Past Paper_microscopic World

Chemistry HKCEE Past Paper The Microscopic World P.1/9

Part 3: The Microscopic World 1. The boxes below show some information about two atoms, hydrogen (H) and deuterium : (a)

Suggest a term to indicate the relationship between a hydrogen atom and a deuterium atom.

(b)

State the number of neutrons in a deuterium atom.

(c) Deuterium reacts with oxygen in the same way as hydrogen. 2 D2 (g) + O2 (g) ------> 2 D2O (l)

(exothermic)

The product of the reaction is known as ‘heavy water’. (i)

Explain why deuterium reacts with oxygen in the same way as hydrogen.

(ii)

Draw the electronic structure of ‘heavy water’, showing electrons in the outermost shells ONLY.

(iii) What is the formula mass of ‘heavy water’? (iv) 100 cm3 of deuterium and 100 cm3 of oxygen, both measured at room temperature and pressure, are allowed to react. Calculate the mass of ‘heavy water’ produced. (Relative atomic mass: O = 16.0; molar volume of gas at room temperature and pressure = 24.0 dm3) [8 marks] [1996-CE-7a] 2.

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

Atomic number 16 18 19 20

Relative atomic mass 32.1 39.9 39.1 40.1

Chemistry HKCEE Past Paper The Microscopic World P.2/9

(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 solution with pH less than 7. (8 marks) [2000-CE-2] 3.

Magnesium occurs naturally in three isotopic forms. The relative abundance of each isotope is shown in the table below: Isotope

24

Relative abundance (%)

Mg 78.6

25

Mg 10.1

26

Mg 11.3

(a) State the meaning of the term ‘isotopes of an element’. (b) Calculate the relative atomic mass of magnesium. (c) Is it possible to separate the isotopes of magnesium by chemical means? Explain your answer.

(4 marks) [2002-CE-6b]

4.

Both carbon and silicon are Group IV elements in the Periodic Table. (a) Draw the electronic diagram of a carbon dioxide molecule, showing electrons in the outermost shells only. (b) Explain why carbon dioxide can be used in fire fighting. (c) Explain why carbon dioxide is a gas, whereas silicon dioxide is a solid at room temperature and pressure. (d) Silicon can be obtained by heating silicon dioxide with carbon strongly. (i)

Write a chemical equation for the reaction involved.

(ii) Suggest ONE use of silicon.

(8 marks)

Chemistry HKCEE Past Paper The Microscopic World P.3/9

[2002-CE-8b]

5.

Consider the substances listed below: carbon dioxide nitrogen

hydrogen chloride

silicon dioxide

neon sodium chloride

(a) Diagrams (i), (ii) and (iii) below show the arrangements of particles, which can be atoms, ions or molecules, in some substances. For each diagram, choose ONE substance from the above list, which has the arrangement of particles as shown under room temperature and pressure.

(b) From the above list, identify ONE substance which gives an acidic solution when dissolved

Chemistry HKCEE Past Paper The Microscopic World P.4/9

in water. Write the chemical equation for the reaction involved.

(5 marks) [2003-CE-1]

6.

(a) The atomic numbers of sulphur and chlorine are 16 and 17 respectively. Draw the electronic diagrams of the following atoms: (i)

sulphur atom

(ii) chlorine atom (c) Chlorine reacts with sulphur to form a compound with relative molecular mass of 135.2. The compound contains 52.5 % of chlorine by mass. (i)

Deduce the molecular formula of the compound.

(ii) Draw the electronic diagram of the compound, showing electrons in the outermost shells only. (Relative atomic masses: S = 32.1, Cl = 35.5)

(6 marks) [2003-CE-3]

7. Na2O, MgO, SiO2 and SO2 are oxides of Period 3 elements in the Periodic Table. Discuss how the melting points of these oxides are related to their bonding and structure.

(9 marks) [2004-CE-5]

8.

A portion of the Periodic Table is shown below:

Period

2 3 4

I Li Na K

II Be Mg Ca

III B Al

Group IV C Si

(a) Identify ONE semi-metal in the above table.

V N P

VI O S

VII F Cl Br

0 Ne Ar

Chemistry HKCEE Past Paper The Microscopic World P.5/9

(b) Suggest why Group 0 elements seldom form compounds. (c) Using aluminium as an example, describe the bonding in metals. Hence, explain why metals are ductile. (d) Which metal and non-metal in the above table would react most vigorously with each other? (e) (i)

The atomic number of bromine is 35. The electronic arrangement of a bromine atom

can be represented as 2, 8, x, y. What are the values of x and y? (ii) At 5°C, the reaction of bromine with sodium hydroxide solution is similar to that of chlorine with sodium hydroxide solution. Write a chemical equation for the reaction of bromine with sodium hydroxide solution at this temperature.

(8 marks) [2004-CE-9a]

9.

An ion of element A has the following electronic arrangement:

Chemistry HKCEE Past Paper The Microscopic World P.6/9

(a) Name subatomic particles, X and Z. X: (b) (i)

Z: To which group of the Periodic Table does A belong?

(ii) State, with explanation, whether or not A can be found free in nature. (iii) Suggest one way to obtain A from natural sources.

(6 marks) [2005-CE-S-1]

10. John Dalton published the Atomic Theory in 1807. The theory includes the following points: • All matter is composed of atoms. • All the atoms of any one element are the same, and they are different from those of any other element. • Compounds are formed by the chemical combination of atoms in small, whole numbers. State which of these points is/are now considered inaccurate. Explain your answer. (4 marks) [2005-CE-S-3] 11. (a)

Calcium is an element in Group II of the Periodic Table. (i)

Calcium reacts with nitrogen to form calcium nitride, which is an ionic compound. Draw the electronic diagram of calcium nitride, showing electrons in the outermost shells only.

Chemistry HKCEE Past Paper The Microscopic World P.7/9

(ii)

Suggest a test to show that marble is a calcium-containing substance.

(3

marks) (b) Strontium (Sr) is another Group II element, It exists in several isotopic forms. (i)

What is the meaning of the term ‘isotope’?

(ii)

Strontiunm-90 (90Sr) is a radioactive isotope of strontium, and is one of the dangerous by-products of nuclear fission. Complete the table below by providing the relevant information for a 90Sr atom. Number of protons 90

Number of neutrons

Sr (2 marks)

(c) (i)

State the similarity between a calcium atom and a strontium atom in terms of electronic arrangement.

(ii) Children’s teeth require a large amount of calcium to grow. Scientists found that in areas where nuclear weapon tests were conducted above the ground, children’s teeth contained higher level of 90Sr. Suggest a reason for the findings of the scientists.

(2 marks) [2005-CE-1]