1996

POK OI HOSPITAL TANG PUI KING MEMORIAL COLLEGE

FIRST TERM EXAMINATION ( 1997-1998 )

S4 CHEMISTRY

Class : ________________ Date : __________________

Name : ________________ Time allowed: 90 minutes

Class Number : ________________ ( P.1 - P.7 /53 )

Instructions to students:

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

2.Answer ALL questions.

3. Write your answers on the foolscap papers provided.

4. The total score is 100 marks.

________________________________________________________________________

Section A : Multiple Choice Questions ( 40 % )

Neon exists as a gas at room temperature and pressure because

A. neon molecules are monoatomic.

B. Neon is chemically inert.

C. The outermost shell of a neon atom has an octet structure

D. There are weak van der Waals’ forces between neon atoms.

The atomic number and mass number of element X are 8 and 17 respectively. What are the numbers of protons and neutrons in an atom of X

Number of protons Number of neutrons

A. 8 9

B. 8 17

C. 9 8

D. 9 17

When a sodium atom becomes a sodium ion,

A. its relative atomic mass changes by one unit,

B. it loses one electron.

C. It gains one electron.

D. Its atomic number changes by unit.

Element X consists of two isotopes. The table below lists the relative abundance of these two isotopes.

Isotope Relative abundance

55%

45%

The relative atomic mass of X (correct to 1 decimal place ) is

A. 79.0

B. 79.5

C. 79.9

D. 80.0

Strontium is a Group II element below calcium in the Periodic Table. Which of the following statements about strontium in likely to be FALSE?

A. Strontium atom has 2 outermost shell electrons.

B. Strontium is more reactive with calcium

C. Strontium shows no reaction with water.

D. Strontium forms salts with non-metals.

To which group does the element belong?

A. Group I B. Group II C. Group IV D. Group V

Consider the following set-up.

The light bulb in the set-up does NOT light up because

A. no solid can conduct electricity.

B. nichrome cannot conduct electricity.

C. solid lead(II) bromide contains molecules only.

D. solid lead(II) bromide contains no mobile ions.

Element X and Y form a compound having the following electron diagram:

(Only the outermost shell electrons are shown.)

Which of the following combinations is correct?

X Y

A. Na Cl

B. Al F

C. N Cl

D. Si N

Consider the following set-up. Electricity is passed through a gel containing copper(II) chromate and dilute hydrochloric acid. What are the observable colour changes in the set-up?

Positive electrode Negative electrode

A. Blue Yellow

B. Orange Green

C. Green Orange

D. Purple Blue

X and Y are elements. The melting points of their chlorides are given below:

	Melting point(^oC)
Chloride of X	974
Chloride of Y	-86

Which of the following statements is CORRECT?

A. Both X and Y are non-metals.

B. The chloride of X a gas at room temperature.

C. The chloride of Y conducts electricity in the solid state.

D. The chloride of X is an ionic compound.

Metallic bond refers to the attractive forces between

A. positive ions and negative ions.

B. positive ions and electrons.

C. protons and neutrons.

D. neutrons and electrons.

Which of the following statements about recycling of metals are true?

(1) Fuel can be saved by recycling.

(2) Environmental problems can be reduced by recycling.

(3) Aluminium is the only metal that is recycled at present.

A. (1) and (2) only. B. (1) and (3) only.

C. (2) and (3) only. D. (1), (2) and (3).

Which of the following pairs of substances will react when mixed?

A. Calcium and steam.

B. Aluminium and cold water.

C. Platinum and dilute hydrochloric acid

D. Zinc and magnesium nitrate solution.

Aluminium is used to make window frames because

(1) it is strong.

(2) It is the most abundant metallic element in the Earth’s crust.

(3) It can resist corrosion.

A. (1) and (2) only. B. (1) and (3) only.

C. (2) and (3) only. D. (1), (2) and (3).

In which of the following process will lead (Pb) be produced?

(1) Heating lead(II) oxide strongly.

(2) Electrolysis of molten lead(II) bromide.

(3) Adding magnesium to lead(II) nitrate solution

A. (1) only. B. (2) only.

C. (1) and (3) only. D. (2) and (3) only.

Which of the following ionic equations represent reactions that are likely to take place?

(1) 2Ag (s) + Cu²⁺ (aq) ® 2Ag⁺ (aq) + Cu (s)

(2) Zn (s) + Fe²⁺ (aq) ® Zn²⁺ (aq) + Fe (s)

(3) Mg (s) + 2Ag⁺ (aq)® Mg²⁺ (aq) + 2 Ag (s)

A. (1) and (2) only. B. (1) and (3) only.

C. (2) and (3) only. D. (1), (2) and (3).

Which of the following statements about the rusting of iron is NOT true?

A. Rusting is speeded up by a high temperature.

B. Rusting is speeded up by the presence of dilute acid.

C. Rusting is speeded up if iron is connected to another metal which is more reactive than iron.

D. Rusting is speeded up by the presence of sodium chloride solution.

Which of the following methods CANNOT prevent iron from rusting?

A. Coating iron with chromium.

B. Coating iron with plastics.

C. Joining a copper block to iron.

D. Using an alloy of iron containing chromium and nickel.

Tin-plating, rather than zinc plating, is used to prevent rusting of food can because

A. zinc corrodes more readily than tin.

B. Zinc is more expensive than tin.

C. Zinc is denser than tin.

D. Zinc ions are poisonous while tin ions are non-poisonous.

Which of the following elements is/are present in bronze?

(1) Copper (2) Nickel (3) Tin

A. (1) only. B. (2) only.

C. (1) and (3) only. D. (2) and (3) only.

Section B Questions (60%)

The following table gives some information about A, B, C and D which represent particles of some elements. These particles are either atoms or ions.

Element	Mass number	Atomic number	Number of proton	Number of electron	Number of neutron
A		12		12	12
B			12	10	12
C	35	17		17
D			17	17	20

(a) In which group of the Periodic Table should A be placed? Explain your answer.

(b) What is the relationship between A and B?

(i) Draw the electron diagram of a molecule of C, showing electrons in the outermost shells only.

(ii) Do molecules of C and of D have the same chemical properties? Explain your answer.

(iii) What type of bonding exists in the molecule of C.

(d) Element A and C forma compound X.

(i) Draw the electron diagram of the compound X, showing electrons in the outermost shells only.

(ii) What type of bonding exists in the compound X.

(10 marks)

The diagram below show the structures of three solid substances A, B and C.

(a) Name three substances which have the same structures as A, B and C respectively.

(b) There is a great difference in melting point between

(i) A and B

(ii) A and C

In each case, explain the difference in melting point in terms of the forces between particles and state which of the two solids is expected to have the higher melting point.

(c) Substance B cannot conduct electricity in solid state but it can conduct electricity in molten state. Explain briefly

(d) Do you expect substance C to dissolve in water? Explain your answer.

(10 marks)

The table below gives some information about five metals.

Metal	Abundance in the Earth’s crust(%)	Price per kg ($)	Conductivity of electricity (1=worst conductor, 4=best conductor)	Relative resistance of corrosion (1=least resistant, 4=most resistant)	Relative strength of metal (1=lowest, 3=highest)
Al	8.1	170	3	3	1
Cu	0.0055	140	4	3	3
Au	0.0000004	1100000	1	4	2
Fe	5.0	20	2	1	3
Zn	0.007	160	2	2	2

(a) Why was gold discovered by man a long time ago although it has a very low abundance in the Earth’s crust?

(b) Which metal in the above table is usually used in making electrical wires? Explain briefly.

(d) Aluminium does not corrode easily. Why?

(e) Suggest how the strength of aluminium can be improved to make it more suitable for making aircraft.

(f) Based on the information given in the table, suggest ONE factor that affects the price of a metal.

(g) Suggest ONE other factor (not indicated in the table) that can also affect the price of a metal.

(10marks)

The properties of four metals, A to D are given in the following table.

	A	B	C	D
Heating in air	Turns black	A white powder produced (the powder is yellow when hot)	Give a brick-red flame	No reaction
Reaction with cold water	No reaction	No reaction	Gas bubbles given off slowly	No reaction
Reaction with dilute hydrochloric acid	No reaction	Gas bubbles given of readily	Gas bubbles given off violently	No reaction

Based on the information given above, answer the following questions.

(a) Arrange the four metals in descending order of reactivity.

(b) (i) Suggest what metal A might be.

(ii) Will there be any reaction when the oxide of A with a chemical formula of AO is heated with

charcoal? Write an equation for the change, if any.

(ii) Write an ionic equation for the reaction between metal B and dilute hydrochloric acid.

(d) (i) Suggest what metal C might be.

(ii) Write a chemical equation for the reaction between metal C and water.

(e) Metal D forms an oxide with a chemical formula of D₂O.

(i) Suggest what metal D might be.

(ii) Would there be any reaction between metal B and a solution of the nitrate of D? Write an

ionic equation for the change, if any. (10 marks)

(a) A small crystal of potassium permanganate was placed in the middle of a strip of filter paper. The paper had been moistened with sodium sulphate solution. After the circuit was closed, purple patch slowly moved as shown in the diagram.

(i) Why was the filter paper moistened with sodium sulphate solution?

(ii)Which ion was responsible for the purple patch?

(iii)Which electrode (P or Q) was positive pole?

(iv) Towards which electrode (P or Q) were potassium ions migrating? Why?

(v) If the above experiment had proceeded for some time and the positive and

negation poles were then reversed, state what would happen and explain

briefly.

(7 marks)

(b) A student treated three pieces of iron in different ways and placed them in dishes containing some

corrosion indicator. The pieces of iron were left for a week. The student found blue patches

developed in disk 1 as shown below. This indicated that rusting occurred in disk 1.

Explain why rusting occurred in dish 1 but not the other dishes.

(5 marks)

Describe an experiment to show that both air and water are necessary conditions for rusting to occur.

(You are required to give paragraph-length answer to the question. 3 of the marks will be awarded for the effective communication of knowledge in Chemistry.)

(8marks)

END OF PAPER