11.3. Some reactions of the halide ions
A subsection of Chemistry, 9701, through 11. Group 17
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An aqueous solution of copper(sulfate is a blue colour due to the presence of [Cu(H2O)6]2+ complex ions. Write an equation for the reaction between [Cu(H2O)6]2+ ions and NaOH. Write an equation for the reaction between [Cu(H2O)6]2+ ions and an excess of conc.HCl. If an excess of ammonia is added to a solution of [Cu(H2O)6]2+ a deep blue solution containing [Cu(NH3)4(H2O)2]2+ complex ions is formed. There are two possible stereoisomers with the formula [Cu(NH3)4(H2O)2]2+. Complete the diagrams to show the two stereoisomers in the boxes below. isomer 1 isomer 2 Cu Cu  Use your answer in to deduce whether each of these isomers is polar or non-polar. polarity of isomer 1 polarity of isomer 2  The numerical value of the stability constant, Kstab, of the [Cu(NH3)4(H2O)2]2+ complex ion is 1.40×1013. Define stability constant. Compare the stabilities of the [Cu(H2O)6]2+ and [Cu(NH3)4(H2O)2]2+ complex ions. Explain your answer. Write an expression for the stability constant, Kstab, of the [Cu(NH3)4(H2O)2]2+ complex ion. State the units of the stability constant. Kstab =  units =  In a particular solution the concentration of the [Cu(NH3)4(H2O)2]2+ complex ion is 0.0074moldm–3 and the concentration of NH3 is 0.57 mol dm–3. Use your expression in and the Kstab value of 1.40×1013 to calculate the concentration of the [Cu(H2O)6]2+ complex ion in this solution.  concentration of [Cu(H2O)6]2+ = mol dm–3 Phenanthroline, C12H8N2, and ethanedioate ions, C2O4 2–, are bidentate ligands. Ruthenium(ions, Ru3+, form an octahedral complex with phenanthroline and chloride ions. The complex ion contains two phenanthroline molecules. Iron(ions, Fe3+, form an octahedral complex with ethanedioate ions only. Deduce the formula and charge of each of these complex ions. Ru3+ complex Fe3+ complex  
9701_w22_qp_41
THEORY
2022
Paper 4, Variant 1
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A transition element is a d-block element which forms one or more stable ions with incomplete d-orbitals. Two of the 3d orbitals are the 3dxy orbital and the 3dz2 orbital. Sketch the shapes of these two orbitals. 3dxy y z x 3dz2 z y x  The Ni2+ ion forms many different complexes. A solution containing the [Ni(H2O)6]2+ complex ion is green. When an excess of 1,2-diaminoethane, en, H2NCH2CH2NH2, is added, the colour of the solution changes to blue. This is due to the formation of the 2+ complex ion. Explain why the two solutions are coloured, and why the colours are different. The 2+ complex can exist as a mixture of two stereoisomers. Complete the three-dimensional diagram to show one of the stereoisomers. Each en ligand can be represented using N N . Ni  Name the geometry of the complex ion drawn in and the type of stereoisomerism shown by 2+. geometry stereoisomerism shown  Iron(carbonate, FeCO3, and nickel(carbonate, NiCO3, both decompose when heated. FeCO3 decomposes at a lower temperature than NiCO3. Suggest a possible reason for this difference. Explain your answer. A is a pale green salt containing Fe2+ ions. A sample of 2.62 g of A is dissolved in water and the solution is made up to exactly 100 cm3 with water. 25.0 cm3 samples of this solution are placed in conical flasks and titrated against 0.0100 mol dm–3 acidified potassiummanganate(. The equation for the only reaction that occurs is shown. 5Fe2+ + MnO4 – + 8H+ → 5Fe3+ + Mn2+ + 4H2O The average titre value is 35.0 cm3 of 0.0100 mol dm–3 acidified potassiummanganate(. Describe the colour change that is seen in the conical flask at the end-point of this titration. The colour changes from to �������������������������������������������� . Calculate the percentage by mass of iron in A. [Ar: Fe, 55.8]  percentage by mass of iron = % 
9701_w22_qp_43
THEORY
2022
Paper 4, Variant 3
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An aqueous solution of copper(sulfate is a blue colour due to the presence of [Cu(H2O)6]2+ complex ions. Write an equation for the reaction between [Cu(H2O)6]2+ ions and NaOH. Write an equation for the reaction between [Cu(H2O)6]2+ ions and an excess of conc.HCl. If an excess of ammonia is added to a solution of [Cu(H2O)6]2+ a deep blue solution containing [Cu(NH3)4(H2O)2]2+ complex ions is formed. There are two possible stereoisomers with the formula [Cu(NH3)4(H2O)2]2+. Complete the diagrams to show the two stereoisomers in the boxes below. isomer 1 isomer 2 Cu Cu  Use your answer in to deduce whether each of these isomers is polar or non-polar. polarity of isomer 1 polarity of isomer 2  The numerical value of the stability constant, Kstab, of the [Cu(NH3)4(H2O)2]2+ complex ion is 1.40×1013. Define stability constant. Compare the stabilities of the [Cu(H2O)6]2+ and [Cu(NH3)4(H2O)2]2+ complex ions. Explain your answer. Write an expression for the stability constant, Kstab, of the [Cu(NH3)4(H2O)2]2+ complex ion. State the units of the stability constant. Kstab =  units =  In a particular solution the concentration of the [Cu(NH3)4(H2O)2]2+ complex ion is 0.0074moldm–3 and the concentration of NH3 is 0.57 mol dm–3. Use your expression in and the Kstab value of 1.40×1013 to calculate the concentration of the [Cu(H2O)6]2+ complex ion in this solution.  concentration of [Cu(H2O)6]2+ = mol dm–3 Phenanthroline, C12H8N2, and ethanedioate ions, C2O4 2–, are bidentate ligands. Ruthenium(ions, Ru3+, form an octahedral complex with phenanthroline and chloride ions. The complex ion contains two phenanthroline molecules. Iron(ions, Fe3+, form an octahedral complex with ethanedioate ions only. Deduce the formula and charge of each of these complex ions. Ru3+ complex Fe3+ complex  
9701_w22_qp_43
THEORY
2022
Paper 4, Variant 3
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Transition elements behave as catalysts and can form complex ions. Explain why transition elements behave as catalysts. Silver forms the linear complex ion [Ag(CN)2]–. Copper forms the tetrahedral complex ion [Cu(CN)4]3−. Titanium forms the complex , where diars is a neutral bidentate ligand. State the oxidation state and the coordination number of titanium in . oxidation state coordination number Draw three-dimensional diagrams to show the shapes of [Ag(CN)2]– and [Cu(CN)4]3−, in the boxes. Label one bond angle on each diagram. Ag Cu The numerical value of the stability constant, Kstab, of the copper(complex [Cu(CN)4]3– is 2.0 × 1027. Write an expression for the Kstab of [Cu(CN)4]3−. Kstab = In a solution the concentrations of CN− and [Cu(CN)4]3− are both 0.0010 mol dm−3. Use your expression from and the value of Kstab to calculate the concentration of Cu+in this solution. concentration of Cu+= mol dm–3 A piece of a copper-containing alloy has a mass of 0.567 g. It is dissolved in an acid giving 100.0 cm3 of a blue solution in which all the copper is present as Cu2+ ions. An excess of KIis added to a 25.0 cm3 sample of this solution. All of the copper is precipitated as white CuI. Cu2+ ions are the only component in the solution that react with KI. This is reaction 1. reaction 1 2Cu2+ + 4I− 2CuI + I2 The liberated I2 is then titrated with 0.0200 mol dm–3 S2O3 2−. This is reaction 2. reaction 2 I2 + 2S2O3 2– 2I− + S4O6 2– The titration requires 20.10 cm3 of 0.0200 mol dm–3 S2O3 2– to reach the end-point. Calculate the number of moles of I2 that are reduced in this titration. number of moles of I2 = mol Calculate the number of moles of copper in the original piece of alloy. number of moles of copper = mol Calculate the percentage of copper in the alloy. percentage of copper = % Suggest why a solution of Cu2+ is coloured but solid CuI is white.
9701_w23_qp_41
THEORY
2023
Paper 4, Variant 1
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Five ligands are listed in Table 6.1. Table 6.1 ligand type of ligand NH3 EDTA4− CN− H2NCH2CH2NHCH2CH2NH2 tridentate C2O4 2− Complete Table 6.1 using the words monodentate, bidentate and polydentate only. Each of these three words may be used once, more than once, or not at all. The molecule H2NCH2CH2NHCH2CH2NH2 is a tridentate ligand. Suggest the meaning of tridentate ligand. Suggest how H2NCH2CH2NHCH2CH2NH2 acts as a tridentate ligand. Nickel forms the octahedral complex [Ni2(H2O)2]2+. This complex can exist in three isomeric forms, listed in Table 6.2. One of these forms is a trans isomer, the other forms are two different cis isomers. Table 6.2 isomer polarity trans isomer cis isomer 1 cis isomer 2 Complete Table 6.2 using the terms polar or non-polar. Each term may be used once, more than once, or not at all. Describe the difference between cis isomer 1 and cis isomer 2.
9701_w23_qp_41
THEORY
2023
Paper 4, Variant 1
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Transition elements behave as catalysts and can form complex ions. Explain why transition elements behave as catalysts. Silver forms the linear complex ion [Ag(CN)2]–. Copper forms the tetrahedral complex ion [Cu(CN)4]3−. Titanium forms the complex , where diars is a neutral bidentate ligand. State the oxidation state and the coordination number of titanium in . oxidation state coordination number Draw three-dimensional diagrams to show the shapes of [Ag(CN)2]– and [Cu(CN)4]3−, in the boxes. Label one bond angle on each diagram. Ag Cu The numerical value of the stability constant, Kstab, of the copper(complex [Cu(CN)4]3– is 2.0 × 1027. Write an expression for the Kstab of [Cu(CN)4]3−. Kstab = In a solution the concentrations of CN− and [Cu(CN)4]3− are both 0.0010 mol dm−3. Use your expression from and the value of Kstab to calculate the concentration of Cu+in this solution. concentration of Cu+= mol dm–3 A piece of a copper-containing alloy has a mass of 0.567 g. It is dissolved in an acid giving 100.0 cm3 of a blue solution in which all the copper is present as Cu2+ ions. An excess of KIis added to a 25.0 cm3 sample of this solution. All of the copper is precipitated as white CuI. Cu2+ ions are the only component in the solution that react with KI. This is reaction 1. reaction 1 2Cu2+ + 4I− 2CuI + I2 The liberated I2 is then titrated with 0.0200 mol dm–3 S2O3 2−. This is reaction 2. reaction 2 I2 + 2S2O3 2– 2I− + S4O6 2– The titration requires 20.10 cm3 of 0.0200 mol dm–3 S2O3 2– to reach the end-point. Calculate the number of moles of I2 that are reduced in this titration. number of moles of I2 = mol Calculate the number of moles of copper in the original piece of alloy. number of moles of copper = mol Calculate the percentage of copper in the alloy. percentage of copper = % Suggest why a solution of Cu2+ is coloured but solid CuI is white.
9701_w23_qp_43
THEORY
2023
Paper 4, Variant 3
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Five ligands are listed in Table 6.1. Table 6.1 ligand type of ligand NH3 EDTA4− CN− H2NCH2CH2NHCH2CH2NH2 tridentate C2O4 2− Complete Table 6.1 using the words monodentate, bidentate and polydentate only. Each of these three words may be used once, more than once, or not at all. The molecule H2NCH2CH2NHCH2CH2NH2 is a tridentate ligand. Suggest the meaning of tridentate ligand. Suggest how H2NCH2CH2NHCH2CH2NH2 acts as a tridentate ligand. Nickel forms the octahedral complex [Ni2(H2O)2]2+. This complex can exist in three isomeric forms, listed in Table 6.2. One of these forms is a trans isomer, the other forms are two different cis isomers. Table 6.2 isomer polarity trans isomer cis isomer 1 cis isomer 2 Complete Table 6.2 using the terms polar or non-polar. Each term may be used once, more than once, or not at all. Describe the difference between cis isomer 1 and cis isomer 2.
9701_w23_qp_43
THEORY
2023
Paper 4, Variant 3
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