chem+sem+2+str

8/18/2019 chem+sem+2+str

1/44

STPM Chemistry (Semester 2)

- 1 -

STPM CHEMISTRY

SEMESTER 2

PRE-EXAM PRACTICE

Section A: Structured Questions

Answer all questions.

1 (a) Chrome yellow has been used for a long time as a yellow pigment in oil

paintings.

SO42-(aq) + 4H+(aq) + 2e ⇌ 2H2O(l) + SO2(g) E o = +0.17 V

CrO42-(aq) + 8H+(aq) + 3e ⇌ 4H2O(l) + Cr 3+(aq) E o = +1.33 V

(i) By using the standard electrode potentials above, explain why the

yellow colour of the painting exposed to an atmosphere contains sulphur dioxide.

[2 marks]

(ii) Explain why this colour change takes a long time. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(iii) What colour change takes place? [1 mark ]

..........................................................................................................................................

(b) Li+(g) + Cl(g)

+121 Li+(g) +1

2Cl2(g) −364

Li+(g) + Cl-(g)

+520

Li(g) +1

2Cl2(g)

+159 Li(s) +1

2Cl2(g) H 6

−409

Li+Cl-(s)


2/44


- 2 -

(i) By using this cycle, calculate the lattice energy of lithium chloride.

[2 marks]

(ii) Hence, calculate the enthalpy change of solution of lithium chloride.

[2 marks]

(iii) Comment on the solubility of lithium chloride in water. [1 mark ]

..........................................................................................................................................

Trg 2010


3/44


- 3 -

2 (a) A Group 14 element forms a divalent ion that decolourises aqueous

acidified potassium manganite(VII).

(i) Name the element. [1 mark ]

..........................................................................................................................................

(ii) Write the equation for the reaction between the ion and acidified

manganate(VII) ion. [1 mark ]

..........................................................................................................................................

(b) Nitrogen exists in the atmosphere as N2 molecules. Nitrogen is inert.

(i) Explain the inertness of nitrogen. [1 mark ]

..........................................................................................................................................

(ii) Give two examples (other than the Haber process) of reactions

involving atmospheric nitrogen. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(c) In the laboratory, nitrogen is prepared by heating a mixture of ammonium

chloride and sodium nitrate(III).

(i) Write a balanced equation to represent the action of heat on the

mixture. [1 mark ]

..........................................................................................................................................

(ii) State the changes in oxidation states of nitrogen in the reaction.

[1 mark ]

..........................................................................................................................................

(iii) Nitrogen is also prepared by heating solid ammonium nitrate(III).

Explain why these method is considered dangerous. [1 mark ]

..........................................................................................................................................

(d ) Why is the presence of nitrogen dioxide in air polluting? [1 mark ]

..........................................................................................................................................

(e) Describe how oxides of nitrogen is eliminated from the exhaust gas by the

use of a catalytic converter. [1 mark ]

..........................................................................................................................................

Trg 2010


4/44


- 4 -

3 (a) When ammonium nitrate is heated, it liberates a colourless gas. The gas can

be used as anaesthetic.

(i) Name the gas. [1 mark ]

..........................................................................................................................................

(ii) Write the equation for the above reaction. [1 mark ]

..........................................................................................................................................

(iii) On the axes below, sketch the general trend in melting points for the

Period 3 elements. Explain the trend. [4 marks]

Melting point ( oC)

Na Mg Al Si P S Elements

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(b) Chromium is a d-block element. Chromium compounds are used widely in

the laboratory.

(i) Write the electronic configuration of Cr 3+ ion. [1 mark ]

..........................................................................................................................................

(ii) Briefly explain why the Cr 3+(aq) ion is coloured. [3 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

Trg 2009


5/44


- 5 -

4 (a) Refer to the data given below for questions 4(a)(i) – (ii).

H2O2 + 2H+ + 2e ⇌ 2H2O E ored = 1.776 V

H2O2 + 2e ⇌ 2OH- E ored = 0.88 V

MnO4- + 8H+ + 5e ⇌ Mn2+ + 4H2O E ored = 1.491 V

MnO4- + 2H2O + 3e ⇌ MnO2 + 4OH- E ored = 0.588 V

(i) Identify the strongest oxidising agent and the strongest reducing agent.

Write an equation for the reaction between the two of them. [3 marks]

Strongest oxidising agent : .........................................................................................

Strongest reducing agent : .........................................................................................

Equation : .........................................................................................

(ii) You wish to build an electrochemical cell that will produce the

highest possible electromotive force (e.m.f). Draw a fully labelled diagram to show the

cell that you will set up. Calculate the e.m.f of this cell. [4 marks]


6/44


- 6 -

(b) The table below shows the data about the carbonates of Group 2 elements.

Compound BeCO3 MgCO3 CaCO3 BaCO3

Decomposition

temperature (oC)

T 540 900 1360

(i) Predict T . [1 mark ]

..........................................................................................................................................

(ii) Explain the trend in decomposition by heat of Group 2 carbonates.

[2 marks]

..........................................................................................................................................

..........................................................................................................................................

SMJKST


7/44


- 7 -

5 (a) The tetrachlorides of Group 14 elements, examples CCl4, SiCl4, GeCl4,

SnCl4 and PbCl4 are liquids at room temperature. All the tetrachlorides, with exception

of CCl4, are hydrolysed in aqueous solution to form acidic solutions.

(i) State the molecular shape of all the Group 14 tetrachlorides.

[1 mark ]

..........................................................................................................................................

(ii) Write a balanced equation for the hydrolysis of SiCl4. [1 mark ]

..........................................................................................................................................

(iii) Explain why CCl4 does not undergo hydrolysis. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(b) Aqueous aluminium sulphate contains [Al(H2O)6]3+. Aqueous ammonia is

added to aqueous aluminium sulphate until in excess. The reaction that occurs in limited

aqueous ammonia is as follow:

[Al(H2O)6]3+(aq) + 3OH-(aq) Al(H2O)3(OH)3(s) + 3H2O(l)

(i) Describe one observation in the above reaction. [1 mark ]

..........................................................................................................................................

(ii) What chemical nature of the aluminium ion is shown in (b)(i)?

[1 mark ]

..........................................................................................................................................

(iii) What happens when excess aqueous ammonia is added to the solution?

Write an equation for the reaction involved. [3 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(iv) What chemical nature of the aluminium ion is shown in (b)(iii)?

[1 mark ]

..........................................................................................................................................

SMI


8/44


- 8 -

6 (a) (i) Write the electronic configuration of the scandium atom and

scandium(III) ion, Sc3+. [2 marks]

Sc : ..............................................................................................................................

Sc3+ : ..............................................................................................................................

(ii) State the colour of scandium(III) ion, Sc3+ and explain why the colour

is such. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(b) Chlorine is a greenish-yellow poisonous gas which is slightly soluble in

water.

(i) Write a balanced equation for the reaction that occurs when chlorine

gas is passed into water. [1 mark ]

..........................................................................................................................................

(ii) What would you observe when an excess of potassium iodide is added

to the solution obtained from the reaction and write the equation for the reaction.

[2 marks]

..........................................................................................................................................

..........................................................................................................................................

(c) A sodium halide reacts with cold concentrated sulphuric acid to give

colourless fumes. When heated, the mixture produces brown fumes.

(i) Name the halide ion in the sodium salt. [1 mark ]

..........................................................................................................................................

(ii) Write two balanced equations to explain the observations above.

[2 marks]

..........................................................................................................................................

..........................................................................................................................................

Pahang 2011


9/44


- 9 -

7 (a) The ionic radius of the Group 2 elements is given in the table below.

Ion Be2+ Mg2+ Ca2+ Sr 2+ Ba2+

Ionic radius (nm) 0.027 0.072 0.099 0.113 0.136

(i) Write the electronic configuration of Mg2+ ion and Sr 2+ ion.

[2 marks]

Mg 2+ ion : .....................................................................................................................

Sr 2+ ion : .....................................................................................................................

(ii) How would you expect the ionic radius of Al3+ ion to be compared to

that of Mg2+ ion? Explain your answer. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(iii) The hydrated Be2+ ion has the formula [Be(H2O)4]2+. State one

property shown by beryllium salts in water. [1 mark ]

..........................................................................................................................................

(b) The carbonates of the Group 2 elements decompose on heating.

(i) Write the chemical equation for the decomposition of magnesium

carbonate. [1 mark ]

..........................................................................................................................................

(ii) Explain why magnesium carbonate does not decompose

spontaneously. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(iii) The thermal stability of the carbonates increases with the proton

number of the element. Suggest an explanation for the effect of the size of the cation

on the thermal stabilities of the carbonates. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

Pahang 10


10/44


- 10 -

8 (a) Explain why the reactivity of Group 2 elements in the Periodic Table

increases when descending the group, from beryllium to barium. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(b) (i) Write a balanced equation for the reaction of hydrated beryllium ion,

[Be(H2O)4]2+, in water. [1 mark ]

..........................................................................................................................................

(ii) What is the property exhibited by the hydrated beryllium ion in the

reaction above? [1 mark ]

..........................................................................................................................................

(c) Explain briefly why beryllium ion forms covalent compounds compared to

other elements in the same group. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(d ) Nitric(V) acid is manufactured from ammonia in the Ostwald Process.

(i) Name the catalyst used in this reaction. [1 mark ]

..........................................................................................................................................

(ii) Write equation to show the formation of nitrogen monoxide in the

Ostwald Process. [1 mark ]

..........................................................................................................................................

(iii) Predict qualitatively the conditions of temperature and pressure that

will give a maximum yield of nitrogen monoxide at equilibrium. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

Pahang 2009


11/44


- 11 -

9 (a) The table below shows the structures of the elements in Period 3 in the

Periodic Table from Na to Cl.

Element Na Mg Al Si P S Cl

Structure Giant metallic structure Simple molecular

(i) What is the structure of silicon? [1 mark ]

..........................................................................................................................................

(ii) The elements in Period 3, from Na to S burn in oxygen when heated

to form their respective oxides. State the acid-base property of these oxides. [3 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(iii) Draw the Lewis diagram for SO2. [1 mark ]

(b) The nitrates of Group 2 elements decompose on heating.

(i) Write the equation for the decomposition of magnesium nitrate.

[1 mark ]

..........................................................................................................................................

(ii) What is observed when magnesium nitrate is heated strongly?

[1 mark ]

..........................................................................................................................................

(c) How does the solubilities of the Group 2 sulphates change when moving

down the group? Explain your answer. [3 marks]..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

NS 11


12/44


- 12 -

10 (a) Carbon dioxide and nitrogen dioxide are gaseous combustion products of

liquid hydrocyanic acid, HCN at 298 K and 1 atm. Water is also formed in the

combustion.

(i) Define the standard enthalpy change of combustion of hydrocyanic

acid. Write a thermochemical equation for this enthalpy change. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(ii) The standard enthalpy change of combustion of hydrocyanic acid is

− 1628 kJ mol-1. The standard enthalpy changes of formation of carbon dioxide,

nitrogen dioxide and water are −393 kJ mol-1, −89 kJ mol-1 and −286 kJ mol-1

respectively. Calculate the standard enthalpy change of formation of hydrocyanic acid.

[3 marks]

(iii) Name the shapes of carbon dioxide and nitrogen dioxide. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(b) An aqueous solution of 0.100 mol dm-3 sulphuric acid is electrolysed in an

electrolytic cell using graphite electrodes. Calculate the time of electrolysis required to

produce 140 cm3 of gas at the anode at s.t.p when the current used is 1.25 A.

[3 marks]

NS 2010


13/44


- 13 -

11 (a) Aqueous ammonia is added to aqueous aluminium sulphate slowly until in

excess.

(i) What will be observed when aqueous ammonia is added slowly?

[1 mark ]

..........................................................................................................................................

(ii) Write an equation for your observation above. [1 mark ]

..........................................................................................................................................

(iii) What will be observed at the end of the reaction after excess ammonia

is added? Write the formula of the aluminium species at the end of the reaction.

[2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(b) The table below shows two iron complexes.

Complex Colour Name

[Fe(CN)6]2- Yellowish-green

[Fe(SCN)(H2O)5]2+ Red

(i) Write the names of the iron complexes in the above table. [2 marks]

(ii) State two properties of iron that enable it to form complex ions.

[2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(iii) Why are transition metal complex ions coloured? [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

NS 2010


14/44


- 14 -

12 (a) Write the formula of the oxides of Period 3 elements of the Periodic Table

in the table below. Give only one formula for each element. [3 marks]

Element Na Mg Al Si S Cl

Formula

of oxide

(b) Write equations for the reactions of aluminium oxide with the following

reagents.

(i) Aqueous sodium hydroxide. [1 mark ]

..........................................................................................................................................

(ii) Aqueous hydrochloric acid. [1 mark ]

..........................................................................................................................................

(c) Strontium, Sr is an element in Group 2 of the Periodic Table.

(i) Write a balanced equation for the action of heat on strontium nitrate.

[1 mark ]

..........................................................................................................................................

(ii) Both magnesium nitrate and strontium nitrate will decompose on

heating. Which of the two will decomposes at a lower temperature? [1 mark ]

..........................................................................................................................................

(iii) Explain your answer in (c)(ii). [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(d ) Arrange the solubilities of Group 2 sulphates in descending order.

[1 mark ]

..........................................................................................................................................

NS 09


15/44


- 15 -

13 (a) The yellow gas, chlorine dioxide, ClO2, has been used for many years as

flour-improving agent in bread making. It can be made in the laboratory by the

following reaction.

2AgClO3(s) + Cl2(g) 2AgCl(s) + 2ClO2(g) + O2(g) H = 0 kJ

(i) Give the oxidation state of Cl in ClO2. [1 mark ]

..........................................................................................................................................

(ii) Chlorine dioxide disproportionates to form a mixture of chlorate(III)

and chlorate(V) ions in alkaline solution. Write a balanced equation to illustrate the

reaction that occurs. [1 mark ]

..........................................................................................................................................

(iii) Given that the standard enthalpies of formation of AgClO3 and AgCl

are −25 kJ mol-1 and −127 kJ mol-1 respectively. Calculate and comment on the value

of the standard enthalpy of formation of chlorine dioxide. [4 marks]

Comment : .........................................................................................................................

..........................................................................................................................................

(b) The standard electrode potentials of the following systems are given below.

System E o / V

ClO2(aq) + 4H+(aq) + 5e ⇌ Cl-(aq) + 2H2O(l) +1.50

S(s) + 2H+(aq) + 2e ⇌ H2S(aq) +0.14

By using the standard electrode potentials given above, predict whether

chlorine dioxide in an acidic solution reacts with aqueous hydrogen sulphide. Give your

reason. [4 marks]

Melaka 2009


16/44


- 16 -

14 Several standard electrode potentials are shown below.

Half-cell E o / V

Ag+ + e ⇌ Ag +0.80

1

2Cl2 + e ⇌ Cl-

+1.36

Cu2+ + 2e ⇌ Cu +0.34

Fe3+ + e ⇌ Fe2+ +0.77

1

2I2 + e ⇌ I- +0.54

(a) (i) Draw a labelled diagram to show how the cell potential of an

electrochemical cell consisting copper and silver half-cells can be measured. [2 marks]

(ii) On the diagram, show the direction of electron flow in the circuit.

[1 mark ]

(iii) Write the cell diagram for the above set-up. [1 mark ]

..........................................................................................................................................

(iv) Write the overall cell reaction. [1 mark ]

..........................................................................................................................................(v) Calculate the standard cell potential. [1 mark ]

(vi) Calculate the cell potential if the solution containing silver ions is

replaced with 0.10 mol dm-3 aqueous silver nitrate while other factors remain

unchanged. [2 marks]


17/44


- 17 -

(b) Chlorine will oxidises Fe2+ to Fe3+ but iodine does not. Explain why by

using the electrode potentials data. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

Kelantan 12


18/44


- 18 -

15 (a) (i) Explain the term complex ion. [2 marks]

….......................................................................................................................................

….......................................................................................................................................

….......................................................................................................................................

(ii) 1,2-ethenediamine is a chelating ligand. Explain the term chelating

ligand . [1 mark ]

….......................................................................................................................................

….......................................................................................................................................

(b) A series of experiments were carried out on an aqueous solution of

copper(II) sulphate. The table below shows the observations obtained.

Experiment Observation

Aqueous sodium hydroxide is added to

copper(II) sulphate solution.

A blue precipitate is formed.

Aqueous ammonia is added to copper(II)

sulphate solution until in excess.

The blue precipitate dissolves and

a dark blue solution is obtained.

(i) Write down the formulae of all the complex ions in the experiments.

[2 marks]

….......................................................................................................................................

(ii) Arrange the ligands in order of increasing strength with respect to

copper(II) ions. Explain your answer. [2 marks]

….......................................................................................................................................

….......................................................................................................................................

….......................................................................................................................................

(iii) Explain why transition element complex are often coloured, whereas

compounds of other elements are usually white. [3 marks]

….......................................................................................................................................

….......................................................................................................................................

….......................................................................................................................................

….......................................................................................................................................

Kelantan 12


19/44


- 19 -

16 An important use of silicon compounds is to make glass. The simplest form of

glass is soda glass which is produced by melting silica, SiO2, sodium carbonate and

calcium carbonate at about 1800 K.

(a) Name a substance which can be added to soda glass in order to

(i) increase its melting point. [1 mark ]

..........................................................................................................................................

(ii) give a coloured product. [1 mark ]

..........................................................................................................................................

(b) Give a difference in terms of bonding and structure between glass and ionic

crystal. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(c) Group 14 elements can react with chlorine to form tetrachlorides.

(i) In the following table, give the name of the process (if any) and the

equation for the reaction which occurs. [4 marks]

Action of water Equation of reaction

CCl4

SiCl4

PbCl4

(ii) Explain the differences of the reaction between the three

tetrachlorides above with water. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

Kelantan 2009


20/44


- 20 -

17 (a) The standard electrode potentials, at 298 K, of some half-cells are given

below.

Half-cells E o / V

Ge4+(aq) + 2e ⇌ Ge2+(aq) −1.60

Sn4+(aq) + 2e ⇌ Sn2+(aq) +0.15

Pb4+(aq) + 2e ⇌ Pb2+(aq) +1.80

(i) Arrange the Ge4+, Sn4+ and Pb4+ ions in order of decreasing stability

in aqueous solutions. [1 mark]

..........................................................................................................................................

(ii) Which ion is the strongest reducing agent? [1 mark]

..........................................................................................................................................

(iii) Which ion is more stable in aqueous solutions, Pb2+ or Pb4+? Explain

your answer. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(b) An important application of glass is to make optical fibres. A laser beam

can travel along an optical fibre which is as thin as human hair.

(i) State the main component of glass. [1 mark]

..........................................................................................................................................

(ii) State one use of optical fibre. [1 mark]

..........................................................................................................................................

(iii) In certain applications, optical fibres have many advantages over

copper wire. State two advantages of optical fibres over copper wire. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(iv) State the difference in the structure between glass and diamond.

[2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................


21/44


- 21 -

18 (a) Aluminium chloride, Al2Cl6 is formed when aluminium reacts with chlorine

gas.

(i) Write a balanced chemical equation for the above reaction. [1 mark ]

..........................................................................................................................................

(ii) State one important use of aluminium chloride. [1 mark ]

..........................................................................................................................................

(iii) If 2.00 g of aluminium was added in the reaction, 4.60 g of aluminium

chloride would be produced. Calculate the percentage yield of the product. [3 marks]

(b) Write the observation when sodium hydroxide solution is added to an

aqueous solution of aluminium sulphate until in excess. [1 mark ]

..........................................................................................................................................

(c) Explain why

(i) an aluminium pot should not be used to boil strongly alkaline soup.

[1 mark ]

..........................................................................................................................................

(ii) aluminium is not easily corroded as iron. [1 mark ]

..........................................................................................................................................

(d ) Write the chemical equations for the reaction of chlorine with

(i) cold aqueous sodium hydroxide. [1 mark ]

..........................................................................................................................................

(ii) hot aqueous sodium hydroxide. [1 mark ]

..........................................................................................................................................

Kedah 2009


22/44


- 22 -

19 (a) (i) Give the definition of standard electrode potential . [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

The standard reduction electrode potentials for several half-cell reactions at

298 K are given in the table below.

Half-cell reaction E o / V

S2O82- + 2e 2SO4

2- +2.01

[Fe(CN)6]3- + e [Fe(CN6)]

2- +0.36

Fe3+ + e Fe2+ +0.77

I2 + 2e 2I-

+0.54

When an aqueous solution of potassium peroxodisulphate, K 2S2O8 is added

to an aqueous solution of potassium iodide, KI, a reddish-brown solution is obtained.

(ii) Write a balanced ionic equation for the above reaction. [2 marks]

..........................................................................................................................................

(iii) Write a cell diagram for the above reaction. [1 mark ]

..........................................................................................................................................

(iv) Calculate the standard cell e.m.f, Eocell for the reaction in (b)(iii).

[1 mark ]

(c) Strips of copper are dropped into a conical flask containing 50% hot nitric

acid solution. A colourless and very reactive gas is given off. The gas then reacts with

oxygen in air to form a brown gas.

(i) Name the colourless gas. [1 mark ]

..........................................................................................................................................

(ii) Write the equation for the reaction between copper and nitric acid.

[1 mark ]

..........................................................................................................................................

(iii) Identify the brown gas. Write equation for its formation. [2 marks]

..........................................................................................................................................


23/44


- 23 -

20 (a) Define the following.

(i) First electron affinity. [1 mark ]

..........................................................................................................................................

..........................................................................................................................................

(ii) Second electron affinity. [1 mark ]

..........................................................................................................................................

..........................................................................................................................................

(b) Write equations to represent the first and second electron affinities for an

oxygen atom. [2 marks]

First electron affinity : .........................................................................................

Second electron affinity : .........................................................................................

(c) The first electron affinity for oxygen atom is −141 kJ mol-1 whereas the

second electron affinity is +798 kJ mol-1. Explain why the first electron affinity is

exothermic while the second electron affinity is endothermic. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(d ) The decomposition temperatures of nitrates of Group 2 elements is shown

below.

Nitrate Be(NO3)2 Mg(NO3)2 Ca(NO3)2 Sr(NO3)2 Ba(NO3)2

Temperature (K) 320 390 460 670 820

(i) Write a balanced equation for the decomposition of one of the nitrate.

[1 mark ]

..........................................................................................................................................

(ii) Give a brief account for the trend of temperature of decomposition of

Group 2 nitrates. [3 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

Johor 10


24/44


- 24 -

21 Consider the incomplete Born-Haber cycle and the table of data below.

..........................................

..........................................

..........................................

Ca2+(g) + 2Cl-(g)

..........................................

Ca(s) + Cl2(g)

CaCl2(s)

Standard enthalpy change Value / kJ mol -1

Enthalpy of atomisation of Cl +121

Enthalpy of atomisation of Ca +178

First ionization energy of Ca +590

Second ionization energy of Ca +1145

Electron affinity of Cl −364

Lattice energy of CaCl2 −2237

(a) Complete the Born-Haber cycle above. [3 marks]

(b) Using the cycle and the values given in the table, calculate the standard

enthalpy of formation of calcium chloride. [2 marks]


25/44


- 25 -

(c) The standard enthalpies of hydration of the Ca2+ and Cl- ions are −1650 kJ

mol-1 and −364 kJ mol-1 respectively. Use this information and data from the table to

calculate the enthalpy of solution of calcium chloride. [2 marks]

(d ) The standard enthalpy of solution of ammonium chloride, NH4Cl is +15 kJ

mol-1. A 2.0 g sample of ammonium chloride is dissolved in 50 g of water. Both

substances are initially at 20oC. Calculate the temperature change and the final

temperature of the solution. Assume that the specific heat capacity of the solution is 4.2

J K -1 g-1. [3 marks]


26/44


- 26 -

22 Aluminium is the first element of Group 13 in the Periodic Table.

(a) State the valence electronic configuration of aluminium. [1 mark ]

..........................................................................................................................................

(b) When aqueous sodium hydroxide is added to an aqueous solution of

aluminium chloride, a white precipitate, P , is formed. The precipitate dissolves in

excess sodium hydroxide, forming an ion, Q.

(i) Name the precipitate P . [1 mark ]

..........................................................................................................................................

(ii) Give the formula of ion Q. [1 mark ]

..........................................................................................................................................

(c) An aqueous solution of aluminium salt is acidic.

(i) Describe what you would observe when aqueous sodium carbonate is

added to aqueous aluminium chloride. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(ii) Write an ionic equation for the reaction above. [1 mark ]

..........................................................................................................................................

(d ) Aluminium chloride can be used as catalyst in Friedal Craft alkylation of

benzene.

(i) Write an equation for the reaction between aluminium chloride and

chloromethane, CH3Cl, to form an electrophile. [1 mark ]

..........................................................................................................................................

(ii) Use your understanding of acids and bases to explain the role of

aluminium chloride in the reaction above. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(iii) State one property which enables aluminium to be used in overhead

electric cables. [1 mark ]

..........................................................................................................................................

Johor 2009


27/44


- 27 -

23 (a) Nitrogen can be produced by warming a mixture of ammonium chloride

and sodium nitrite, NaNO2. Steam is also produced and a solid is left.

(i) Suggest an identity for the solid. Write a balanced equation for the

reaction. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

(ii) Write a balanced equation to show how ammonium chloride can be

used to prepare ammonia in the laboratory. [1 mark ]

..........................................................................................................................................

(iii) Explain why nitric acid is usually kept in dark bottles. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................

(b) Ammonia is very soluble in water. At room temperature, 100 cm3 of its

saturated solution contains 33.0 g of ammonia.

(i) Suggest why ammonia is so soluble in water. [1 mark ]

..........................................................................................................................................

..........................................................................................................................................

(ii) Calculate the concentration of a saturated solution of ammonia, in

mol dm-3. [2 marks]

(iii) Describe and explain what happens when a saturated solution of

ammonia is shaken with silver bromide. [2 marks]

..........................................................................................................................................

..........................................................................................................................................

..........................................................................................................................................


28/44


- 28 -

Section B (Essay Questions)

Answer all questions.

1 (a) With the help of a labelled diagram, explain how to determine the standard

electrode potential for copper. [5 marks]

(b) Write a balanced reaction for the reaction in the cell below.

Cu(s) | Cu2+(aq) || Fe3+(aq) , Fe2+(aq) | Pt(s)

and calculate the standard electrode potential, E o, of this cell. [2 marks]

(c) (i) Explain the term standard enthalpy change of combustion.

(ii) Write a balanced equation for the complete combustion of ethanol.

(iii) When 1.00 g of ethanol was burned under a container of water, 100 g

of water was heated from 15oC to 65oC. The process was known to be only 70%

efficient. Calculate the enthalpy change of combustion per mole of ethanol.

(iv) Using the value you have calculated in (iii) and the following data,

calculate the enthalpy change of formation of ethanol from its elements.

Enthalpy change of combustion of C = −393.5 kJ mol-1

Enthalpy change of combustion of H = −285.8 kJ mol-1

[9 marks]

Johor 08

2 (a) Describe and explain what happens in each of the following experiments.

(i) Bromine is added to cold, aqueous sodium hydroxide.

(ii) Concentrated sulphuric acid is added to solid potassium bromide and

the mixture is heated.

(iii) Aqueous silver nitrate is added to aqueous sodium chloride and

aqueous ammonia is then added to the resulting mixture.

Write balanced equations for the reactions that occur. State the observations

and the type of reaction. [9 marks]

(b) Ammonia and chlorine react in the gas phase to give gaseous nitrogen and

solid ammonium chloride. Write a balanced equation for this reaction and explain how

ammonia is behaving both as reducing agent and as a base. [3 marks]

(c) Suggest an explanation for the decreasing solubilities of the Group 2

sulphates as the proton number of cations increases. [3 marks]

Johor 08


29/44


- 29 -

3 (a) (i) State the trend in the reducing ability of the halide ions from fluoride

to iodide. [1 mark ]

(ii) State what you would observe when chlorine water reacts with

solution of potassium iodide. Write an equation for the reaction. State the role of

chlorine in the reaction. [3 marks]

(iii) Name a reagent which can be used to distinguish between separate

solutions of potassium bromide and potassium iodide. State what would be observed

when this reagent is added to each of the solutions. Write an equation for one of the

reactions. Identify a reagent which could be added to the mixtures from the first test to

confirm the identities of the halide ions. State what would be observed in each case.

[6 marks]

(b) Carbon tetrachloride and silicon tetrachloride behave in different ways

when added into water. State how each chloride behaves and explain the difference.

[5 marks]

Johor 09

4 (a) An aqueous solution of magnesium nitrate and barium nitrate can be

differentiated by the addition of dilute sulphuric acid. State what you would observe

when the above reaction is carried out. [3 marks]

(b) Compare and explain the solubility in water, for the solid sulphates formed

in (a). [7 marks]

(c) The solubility product, K sp, of magnesium hydroxide has a numerical value

of 2.0 × 10-11.

(i) Write an expression for the K sp of magnesium hydroxide, stating its

unit.

(ii) Use the value of K sp given to calculate the concentration of Mg(OH)2

in a saturated solution.

(iii) Explain whether magnesium hydroxide would be more soluble or less

soluble in 0.1 mol dm-3 MgSO4(aq) than in water. [5 marks]

Johor 09


30/44


- 30 -

5 (a) (i) Define the term standard electrode potential. [1 mark ]

(ii) Using the Data Booklet, state the cell diagrams and the standard

electrode potential values for the following reactions. [4 marks]

Fe(s) + Pb2+(aq) Fe2+(aq) + Pb(s)

2H+(aq) + Zn(s) Zn2+(aq) + H2(g)

(b) Predict the product that would be obtained from the electrolysis of the

following aqueous solutions using platinum electrodes.

(i) Copper(II) chloride

(ii) Hydrochloric acid

(iii) Potassium hydroxide [6 marks]

(c) An industrially important source of hydrogen is the reaction below.

CH4(g) + 2H2O(g) ⇌ CO2(g) + 4H2(g)

Use the enthalpy changes of combustion given below to construct an energy

cycle and use it to calculate the enthalpy change of this reaction. [4 marks]

Substance Enthalpy change of combustion, Hc / kJ mol-1

CH4 −890

H2 −242

CO2 −283

Johor 10

6 (a) Discuss, with equations, what happens in each of the experiments below.

(i) Aluminium chloride is added to water containing a few drops of

methyl orange indicator.

(ii) A strong alkali is boiled vigorously in an aluminium pot. [7 marks]

(b) Give two uses of aluminium and relate the uses to its properties. [4 marks]

(c) Explain why an aqueous solution of ammonia does not contain NH4OH

molecule. [2 marks]

(d ) Write an equation to show the role of ammonia as

(i) base

(ii) complexing agent [2 marks]

Johor 10


31/44


- 31 -

7 (a) The standard electrode potentials, for a number of electrodes are given

in the table below.

Electrode / V

Al3+

(aq) + 3e-

⇌ Al(s) -1.66Br 2(l) + 2e

- ⇌ 2Br -(aq) +1.07

Fe3+(aq) + 3e- ⇌ Fe(s) -0.04

Cu2+(aq) + 2e- ⇌ Cu(s) +0.34

Zn2+(aq) + 2e- ⇌ Zn(s) -0.76

(i) By using the data above, identify the strongest oxidising agent and

the strongest reducing agent. [2 marks](ii) Describe what you would observe when zinc powder is added to

aqueous bromine solution. [2 marks]

(iii) Calculate the e.m.f of the following electrochemical cell at 25oC.

Al(s) / Al3+(aq, 0.8 mol dm-3) // Cu2+(aq, 0.4 mol dm-3) / Cu(s)

[4 marks]

(iv) What is the effect on the e.m.f of the electrochemical cell in (a)(iii)

when the concentration of Cu2+ ions in the copper half-cell increases? [1 mark ]

(b) (i) Explain standard enthalpy change of formation of MnO2. [2 marks]

(ii) Using the data given below, calculate the enthalpy change of the

following reaction.

3MnO2(s) + 4Al(s) 2Al2O3(s) + 3Mn(s)

Enthalpy change of formation of Al2O3 = -1670 kJ mol-1

Enthalpy change of formation of MnO2 = -520 kJ mol-1

[2 marks]

(iii) Explain why this reaction is used to extract manganese from its ore,

MnO2. [2 marks]

Kedah 09


32/44


- 32 -

8 (a) Oxides of the Period 3 elements include the following:

Al2O3, SiO2, P4O6

(i) The melting points of Al2O3, SiO2 and P4O6 are 2040oC, 1610oC and

24oC respectively. Explain the differences in their melting points in terms of structure

and bonding. [6 marks]

(ii) Describe the solubilities of the oxides in water and write balanced

equations for the reaction of the oxides (if any) with water. [4 marks]

(b) Montmorillonite is a type of silicate clay which cracks during dry season.

(i) Draw the basic three dimensional structure of a silicate ion.

[1 mark ]

(ii) Draw a simple diagram to show the layered structure of

montmorillonite. [2 marks]

(iii) Explain how these cracks appear when the wet clay dries out.

[2 marks]

Kedah 09

9 (a) 2000 cm3 of a gaseous oxide of nitrogen, NxOy, reacted with pre-heated

copper powder. The reaction produced 1000 cm3 of nitrogen gas and the mass of copper

is found to have increased by 2.71 g. All volume of gases are measured at room

temperature and pressure. [Molar gas volume = 24400 cm3]

(i) Write a balanced equation for the reaction. [1 mark ]

(ii) Determine the formula of NxOy. [3 marks]

(iii) Name the dimer of this oxide of nitrogen. [1 mark ]

(b) Arrange the acids HCl, HBr and HI in increasing order of acid strength.

Explain your answer. [4 marks]

(c) [CrCl2(C2O4)2]3- is a complex ion.

(i) Name this complex ion. [1 mark ]

(ii) Draw all the structural formulae of the isomers of this complex ion.

[3 marks]

(iii) State the types of isomerism exhibited by the isomers. [2 marks]

Kedah 09


33/44


- 33 -

10 (a) The e.m.f of an electrochemical cell that involves the reaction aA + bB ⇌

cC + d D is given by the equation below

=

−0.059

log

[][]

[][]

with E cell as the standard cell potential and n as the number of moles of

electrons transferred in the reaction.

(i) Using standard electrode potentials from the data booklet and the

information given above, calculate the equilibrium constant, K c for the following

reaction. [5 marks]

Zn(s) + Cu2+(aq) ⇌ Cu(s) + Zn2+(aq)

(ii) Calculate the e.m.f of the following electrochemical cell. [2 marks]

Zn(s) / Zn2+(aq, 0.8 mol dm-3) // Cu2+(aq, 0.4 mol dm-3) / Cu(s)

(b) One method of preparing sulphur dioxide in the laboratory is by mixing

excess acid with an aqueous solution of sodium sulphite. Use the following data to

calculate the enthalpy change of this reaction. [3 marks]

H / kJ mol-1

H2(g) + S(s) +3

2O2(g) 2H

+(aq) + SO32-(aq) -623

S(s) + O2(g) SO

2(g) -296

H2(g) +1

2O2(g) H2O(l) -286

(c) The following data are about chlorine.

Enthalpy change of atomisation, H1 = +121 kJ mol-1

Electron affinity, H2 = -364 kJ mol-1

Enthalpy change of hydration, H3 = -381 kJ mol-1

By drawing an energy cycle, calculate the enthalpy change for the reaction

below, H4.

1

2Cl2(g) + water + e

- Cl-(aq)

Deduce the strength of chlorine as an oxidising agent based on the value of

H4 obtained. [5 marks]

Kedah 10


34/44


- 34 -

11 (a) Group 2 elements form carbonates, MCO3. Explain the thermal stability of

the carbonates descending the group. [5 marks]

(b) Aluminium is one widely used metal in industry. Aluminium is extracted

mainly from pure bauxite, Al2O3.

(i) Describe the extraction of aluminium from pure bauxite. [4 marks]

(ii) State one reason why aluminium metal is widely used in aerospace

industry. [1 mark]

(c) When some sodium carbonate is added into aqueous aluminium sulphate, a

colourless gas that turns lime water chalky is evolved. Explain the above observation

and write all the equations involved. [5 marks]

Kedah 10

12 (a) Nitrogen monoxide is found in exhaust gases of motorised vehicles. A

catalytic converter removes this gas from the exhaust. By using suitable chemical

equations, explain the formation of nitrogen monoxide in the engine and how the gas is

removed. [3 marks]

(b) No visible change is recorded when a heated glass rod is placed in a gas jar

containing hydrogen chloride vapour. However, a purple vapour formed when it is

placed in another gas jar containing hydrogen iodide vapour. Explain these observations.

[3 marks]

(c) A neutral, coloured compound, Q, has the empirical formula Co(Cl) x(NH3) y.

The percentage by mass of each element in the complex is as follow.

Co = 23.52% N = 28.00% Cl = 42.53%

(i) Given the relative molecular mass of Q is 250.4. Determine the

molecular formula of Q. [4 marks]

(ii) It is found that one mole of Q reacts with two moles of silver nitrate.

Determine the structural formula of Q. [1 mark ]

(iii) Explain why Q is coloured. [4 marks]

Kedah 10


35/44


- 35 -

13 (a) Define the standard formation and lattice energy of sodium chloride

crystalline. [4 marks]

(b) The possible fluorides formed by an element M are MF and MF2.

Enthalpy of atomisation of M = +284.6 kJ mol-1

First ionisation energy of M = +731.0 kJ mol-1

Second ionisation energy of M = +2073 kJ mol-1

Enthalpy of atomisation of F = +79.0 kJ mol-1

Electron affinity of F = -322.0 kJ mol-1

Lattice formation energy of MF = -969.0 kJ mol-1

Lattice formation energy of MF2 = -2260 kJ mol-1

Using the data provided above,

(i) draw a Born-Haber cycle for the formation of MF. [6 marks]

(ii) calculate the enthalpy of formation of MF. [2 marks]

(iii) if the enthalpy of formation of MF2 is +342.6 kJ mol-1, which

compound will most probably be formed when M reacts with F. Explain. [3 marks]

Kelantan 09

14 (a) Explain the term transition element . [1 mark ]

(b) Transition element complexes are often coloured whereas compounds of

other metals are usually white. For example, a solution of [Cu(H2O)6]2+ complex ion is

blue but a solution of [CuCl2]- complex ion is colourless. Explain these observations in

terms of electronic configurations. [5 marks]

(c) (i) Carbon, silicon, germanium, tin and lead are elements in Group 14 of

the Periodic Table. Describe the variation in acid-base character of their oxides.

[5 marks]

(ii) Lead(IV) oxide is a dark-brown solid. When lead(IV) oxide is heated

with an aqueous solution of a manganese(II) salt in the presence of excess nitric(V)

acid, the reaction that takes place is as follows:

2Mn2+ + 4H+ + 5PbO2 2MnO4- + 5Pb2+ + 2H2O

Explain how lead(IV) oxide reacts, and state the observations.

[4 marks]

Ktan 09


36/44


- 36 -

15 (a) 1.00 g of solid potassium hydroxide was dropped into 50.0 cm3 (50.0 g) of

aqueous hydrogen chloride (slightly in excess) contained in a polystyrene cup. A

temperature change from 30.0oC to 40.0oC was recorded. [Specific heat capacity of the

solution = 4.0 J K -1 g-1]

(i) Define the heat of neutralisation. [2 marks]

(ii) Write a balanced equation for the above reaction. [1 mark ]

(iii) From the data provided, calculate the H for the reaction. [3 marks]

(iv) Give one important reason why it is preferable to use a polystyrene

cup over a glass beaker. [1 mark ]

(v) Why should the solution be stirred during the reaction? [1 mark ]

(b) Octane, C8H18 is used as a fuel.

(i) Define the heat of combustion with respect to octane. [1 mark ]

(ii) Write a balanced equation for the combustion of octane in excess

oxygen. [1 mark ]

(iii) Calculate the standard enthalpy of combustion of octane by using the

following information. [3 marks]

H f of CO2 = −394 kJ mol-1

H f of H2O = −286 kJ mol-1

H f of C8H18 = −250 kJ mol-1

(iv) How is the knowledge of standard enthalpy of combustion useful to

a chemist other than that as a fuel? [2 marks]

Ktan 12

16 (a) Why does cobalt shows variable oxidation states? [3 marks]

(b) Explain the term complex ion. [4 marks]

(c) A complex compound, triaminetrichlorocobalt(III) exists as two isomers.

(i) What is the chemical formula of triaminetrichlorocobalt(III)?

(ii) Draw the structures of the two isomers and name them. State the type

of isomerism shown.

(iii) Explain what happens when an aqueous solution of silver nitrate is

added to an aqueous solution of triaminetrichlorocobalt(III). [8 marks]

Melaka 09


37/44


- 37 -

17 (a) Explain how the following changes down Group 2 (beryllium to barium) of

the Periodic Table. Write equations for the reactions involved.

(i) Reactivity towards water. [3 marks]

(ii) Thermal stability of the nitrates. [5 marks]

(b) Some properties of two substances X and Y are given below. Identify each

of these substances and explain the chemistry of the reactions involved.

(i) X is a colourless aqueous solution that leaves no residue on

evaporation. It forms a blue solid with an aqueous solution of copper(II) ions, and upon

excess turns into a deep blue solution. [4 marks]

(ii) Y is a compound of Group 14 elements, which exists as a colourless

liquid at room temperature. It is stable to heat even at high temperature. It reacts with

water to form an acidic solution. [3 marks]

Melaka 09

18 (a) 0.500 g of solid aluminium chloride was heated to 200oC at a pressure of

1.00 × 105 Pa. The volume of vapour formed at this temperature and pressure was

found to be 73.6 cm3. Calculate the relative molecular mass of the vapour at this

temperature and pressure. Draw a displayed formula to show the types of bonding in

the molecules of the vapour. [4 marks]

(b) Explain with the help of equations why an aqueous solution of aluminium

sulphate has a pH of 4.8. [3 marks]

(c) Carbon and silicon are the first two elements in Group 14 of the Periodic

Table. Carbon dioxide is a gas that dissolves in and reacts with water. Silicon(IV) oxide

is a solid that is insoluble and unreactive towards water. The tetrachlorides of carbon

and silicon are both liquids, one of which reacts with water and the other does not.

Explain the differences in physical and chemical properties of these four compounds

described by these statements. Write balanced equations for all reactions that occur.

[8 marks]

NS 09


38/44


- 38 -

19 (a) How do chloride, bromide and iodide ions differ in their reactions with

(i) silver nitrate solution, followed by aqueous ammonia.

(ii) concentrated sulphuric acid.

In each case, suggest the products of the reaction and write equations where

appropriate. [9 marks]

(b) What do you understand by the term transition element ? State two

properties of iron or its compounds that typify it as a transition element. [3 marks]

(c) Describe and explain what happens when an aqueous solution containing

Cu2+ ions is added gradually with dilute aqueous ammonia followed by an aqueous

solution of [EDTA]4-. [3 marks]

NS 09

20 (a) Oxides of Period 3 elements are classified as basic, amphoteric and acidic.

Describe the reactions of Period 3 elements with oxygen to form the above types of

oxide. [7 marks]

(b) The table below gives the standard reduction potentials, E o for Group 2

elements.

Element Be Mg Ca Sr Ba

E o / V −1.85 −2.38 −2.87 −2.89 −2.90

Explain the reactivity of Group 2 elements towards water by referring to

the above standard reduction potential values. [4 marks]

(c) State and explain the thermal stability of the nitrates when descending

Group 2 of the Periodic Table. [4 marks]

NS 2010

21 (a) (i) What do you understand by anodizing of aluminium?

(ii) Describe the method used to carry out this process. Explain the

chemistry involved with the aid of balanced equations. [7 marks]

(b) State and explain the thermal stability of Group 14 tetrachlorides from

carbon to lead. [4 marks]

(c) (i) Name one tetrachloride of Group 14 that does not react with water

and explain why.

(ii) Name one tetrachloride of Group 14 that reacts with water and write

an equation for the reaction. [4 marks]


39/44


- 39 -

22 (a) Explain why the reaction between sodium halides with concentrated

sulphuric acid can be used to prepare bromine but not chlorine. [4 marks]

(b) The elements scandium, manganese and zinc are first row d -block elements

in the Periodic Table.

(i) Write the electronic configurations for the ions Sc3+, Mn2+ and Zn2+.

(ii) Which of the above ion(s) is / are colourless. Explain. [5 marks]

(c) A typical property of transition elements is their ability to form complexes.

A complex of chromium has the formula [Cr(NH3)6]3+.

(i) Explain how the [Cr(NH3)6]3+ ion can be prepared from aqueous

chromium(III) chloride.

(ii) Explain why Cr 3+ ions have a great tendency to form such complexes.

(iii) Another complex of chromium has the formula [CrCl2(NH3)4]+. Draw

the structural formulae for the two isomers of this complex. [6 marks]

nS11

23 (a) The ore of aluminium is bauxite.

(i) Briefly describe the extraction of aluminium from pure bauxite.

(ii) Explain the use of aluminium in aircraft construction. [7 marks]

(b) Aluminium, silicon, phosphorus and sulphur are Period 3 elements in the

Periodic Table. The melting points of the elements are given below.

Element Melting point ( oC)

Aluminium 660

Silicon 1410

Phosphorus 44

Sulphur 119

Explain the melting points of the elements in terms of structure and bonding.

[8 marks]

Pahang 09


40/44


- 40 -

24 (a) Explain why chlorine is used in the large scale preparation of bromine from

sea water which contains bromide ions. [4 marks]

(b) Explain why iodine is more soluble in potassium iodide solution than in

water. Write balanced equations for any reactions that occur. [4 marks]

(c) How does sodium chloride reacts with concentrated sulphuric acid? State

the conditions for which the reaction can occur. Write balanced equations for the

reactions that occur. [4 marks]

(d ) Explain what happens when solid potassium iodide is heated with

concentrated sulphuric acid. [3 marks]

Phg 09

25 (a) A solution of sodium chloride of concentration 2.00 mol dm-3 is

electrolysed for 25 minutes using graphite electrodes. The resulting solution is then

treated with hydrochloric acid of concentration 0.25 mol dm-3. If the volume of

hydrochloric acid needed to complete the titration is 15.50 cm3, calculate the magnitude

of the current used during the electrolysis. [7 marks]

(b) Passing air through an aqueous solution containing CoCl2,

H2 N(CH2)CH2 NH2 and HCl produces a green complex cation, Y, with formula

[Co(H2 NCH2CH2 NH2)2Cl2]+. Evaporation of an aqueous solution of Y at 90oC

produces a red complex cation, Z, with the same formula as Y. Y has no dipole moment,

whereas Z has.

(i) Draw all isomers with the formula [Co(H2 NCH2CH2 NH2)2Cl2]+.

(ii) Which of the isomers could be the structure of Y and Z? Give your

reason. [5 marks]

(c) Magnesium carbonate undergoes thermal decomposition at a much lower

temperature (353oC) than barium carbonate (1430oC). Explain in terms of structure and

bonding. [3 marks]

Phg 10 + Johor 08


41/44


- 41 -

26 (a) By referring to the physical and chemical properties of aluminium, describe

the property of an aqueous solution of aluminium salt. [5 marks]

(b) By writing equations for the reactions involved, explain

(i) the reaction of anhydrous aluminium chloride with water. [2 marks]

(ii) why aluminium carbonate cannot be prepared from a solution

containing Al3+ ions. [4 marks]

(iii) Aluminium chloride is a white solid which fumes in moist air and

sublimes at 180oC. [4 marks]

Phg 10

27 (a) State the changes in acid-base properties of oxides of Period 3 elements,

from sodium to chlorine in the Periodic Table. Write an equation to represent each

typical property of the oxides. [6 marks]

(b) Between hydrogen chloride and hydrogen sulphide, which is the stronger

acid in aqueous solution? Explain your answer. [4 marks]

(c) Draw the possible structures of isomers of the following complexes. State

the name of each isomer.

(i) [Cr(NH3)4Cl2]+

(ii) [Cr(C2O4)3]3- [5 marks]

Phg 11

28 (a) Oxides of the Period 3 elements include the following:

Al2O3, SiO2, P4O6

(i) The melting points of Al2O3, SiO2 and P4O6 are 2040oC, 1610oC and

24oC respectively. Explain the differences in their melting points in terms of structure

and bonding. [6 marks]

(ii) Describe the solubilities of the oxides in water and write balanced

equations for the reaction of the oxides (if any) with water. [4 marks]

(b) Montmorillonite is a type of silicate clay which cracks during dry season.

(i) Draw the basic three dimensional structure of a silicate ion.

[1 mark ]

(ii) Draw a simple diagram to show the layered structure of

montmorillonite. [2 marks]

(iii) Explain how these cracks appear when the wet clay dries out.

[2 marks]


42/44


- 42 -

29 (a) Platinum(II) forms square planar complexes such as [Pt(NH3)2Cl2] while

platinum(IV) forms octahedral complexes such as [Pt(NH3)4ClBr]2+.

(i) Explain what is meant by complex ion. [2 marks]

(ii) Give the IUPAC name of [Pt(NH3)2Cl2] and [Pt(NH3)4ClBr]2+.

[2 marks]

(iii) Both these complexes exhibit geometrical isomerism. Draw the trans-

isomer for both of them. [2 marks]

(b) A neutral compound, H has the empirical formula Co(Cl)x(NH3)y. The

percentage by mass of cobalt, nitrogen and chlorine is as follow:

Co = 23.52% ; N = 28.00% ; Cl = 42.53%

When an aqueous solution containing 12.52 g of H is reacted with excess

AgNO3 solution, 14.53 g of silver chloride is precipitated. Deduce the structural

formula of the complex. Explain if you expect H to be coloured. [9 marks]

Phg 12

30 (a) Describe and explain the variation in boiling point of the tetrachlorides of

Group 14 elements, from carbon to lead. [4 marks]

(b) How and why do CCl4 and SiCl4 differ in their reactions with water?

Include in your answer any reactions that occur. [4 marks]

(c) Suggest a use of each element or compound below, and explain how each

of the uses is related to physical or chemical properties and structure.

(i) Silicon

(ii) Silicon(IV) oxide

(iii) Carbon dioxide [3 marks]

(d ) Aluminium is extracted from a mixture of molten aluminium oxide and

cryolite, Na3AlF6 by electrolysis. Suggest factors that have to be taken into

consideration when choosing a site for an aluminium factory. State one adverse effect

on the environment as a result of the extraction process of aluminium. [4 marks]

Trg -09


43/44


- 43 -

31 (a) White precipitate is formed when aqueous ammonia is added to aqueous

magnesium chloride. The white precipitate dissolves when excess ammonium chloride

is added to the mixture. Explain the observations. [4 marks]

(b) Given the following standard enthalpies of combustion:

H c of C(s) = −393 kJ mol-1

H c of H2(g) = −285.6 kJ mol-1

H c of C8H18(l) = −5512 kJ mol-1

Define standard enthalpy of formation of octane, C8H18(l) and determine its

value. [4 marks]

(c) The lattice enthalpy of rubidium chloride, RbCl can be determined

indirectly using Born-Haber cycle. Given the data below, construct the cycle and

determine the lattice enthalpy of rubidium chloride.

Enthalpy change of formation of RbCl = −435 kJ mol-1

Enthalpy change of atomisation of Rb = +81 kJ mol-1

Enthalpy change of atomisation of Cl = +122 kJ mol-1

First ionization energy of Rb = +403 kJ mol-1

First electron affinity of Cl = −349 kJ mol-1

Explain why the lattice enthalpy of lithium chloride is more exothermic

than that of rubidium chloride. [7 marks]

Sam tet

32 (a) State two different substances in everyday or industrial use that contain

chlorine. For each of these substances, state its use and explain briefly how the use is

related to the property of the substance. [6 marks]

(b) Explain the stability trend of the +2 and +3 oxidation states for the transition

elements. [3 marks]

(c) What do you understand by the term transition element and explain why

scandium and zinc are not transition elements. [6 marks]

Trg 10

END OF QUESTIONS


44/44


chem+sem+2+str

Documents

Transcript of chem+sem+2+str