9.2. Periodicity of chemical properties of the elements in Period 3
A subsection of Chemistry, 9701, through 9. The Periodic Table: chemical periodicity
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Group2 metals form alkaline solutions in water. Write the equation for the reaction of calcium oxide with water. Identify the ion that causes an aqueous solution to be alkaline. The table shows the melting points of some Group2 metal oxides. compound melting point / °C MgO CaO SrO BaO Explain the trend in the melting points of the oxides down Group2. Oxygen reacts readily with some metals, but each Group2 metal requires strong heating to start the reaction with oxygen. Suggest why strong heating is required to start these reactions. Berylliumoxide reacts with hydrochloricacid to form molecules of BeCl 2. Deduce the bond angle in BeCl 2.  Unlike the other oxides of Group2 metals, berylliumoxide is amphoteric. Give the meaning of the term amphoteric. Berylliumoxide and aluminiumoxide have similar chemical properties. The Be(OH)4 2– anion is a product of the reaction between berylliumoxide and excess concentrated OH–. Construct an equation for this reaction. Magnesiumoxide reacts reversibly with chlorine according to the following equation. 2MgO+ 2Cl 22MgCl 2+ O2Under certain conditions, a dynamic equilibrium is established. State two features of a reaction that is in dynamic equilibrium.  The equilibrium constant, Kp, is given by the following expression. Kp = pO2 pCl 2 At 1.00 × 105 Pa and 500 K, 70% of the initial amount of Cl 2has reacted. Calculate Kp and state its units.  Kp =  units =  Magnesiumperoxide, MgO2, is made in the following reaction. MgO+ H2O2MgO2+ H2O∆H = –96 kJ mol–1 compound enthalpy change of formation, ∆Hf / kJ mol–1 MgO–602 H2O2–188 H2O–286 The peroxide ion is O2 2–. Deduce the average oxidation number of oxygen in the peroxide ion. Define the term enthalpy change of formation. Use the data given to calculate the enthalpy change of formation of MgO2. ∆Hf MgO2= kJ mol–1 Magnesium peroxide decomposes slowly to form magnesium oxide and oxygen. MgO2MgO+ 2O2Use your answer to and the data in the table to calculate the enthalpy change of this reaction. If you were unable to obtain an answer to , use the value ∆Hf = –550 kJ mol–1. This is not the correct answer.  enthalpy change of reaction = kJ mol–1 
9701_m20_qp_22
THEORY
2020
Paper 2, Variant 2
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Iron(compounds are generally only stable in neutral, non-oxidising conditions. It is difficult to determine the lattice energy of FeO experimentally. Use data from the Data Booklet and this Born–Haber cycle to calculate the lattice energy, ∆H latt, of FeOin kJ mol–1. Fe2++ O+ 2e– Fe2++ O–+ e– Fe++ O+ e– Fe+ OFeOFe2++ O2–Fe+ 2O21 Fe+ 2O21 –141 kJ mol–1 –272 kJ mol–1 +798 kJ mol–1 +416 kJ mol–1 H latt  ∆H lattFeO= kJ mol–1 Most naturally occurring samples of iron(oxide are found as the mineral wüstite. Wüstite has formula Fe20Ox. It contains both Fe2+ and Fe3+ ions. 90% of the iron is present as Fe2+ and 10% is present as Fe3+. Deduce the value of x.  x = State and explain how the lattice energy of FeOcompares to the lattice energy of CaO. Heating of FeO results in the formation of Fe3O4, as shown. reaction 1 4FeO → Fe + Fe3O4 Each formula unit of Fe3O4 contains one Fe2+ and two Fe3+ ions. Show how reaction1 can be described as a disproportionation reaction. Fe3O4can be electrolysed using inert electrodes to form Fe. Write the half-equation for the reaction that occurs at the anode during the electrolysis of Fe3O4. Calculate the maximum mass of iron metal formed when Fe3O4is electrolysed for sixhours using a current of 50 A. Assume the one Fe2+ and two Fe3+ ions are discharged at the same rate.  mass of iron = g LiFePO4 can be used in lithium-ion rechargeable batteries. When the cell is charging, lithium reacts with a graphite electrode to form LiC6. When the cell is discharging, the half-equations for the two processes that occur are as follows. anode half-equation LiC6 → 6C + Li+ + e– cathode half-equation Li+ + FePO4 + e– → LiFePO4 State one possible advantage of developing cells such as lithium-ion rechargeable batteries. Use the cathode half-equation to determine the change, if any, in oxidation states of lithium and iron at the cathode during discharging. metal change in oxidation state during discharging from to lithium iron  Write the equation for the overall reaction that occurs when this cell is discharging. 
9701_m21_qp_42
THEORY
2021
Paper 4, Variant 2
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Some oxides of elements in Period3 are shown. Na2O Al 2O3 P4O6 P4O10 SO2 SO3 Na reacts with O2 to form Na2O. Na is the reducing agent in this reaction. Define reducing agent. Write an equation for the reaction of Na2O with water. Al 2O3 is an amphoteric oxide found in bauxite. State what is meant by amphoteric. Al 2O3 is purified from bauxite in several steps. The first step involves heating Al 2O3 with an excess of NaOH. A colourless solution forms. Write an equation for this reaction. Al 2O3 is used as a catalyst in the dehydration of alcohols. State the effect of using Al 2O3 as a catalyst in the dehydration of alcohols. Use the Boltzmann distribution in Fig.2.1 to help explain your answer. energy number of molecules P4O6 is a white solid that has a melting point of 24 °C. Solid P4O6 reacts with water to form H3PO3. Deduce the type of structure and bonding shown by P4O6. Explain your answer. Determine the oxidation number of P in H3PO3. When P4O6is heated with oxygen it forms P4O10. P4O6+ 2O2→ P4O10∆Hr = –1372 kJ mol–1 The enthalpy change of formation, ∆Hf, of P4O10is –3012 kJ mol–1. Calculate the enthalpy change of formation, ∆Hf, of P4O6. ∆Hf of P4O6= kJ mol–1 Write an equation for the reaction of P4O10 with water. SO2 and SO3 are found in the atmosphere. The oxidation of SO2 to SO3 in the atmosphere is catalysed by NO2. The first step of the catalytic oxidation is shown in equation1. equation 1 SO2+ NO2SO3+ NOConstruct an equation to show how NO2 is regenerated in the catalytic oxidation of SO2. NO2 can also react with unburned hydrocarbons to form photochemical smog. State the product of this reaction that contributes to photochemical smog. Fig.2.2 shows how the temperature of the atmosphere varies with height from the ground. –120 –100 –80 –60 –40 temperature / C –20 height / km The equilibrium reaction in equation1 has ∆Hr = –168 kJ mol–1. Suggest how the position of this equilibrium differs at a height of 20 km compared with a height of 50 km from the ground. Explain your answer. 
9701_m22_qp_22
THEORY
2022
Paper 2, Variant 2
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Titanium is a transition element in Period4. It is commonly found as TiO2 in minerals. Define transition element. Identify two typical properties of transition elements.  The TiO2+ ion forms when TiO2 reacts with an excess of sulfuric acid. TiO2+ can be reduced by zinc metal in acidic conditions to form a purple solution containing Ti3+. TiO2+is a colourless ion. Suggest why. Give the electronic configuration of an isolated Ti3+ ion. 1s2 ��������������������������������������������������������������������������������������������������������������������������������� Write an ionic equation for the reduction of TiO2+ by zinc metal in acidic conditions. Acidified Ti3+reacts with oxygen dissolved in water as shown. 4Ti3+ + O2 + 2H2O → 4TiO2+ + 4H+ ∆G o = –436.1 kJ mol–1 The standard reduction potential, E o, of O2 + 4H+ + 4e– 2H2O is +1.23 V. Calculate the standard reduction potential, E o, in V, of the TiO2+/ Ti3+half-cell. Show your working.  E o = V When aqueous citrate ions, C6H5O7 3–, are added to Ti3+, the [Ti(C6H5O7)2]3–complex forms. Explain, in terms of d-orbitals, why Ti3+ is able to form complex ions. Acidified [Ti(C6H5O7)2]3–does not react with oxygen dissolved in water, unlike acidified Ti3+. Suggest what this means for the value of the standard reduction potential, E o, of the following half‑cell. [Ti(C6H5O7)2]2–+ e– [Ti(C6H5O7)2]3–Explain your answer. Some reactions of TiO2 are shown in Fig.3.1. The anion, acac–, is a bidentate ligand. TiO2 TiF6 2– HF Cl 2 TiCl 4 Ti2Cl 2 acac– The titanium ions in TiF6 2– and Ti2Cl 2 have a coordination number of 6. State what is meant by coordination number. Write an equation for the formation of TiF6 2– from TiO2. State what is meant by bidentate ligand. Ti2Cl 2 shows both optical and geometrical (cis/trans) isomerism. Ti2Cl 2 exists as three stereoisomers. The structure of one stereoisomer of Ti2Cl 2 is shown in Fig.3.2. acac acac Ti stereoisomer 1 Cl Cl Complete the structures of the other two stereoisomers of Ti2Cl 2. stereoisomer 2 Ti stereoisomer 3 Ti  The acac– anion is symmetrical. Deduce which, if any, of stereoisomers 1, 2 and 3 in are polar. Explain your answer. 
9701_m22_qp_42
THEORY
2022
Paper 4, Variant 2
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