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-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) Eo = +0.17 V
CrO42-(aq) + 8H+(aq) + 3e ⇌ 4H2O(l) + Cr3+(aq) Eo = +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]
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(iii) What colour change takes place? [1 mark]
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(b) Li+(g) + Cl(g)
+121 Li+(g) + 12Cl2(g) −364
Li+(g) + Cl-(g)
+520
Li(g) + 1
2Cl2(g)
+159 Li(s) + 1
2Cl2(g) H6
−409
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(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]
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-(b) Nitrogen exists in the atmosphere as N2 molecules. Nitrogen is inert.
(i) Explain the inertness of nitrogen. [1 mark]
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(ii) Give two examples (other than the Haber process) of reactions
involving atmospheric nitrogen. [2 marks]
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(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]
(e) Describe how oxides of nitrogen is eliminated from the exhaust gas by the
use of a catalytic converter. [1 mark]
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-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]
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(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 Cr3+ ion. [1 mark]
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(ii) Briefly explain why the Cr3+(aq) ion is coloured. [3 marks]
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-4 (a) Refer to the data given below for questions 4(a)(i) – (ii).
H2O2 + 2H+ + 2e ⇌ 2H2O Eo
red = 1.776 V H2O2 + 2e ⇌ 2OH- Eored = 0.88 V
MnO4- + 8H+ + 5e ⇌ Mn2+ + 4H2O Eo
red = 1.491 V MnO4- + 2H2O + 3e ⇌ MnO2 + 4OH- Eo
red = 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
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-(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]
...
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-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]
(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:
(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]
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-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]
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(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]
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(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]
...
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(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]
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(ii) Write two balanced equations to explain the observations above.
[2 marks]
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-(b) The carbonates of the Group 2 elements decompose on heating.
(i) Write the chemical equation for the decomposition of magnesium
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]
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-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]
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(ii) What is the property exhibited by the hydrated beryllium ion in the
reaction above? [1 mark]
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(c) Explain briefly why beryllium ion forms covalent compounds compared to
other elements in the same group. [2 marks]
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...
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(d) Nitric(V) acid is manufactured from ammonia in the Ostwald Process.
(i) Name the catalyst used in this reaction. [1 mark]
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(ii) Write equation to show the formation of nitrogen monoxide in the
Ostwald Process. [1 mark]
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(iii) Predict qualitatively the conditions of temperature and pressure that
will give a maximum yield of nitrogen monoxide at equilibrium. [2 marks]
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-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]
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...
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(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]
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(ii) What is observed when magnesium nitrate is heated strongly?
[1 mark]
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(c) How does the solubilities of the Group 2 sulphates change when moving
down the group? Explain your answer. [3 marks]
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-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]
...
...
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(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]
...
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(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]
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-11 (a) Aqueous ammonia is added to aqueous aluminium sulphate slowly until in
excess.
(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]
(ii) State two properties of iron that enable it to form complex ions.
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-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]
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(ii) Aqueous hydrochloric acid. [1 mark]
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(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]
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(ii) Both magnesium nitrate and strontium nitrate will decompose on
heating. Which of the two will decomposes at a lower temperature? [1 mark]
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(iii) Explain your answer in (c)(ii). [2 marks]
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(d) Arrange the solubilities of Group 2 sulphates in descending order.
[1 mark]
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-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]
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(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]
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(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 Eo / 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]
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-14 Several standard electrode potentials are shown below.
Half-cell Eo / 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]
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(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
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-(b) Chlorine will oxidises Fe2+ to Fe3+ but iodine does not. Explain why by
using the electrode potentials data. [2 marks]
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...
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-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] …... …... …... …...
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-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]
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...
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(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]
...
...
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-17 (a) The standard electrode potentials, at 298 K, of some half-cells are given
below.
(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]
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(ii) State one use of optical fibre. [1 mark]
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(iii) In certain applications, optical fibres have many advantages over
copper wire. State two advantages of optical fibres over copper wire. [2 marks]
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...
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(iv) State the difference in the structure between glass and diamond.
[2 marks]
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-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]
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(ii) State one important use of aluminium chloride. [1 mark]
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(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]
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(ii) aluminium is not easily corroded as iron. [1 mark]
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(d) Write the chemical equations for the reaction of chlorine with
(i) cold aqueous sodium hydroxide. [1 mark]
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(ii) hot aqueous sodium hydroxide. [1 mark]
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-19 (a) (i) Give the definition of standard electrode potential. [2 marks]
...
...
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The standard reduction electrode potentials for several half-cell reactions at
298 K are given in the table below.
Half-cell reaction Eo / V
S2O82- + 2e 2SO42- +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, K2S2O8 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]
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-(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
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-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
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-(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
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-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]
(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]
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-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]
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(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]
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-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, Eo, 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]
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-(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, Ksp, of magnesium hydroxide has a numerical value
of 2.0 × 10-11.
(i) Write an expression for the Ksp of magnesium hydroxide, stating its
unit.
(ii) Use the value of Ksp 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]
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-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.
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-7 (a) The standard electrode potentials, 𝐸𝜃 for a number of electrodes are given
in the table below.
Electrode 𝐸𝜃 / V
Al3+(aq) + 3e- ⇌ Al(s) -1.66
Br2(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]
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-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) 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]
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-electrons transferred in the reaction.
(i) Using standard electrode potentials from the data booklet and the
information given above, calculate the equilibrium constant, Kc for the following
reaction. [5 marks]
calculate the enthalpy change of this reaction. [3 marks] H / kJ mol-1
H2(g) + S(s) + 32O2(g) 2H+(aq) + SO32-(aq) -623
S(s) + O2(g) SO2(g) -296
H2(g) + 12O2(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]
- 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.
- 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]
- 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]
(iii) Calculate the standard enthalpy of combustion of octane by using the
following information. [3 marks]
Hf of CO2 = −394 kJ mol-1 Hf of H2O = −286 kJ mol-1 Hf 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]
- 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]
- 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, Eo for Group 2
elements.
Element Be Mg Ca Sr Ba
Eo / 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
- 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 Cr3+ 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]
- 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,
H2N(CH2)CH2NH2 and HCl produces a green complex cation, Y, with formula
[Co(H2NCH2CH2NH2)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(H2NCH2CH2NH2)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]
- 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]
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.
- 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]
- 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: Hc of C(s) = −393 kJ mol-1
Hc of H2(g) = −285.6 kJ mol-1 Hcof 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
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