STPM Chemistry Semester 2 1 STPM CHEM
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.
E = +0.17 V CrO 4 2-
SO o 4 (aq) + 4H (aq) + 2e ⇌ 2H
2 O(l) + SO 2 (g)
2 O(l) + Cr 3+ (aq) E = +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]
(aq) + 8H o + (aq) + 3e ⇌ 4H
(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) + Cl 2 (g)
Li(g) + Cl 2 (g)
Li(s) + Cl 2 (g) H 6
Li + Cl - (s)
(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]
[1 mark] .......................................................................................................................................... Trg 2010
(iii) Comment on the solubility of lithium chloride in water.
4 (a) Refer to the data given below for questions 4(a)(i) – (ii).
o H 2 O 2 + 2H + 2e ⇌ 2H
E red = 1.776 V
o H 2 O 2 + 2e ⇌ 2OH E red = 0.88 V
o MnO 4 + 8H + 5e ⇌ Mn + 4H
2+
E red = 1.491 V
2 + 4OH E 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.
o MnO 4 + 2H 2 O + 3e ⇌ MnO
[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]
(b) The table below shows the data about the carbonates of Group 2 elements. Compound
BeCO 3 MgCO 3 CaCO 3 BaCO 3 Decomposition
1360 temperature ( o C)
540
900
(i) Predict T. [1 mark] .......................................................................................................................................... (ii) Explain the trend in decomposition by heat of Group 2 carbonates. [2 marks] .......................................................................................................................................... ..........................................................................................................................................
SMJKST
13 (a) The yellow gas, chlorine dioxide, ClO 2 , has been used for many years as flour-improving agent in bread making. It can be made in the laboratory by the following reaction.
2AgClO 3 (s) + Cl 2 (g) 2AgCl(s) + 2ClO 2 (g) + O 2 (g)
H = 0 kJ
[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.
(i) Give the oxidation state of Cl in ClO 2 .
[1 mark] .......................................................................................................................................... (iii) Given that the standard enthalpies of formation of AgClO 3 and AgCl
are -1 −25 kJ mol and −127 kJ mol respectively. Calculate and comment on the value of the standard enthalpy of formation of chlorine dioxide.
(b) The standard electrode potentials of the following systems are given below. o System E /V
- ClO
+1.50 + S(s) + 2H (aq) + 2e ⇌ H
2 (aq) + 4H (aq) + 5e ⇌ Cl (aq) + 2H 2 O(l)
+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.
2 S(aq)
[4 marks]
Melaka 2009
14 Several standard electrode potentials are shown below.
o Half-cell E /V
⇌ Cl - +1.36
Fe 2+ +e ⇌ Fe +0.77
I 2 +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]
3+ (b) Chlorine will oxidises Fe to Fe but iodine does not. Explain why by using the electrode potentials data.
2+
[2 marks] .......................................................................................................................................... .......................................................................................................................................... ..........................................................................................................................................
Kelantan 12
21 Consider the incomplete Born-Haber cycle and the table of data below.
- Ca (g) + 2Cl (g) ..........................................
Ca(s) + Cl 2 (g)
CaCl 2 (s)
Standard enthalpy change -1 Value / kJ mol Enthalpy of atomisation of Cl
Enthalpy of atomisation of Ca
First ionization energy of Ca
Second ionization energy of Ca
Electron affinity of Cl
−364 Lattice energy of CaCl 2 −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]
- (c) The standard enthalpies of hydration of the Ca and Cl ions are −1650 kJ mol -1 and
2+
−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, NH 4 Cl 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 20 o
C. Calculate the temperature change and the final temperature of the solution. Assume that the specific heat capacity of the solution is 4.2
-1 JK -1 g . [3 marks]
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) | Cu 2+ (aq) || Fe 3+ (aq) , Fe 2+ (aq) | Pt(s) o and calculate the standard electrode potential, E , 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 15 o C to 65
C. 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 -1 = −393.5 kJ mol Enthalpy change of combustion of H -1 = −285.8 kJ mol
[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
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 -11 × 10 . (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 MgSO
4 (aq) than in water.
[5 marks]
Johor 09
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) + Pb 2+ (aq) Fe (aq) + Pb(s)
2H 2+ (aq) + Zn(s) Zn (aq) + H
2 (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. CH 4 (g) + 2H 2 O(g) ⇌ CO 2 (g) + 4H 2 (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, H c / kJ mol -1
CH 4 −890
H 2 −242 CO 2 −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 NH 4 OH molecule.
[2 marks] (d) Write an equation to show the role of ammonia as (i) base (ii) complexing agent
[2 marks] Johor 10
7 (a) The standard electrode potentials, 𝐸 𝜃 for a number of electrodes are given in the table below.
Al - (aq) + 3e ⇌ Al(s) -1.66
Br 2 (l) + 2e - ⇌ 2Br - (aq)
Fe - (aq) + 3e ⇌ Fe(s) -0.04 Cu 2+ (aq) + 2e - ⇌ Cu(s) +0.34
Zn - (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] o (iii) Calculate the e.m.f of the following electrochemical cell at 25 C.
Al(s) / Al -3 (aq, 0.8 mol dm ) // Cu (aq, 0.4 mol dm ) / 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 Cu 2+ ions in the copper half-cell increases? [1 mark] (b) (i) Explain standard enthalpy change of formation of MnO 2 . [2 marks] (ii) Using the data given below, calculate the enthalpy change of the following reaction.
3MnO 2 (s) + 4Al(s) 2Al 2 O 3 (s) + 3Mn(s)
-1 Enthalpy change of formation of Al
2 O 3 = -1670 kJ mol Enthalpy change of formation of MnO 2 = -520 kJ mol -1
[2 marks] (iii) Explain why this reaction is used to extract manganese from its ore, MnO 2 .
[2 marks]
Kedah 09
8 (a) Oxides of the Period 3 elements include the following:
Al 2 O 3 , SiO 2 ,P 4 O 6
(i) The melting points of Al 2 O 3 , SiO 2 and P 4 O 6 are 2040 o
C, 1610 o C and
24 o C 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 cm 3 of a gaseous oxide of nitrogen, N x O y , reacted with pre-heated copper powder. The reaction produced 1000 cm 3 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 cm 3 ]
(i) Write a balanced equation for the reaction. [1 mark] (ii) Determine the formula of N x O y .
[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) [CrCl 2 (C 2 O 4 ) 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
10 (a) The e.m.f of an electrochemical cell that involves the reaction aA + bB ⇌
c C + dD is given by the equation below
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) + Cu 2+ (aq)
⇌ Cu(s) + Zn 2+ (aq)
(ii) Calculate the e.m.f of the following electrochemical cell. [2 marks]
Zn(s) / Zn -3 (aq, 0.8 mol dm ) // Cu (aq, 0.4 mol dm ) / 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] -1 H / kJ mol
2- H
2 (g) + S(s) + O 2 (g) 2H (aq) + SO 3 (aq)
S(s) + O 2 (g) SO 2 (g)
H 2 (g) + O 2 (g) H 2 O(l)
(c) The following data are about chlorine. -1 Enthalpy change of atomisation, H 1 = +121 kJ mol
2 = -364 kJ mol -1 Enthalpy change of hydration, H
-1 Electron affinity, H
3 = -381 kJ mol By drawing an energy cycle, calculate the enthalpy change for the reaction below, H 4 .
Cl -
2 (g) + water + e Cl (aq)
Deduce the strength of chlorine as an oxidising agent based on the value of H 4 obtained.
[5 marks]
Kedah 10
11 (a) Group 2 elements form carbonates, MCO 3 . 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, Al 2 O 3 .
(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 (NH 3 ) y . The percentage by mass of each element in the complex is as follow. Co = 23.52%
Cl = 42.53% (i) Given the relative molecular mass of Q is 250.4. Determine the molecular formula of Q.
N = 28.00%
[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
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 MF 2 .
-1 Enthalpy of atomisation of M = +284.6 kJ mol -1 First ionisation energy of M = +731.0 kJ mol Second ionisation energy of M
= +2073 kJ mol -1
Enthalpy of atomisation of F
= +79.0 kJ mol -1 -1 Electron affinity of F = -322.0 kJ mol
-1 Lattice formation energy of MF = -969.0 kJ mol
Lattice formation energy of MF 2 = -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] -1 (iii) if the enthalpy of formation of MF
2 is +342.6 kJ mol , 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(H 2 O) 6 ] 2+ complex ion is blue but a solution of [CuCl -
2 ] 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:
2Mn 2+ + 4H + + 5PbO 2 2MnO 4 - + 5Pb 2+ + 2H 2 O Explain how lead(IV) oxide reacts, and state the observations.
[4 marks] Ktan 09
15 3 (a) 1.00 g of solid potassium hydroxide was dropped into 50.0 cm (50.0 g) of aqueous hydrogen chloride (slightly in excess) contained in a polystyrene cup. A
temperature change from 30.0 o C to 40.0 o C was recorded. [Specific heat capacity of the
-1 solution = 4.0 J K -1 g ] (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, C 8 H 18 is used as a fuel.
[1 mark] (ii) Write a balanced equation for the combustion of octane in excess oxygen.
(i) Define the heat of combustion with respect to octane.
[1 mark] (iii) Calculate the standard enthalpy of combustion of octane by using the following information.
[3 marks]
−394 kJ mol -1 H f of H -1 2 O = −286 kJ mol
H f of CO 2 =
H f of C -1 8 H 18 = −250 kJ mol
(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
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
o (a) 0.500 g of solid aluminium chloride was heated to 200 C at a pressure of
1.00 5 × 10 Pa. The volume of vapour formed at this temperature and pressure was found to be 73.6 cm 3 . 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
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
Cu 2+ 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] o (b) The table below gives the standard reduction potentials, E for Group 2
elements. Element
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]
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.
2+ (i) Write the electronic configurations for the ions Sc , Mn and Zn . (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(NH 3+
3 ) 6 ] . 3+ (i) Explain how the [Cr(NH 3 ) 6 ] ion can be prepared from aqueous
chromium(III) chloride. 3+ (ii) Explain why Cr ions have a great tendency to form such complexes.
2 (NH 3 ) 4 ] . Draw the structural formulae for the two isomers of this complex.
+ (iii) Another complex of chromium has the formula [CrCl
[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 o Melting point ( C) Aluminium
Explain the melting points of the elements in terms of structure and bonding. [8 marks] Pahang 09
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
-3 (a) A solution of sodium chloride of concentration 2.00 mol dm 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 cm 3 , calculate the magnitude of the current used during the electrolysis.
[7 marks] (b) Passing air through an aqueous solution containing CoCl 2 ,
H 2 N(CH 2 )CH 2 NH 2 and HCl produces a green complex cation, Y, with formula
[Co(H o
2 NCH 2 CH 2 NH 2 ) 2 Cl 2 ] . Evaporation of an aqueous solution of Y at 90 C produces a red complex cation, Z, with the same formula as Y. Y has no dipole moment, whereas Z has.
2 NCH 2 CH 2 NH 2 ) 2 Cl 2 ] . (ii) Which of the isomers could be the structure of Y and Z? Give your reason.
+ (i) Draw all isomers with the formula [Co(H
[5 marks] (c) Magnesium carbonate undergoes thermal decomposition at a much lower temperature (353 o
C) than barium carbonate (1430 o C). Explain in terms of structure and bonding.
[3 marks]
Phg 10 + Johor 08
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 Al 3+ ions.
[4 marks] (iii) Aluminium chloride is a white solid which fumes in moist air and
sublimes at 180 o C. [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(NH 3 ) 4 Cl 2 ] +
3- (ii) [Cr(C
2 O 4 ) 3 ] [5 marks] Phg 11
28 (a) Oxides of the Period 3 elements include the following:
Al 2 O 3 , SiO 2 ,P 4 O 6
o (i) The melting points of Al
2 O 3 , SiO 2 and P 4 O 6 are 2040
C, 1610
C and
24 o C 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]
29 (a) Platinum(II) forms square planar complexes such as [Pt(NH 3 ) 2 Cl 2 ] while platinum(IV) forms octahedral complexes such as [Pt(NH 2+
3 ) 4 ClBr] . (i) Explain what is meant by complex ion.
[2 marks] 2+ (ii) Give the IUPAC name of [Pt(NH
3 ) 2 Cl 2 ] and [Pt(NH 3 ) 4 ClBr] . [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 (NH 3 ) 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 AgNO 3 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 CCl 4 and SiCl 4 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, Na 3 AlF 6 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
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:
-1 H c of C(s) = −393 kJ mol
H c -1 of H
2 (g)
= −285.6 kJ mol
H c -1 of C
8 H 18 (l)
= −5512 kJ mol
Define standard enthalpy of formation of octane, C 8 H 18 (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.
-1 Enthalpy change of formation of RbCl = −435 kJ mol -1 Enthalpy change of atomisation of Rb = +81 kJ mol Enthalpy change of atomisation of Cl = +122 kJ mol -1
-1 First ionization energy of Rb = +403 kJ mol -1 First electron affinity of Cl = −349 kJ mol
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