and oxygen only. Analysis of Z gives the following results: (I)

1.0 g of Z contains 0.401 g of carbon, 0.068 g of hydrogen and 0.531 g of oxygen.

(II)

1.0 g of Z, upon complete vapourisation, occupies 400 cm3 at room temperature and pressure.

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andoe sludge

(III) There are no observable changes when potassium carbonate solution is added to Z.

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(IV) Brown colour of bromine remains unchanged when several drops of bromine in organic solvent are added to Z. (Molar volume of gas at room temperature and pressure = 24 dm3) (a)

Calculate the empirical formula of Z. (2 marks)

(b)

Deduce the molecular formula of Z.

(c)

(i)

Suggest a possible structure of Z. Explain your answer.

(ii)

Give the systematic name for the compound represented by the structure you suggested in (i). (4 marks)

For question 13, candidates are required to give answers in paragraph form. For this question, 6 marks will be awarded for chemical knowledge and 3 marks for effective communication. 13.

Discuss the similarities and differences between soapy detergents and soapless detergents with reference to their raw materials, structure and properties. (9 marks)

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(2 marks)

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END OF PAPER

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