11.2. The chemical properties of the halogen elements and the hydrogen halides
A subsection of Chemistry, 9701, through 11. Group 17
Listing 10 of 102 questions
Use The elements of Group IV all form tetrachlorides with the general formula M Cl 4. Draw a diagram of a molecule of SiCl 4 stating bond angles. Describe and explain how the volatilities of the Group IV chlorides vary down the group. The relative stabilities of the M 2+and M 4+ions also vary down Group IV. Use the Data Booklet to illustrate this observation when M = Sn and M = Pb. Use the Data Booklet to predict the products formed, and write equations for the reactions occurring, when • an equimolar mixture of Sn2+and Sn4+is added to I2, • an equimolar mixture of Pb2+and Pb4+is added to SO2. Examiner’s Use The Sn–Cl bond energy is +315 kJ mol–1. Use this and other values from the Data Booklet to calculate DH o for the reaction M Cl 2+ Cl 2M Cl 4for the following cases. • M = Si DH o = kJ mol–1 • M = Sn DH o = kJ mol–1 Do your results agree with the trend in relative stabilities of the +2 and +4 oxidation states in ? Explain your answer.
9701_s08_qp_4
THEORY
2008
Paper 4, Variant 0
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Fluorine is much more electronegative than both silicon and sulfur, but whereas the molecule of SF4 has an overall dipole, that of SiF4 has none. Suggest a reason for this difference. Predict whether or not the following molecules will have an overall dipole. Place a tick in the appropriate column. compound molecule has an overall dipole molecule does not have an overall dipole BCl 3 PCl 3 CCl 4 SF6 Boron and silicon are two elements adjacent to carbon in the periodic table. CCl4 does not react with water, whereas BCl 3 and SiCl4 do react. Suggest a reason for this difference in reactivity. Construct equations showing the reaction of these two chlorides with an excess of water. BCl 3 SiCl4 When reacted with a small quantity of water, SiCl 4 produces an oxychloride X, SixCl yOz. The mass spectrum of X shows peaks at mass numbers of 133, 149, 247, 263 and 396. (You should assume that the species responsible for all these peaks contain the 16O, the 35Cl and the 28Si isotopes only.) Use these data to deduce the molecular formula of X. molecular formula Suggest the structures of the fragments responsible for the peaks at the following mass numbers. mass number structure Hence suggest the displayed formula of X.
9701_s10_qp_42
THEORY
2010
Paper 4, Variant 2
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The design and development of batteries has been a major research area in recent years. Lead-acid batteries, used in cars, are made up of a number of rechargeable cells in series, and were first developed in 1860. They have the disadvantage of a relatively high mass compared to the energy stored. During discharge, the electrode reactions in the cells of these batteries are as follows. I Pb + SO4 2– J PbSO4 + 2e– II PbO2 + 4H+ + SO4 2– + 2e– J PbSO4 + 2H2O State which of these reactions occurs at the positive electrode in a lead-acid cell during discharge, explaining your answer. Use the Data Booklet and the equations I and II above to calculate the voltage produced by a lead-acid cell under standard conditions. Nickel-metal hydride batteries were developed in the 1980s and have become increasingly common particularly for small devices such as mobile phones and digital cameras that need near-constant sources of electrical energy. These cells use nickel oxohydroxide (NiO(OH)) as one electrode and a hydrogen-absorbing alloy such as LiNi5 as the other electrode. One reaction that takes place in these batteries is NiO(OH) + H2O + e– Ni(OH)2 + OH– State the oxidation state of nickel in NiO(OH). Suggest a likely advantage of these batteries compared with lead-acid batteries. Hydrogen fuel cells have been suggested as the next major advance in electrically powered vehicles. In these fuel cells hydrogen is oxidized to produce water, using a catalyst and inert electrodes. Suggest a material for the electrodes. Use your knowledge of hydrogen to suggest a disadvantage of these fuel cells in powering vehicles. Many of the world’s countries are developing ways of recycling materials which are valuable or which require large amounts of energy to produce. For each of the following recyclable materials, state whether recycling of this material is important in saving energy or in saving resources. Use your knowledge of chemistry to explain each choice. glass steel plastics
9701_s10_qp_42
THEORY
2010
Paper 4, Variant 2
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Fluorine is much more electronegative than both silicon and sulfur, but whereas the molecule of SF4 has an overall dipole, that of SiF4 has none. Suggest a reason for this difference. Predict whether or not the following molecules will have an overall dipole. Place a tick in the appropriate column. compound molecule has an overall dipole molecule does not have an overall dipole BCl 3 PCl 3 CCl 4 SF6 Boron and silicon are two elements adjacent to carbon in the periodic table. CCl4 does not react with water, whereas BCl 3 and SiCl4 do react. Suggest a reason for this difference in reactivity. Construct equations showing the reaction of these two chlorides with an excess of water. BCl 3 SiCl4 When reacted with a small quantity of water, SiCl 4 produces an oxychloride X, SixCl yOz. The mass spectrum of X shows peaks at mass numbers of 133, 149, 247, 263 and 396. (You should assume that the species responsible for all these peaks contain the 16O, the 35Cl and the 28Si isotopes only.) Use these data to deduce the molecular formula of X. molecular formula Suggest the structures of the fragments responsible for the peaks at the following mass numbers. mass number structure Hence suggest the displayed formula of X.
9701_s10_qp_43
THEORY
2010
Paper 4, Variant 3
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The design and development of batteries has been a major research area in recent years. Lead-acid batteries, used in cars, are made up of a number of rechargeable cells in series, and were first developed in 1860. They have the disadvantage of a relatively high mass compared to the energy stored. During discharge, the electrode reactions in the cells of these batteries are as follows. I Pb + SO4 2– J PbSO4 + 2e– II PbO2 + 4H+ + SO4 2– + 2e– J PbSO4 + 2H2O State which of these reactions occurs at the positive electrode in a lead-acid cell during discharge, explaining your answer. Use the Data Booklet and the equations I and II above to calculate the voltage produced by a lead-acid cell under standard conditions. Nickel-metal hydride batteries were developed in the 1980s and have become increasingly common particularly for small devices such as mobile phones and digital cameras that need near-constant sources of electrical energy. These cells use nickel oxohydroxide (NiO(OH)) as one electrode and a hydrogen-absorbing alloy such as LiNi5 as the other electrode. One reaction that takes place in these batteries is NiO(OH) + H2O + e– Ni(OH)2 + OH– State the oxidation state of nickel in NiO(OH). Suggest a likely advantage of these batteries compared with lead-acid batteries. Hydrogen fuel cells have been suggested as the next major advance in electrically powered vehicles. In these fuel cells hydrogen is oxidized to produce water, using a catalyst and inert electrodes. Suggest a material for the electrodes. Use your knowledge of hydrogen to suggest a disadvantage of these fuel cells in powering vehicles. Many of the world’s countries are developing ways of recycling materials which are valuable or which require large amounts of energy to produce. For each of the following recyclable materials, state whether recycling of this material is important in saving energy or in saving resources. Use your knowledge of chemistry to explain each choice. glass steel plastics
9701_s10_qp_43
THEORY
2010
Paper 4, Variant 3
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