2. Atoms, molecules and stoichiometry
A section of Chemistry, 9701
Listing 10 of 208 questions
Copper is a transition element and has atomic number 29. Complete the electronic configuration for the copper atom and the copper ion in the +2 oxidation state. • copper atom • copper ion in the +2 oxidation state The following equilibrium exists between two complex ions of copper in the +2 oxidation state. [Cu(H2O)6]2+ + 4Cl – [CuCl 4]2– + 6H2O Name the type of reaction occurring here. State the colours of these two complex ions. [Cu(H2O)6]2+ [CuCl 4]2– State the shape of the [CuCl 4]2– ion. Write the expression for the stability constant, Kstab, for this equilibrium. Kstab = Copper also forms the complex ions [Cu(NH3)2(H2O)4]2+ and [Cu(H2O)4]2+ where en is the bidentate ligand ethane-1,2-diamine, H2NCH2CH2NH2. [Cu(H2O)6]2+ + 2NH3 [Cu(NH3)2(H2O)4]2+ + 2H2O equilibrium 1 [Cu(H2O)6]2+ + en [Cu(H2O)4]2+ + 2H2O equilibrium 2 What is meant by the term bidentate ligand? The table lists the values of stability constants for these two complexes. stability constant, Kstab [Cu(NH3)2(H2O)4]2+ 7.94 × 107 [Cu(H2O)4]2+ 3.98 × 1010 What do these Kstab values tell us about the relative positions of equilibria 1 and 2? Nickel forms the complex ion 2+ in which it is surrounded octahedrally by six nitrogen atoms. Name the type of stereoisomerism displayed by 2+. Draw three-dimensional diagrams to show the two stereoisomers of 2+. Ethane-1,2-diamine is a useful reagent in organic chemistry. Explain how the amino groups in ethane-1,2-diamine allow the molecule to act as a Brønsted-Lowry base. Write an equation for the reaction of ethane-1,2-diamine with an excess of hydrochloricacid. Under certain conditions, ethane-1,2-diamine reacts with ethanedioic acid, HO2CCO2H, to form the polymer Z. Draw the structure of this polymer, Z, showing two repeat units. Name the type of reaction occurring during this polymerisation. Polymer Z is an example of a biodegradable polymer. Name a polymer that is non-biodegradable.
9701_w16_qp_41
THEORY
2016
Paper 4, Variant 1
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Cobalt is a transition element that forms complex ions with oxidation states +2 and +3. Explain what is meant by the term transition element. The following scheme shows some reactions of [Co(H2O)6]2+. precipitate A solution of C solution of B [Co(H2O)6]2+ OH–excess Cl –excess NH3State the formula of each of the following. A B C State the colour of the following solutions. [Co(H2O)6]2+ solution of B solution of C Define the term standard electrode potential. An electrochemical cell was set up to measure the standard electrode potential, , of a cell made of a Co2+ / Co half-cell and a Fe3+ / Fe2+ half-cell. Complete the table with the substance used to make the electrode in each of these half-cells. half-cell electrode Co2+ / Co Fe3+ / Fe2+ Write the equation for the overall cell reaction. Use the Data Booklet to calculate the . = V The electrochemical cell in was set up again but this time the concentration of Co2+was 0.050 mol dm–3. The Nernst equation can be used to calculate the value of an electrode potential at different concentrations. E = E o + (0.059 / z) log [Co2+] Nernst equation Use the Data Booklet and the Nernst equation to calculate the value of E for the Co2+ / Co half-cell in this experiment. E for Co2+ / Co = V Suggest how this change will affect the overall cell potential, Ecell, compared to in . Circle your answer. less positive no change more positive Iron(ions can oxidise vanadium metal. Construct an equation for the reaction of an excess of iron(ions with vanadium metal. Use of the Data Booklet will be helpful.
9701_w16_qp_41
THEORY
2016
Paper 4, Variant 1
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Copper is a transition element and has atomic number 29. Complete the electronic configuration for the copper atom and the copper ion in the +2 oxidation state. • copper atom • copper ion in the +2 oxidation state The following equilibrium exists between two complex ions of copper in the +2 oxidation state. [Cu(H2O)6]2+ + 4Cl – [CuCl 4]2– + 6H2O Name the type of reaction occurring here. State the colours of these two complex ions. [Cu(H2O)6]2+ [CuCl 4]2– State the shape of the [CuCl 4]2– ion. Write the expression for the stability constant, Kstab, for this equilibrium. Kstab = Copper also forms the complex ions [Cu(NH3)2(H2O)4]2+ and [Cu(H2O)4]2+ where en is the bidentate ligand ethane-1,2-diamine, H2NCH2CH2NH2. [Cu(H2O)6]2+ + 2NH3 [Cu(NH3)2(H2O)4]2+ + 2H2O equilibrium 1 [Cu(H2O)6]2+ + en [Cu(H2O)4]2+ + 2H2O equilibrium 2 What is meant by the term bidentate ligand? The table lists the values of stability constants for these two complexes. stability constant, Kstab [Cu(NH3)2(H2O)4]2+ 7.94 × 107 [Cu(H2O)4]2+ 3.98 × 1010 What do these Kstab values tell us about the relative positions of equilibria 1 and 2? Nickel forms the complex ion 2+ in which it is surrounded octahedrally by six nitrogen atoms. Name the type of stereoisomerism displayed by 2+. Draw three-dimensional diagrams to show the two stereoisomers of 2+. Ethane-1,2-diamine is a useful reagent in organic chemistry. Explain how the amino groups in ethane-1,2-diamine allow the molecule to act as a Brønsted-Lowry base. Write an equation for the reaction of ethane-1,2-diamine with an excess of hydrochloricacid. Under certain conditions, ethane-1,2-diamine reacts with ethanedioic acid, HO2CCO2H, to form the polymer Z. Draw the structure of this polymer, Z, showing two repeat units. Name the type of reaction occurring during this polymerisation. Polymer Z is an example of a biodegradable polymer. Name a polymer that is non-biodegradable.
9701_w16_qp_43
THEORY
2016
Paper 4, Variant 3
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Cobalt is a transition element that forms complex ions with oxidation states +2 and +3. Explain what is meant by the term transition element. The following scheme shows some reactions of [Co(H2O)6]2+. precipitate A solution of C solution of B [Co(H2O)6]2+ OH–excess Cl –excess NH3State the formula of each of the following. A B C State the colour of the following solutions. [Co(H2O)6]2+ solution of B solution of C Define the term standard electrode potential. An electrochemical cell was set up to measure the standard electrode potential, , of a cell made of a Co2+ / Co half-cell and a Fe3+ / Fe2+ half-cell. Complete the table with the substance used to make the electrode in each of these half-cells. half-cell electrode Co2+ / Co Fe3+ / Fe2+ Write the equation for the overall cell reaction. Use the Data Booklet to calculate the . = V The electrochemical cell in was set up again but this time the concentration of Co2+was 0.050 mol dm–3. The Nernst equation can be used to calculate the value of an electrode potential at different concentrations. E = E o + (0.059 / z) log [Co2+] Nernst equation Use the Data Booklet and the Nernst equation to calculate the value of E for the Co2+ / Co half-cell in this experiment. E for Co2+ / Co = V Suggest how this change will affect the overall cell potential, Ecell, compared to in . Circle your answer. less positive no change more positive Iron(ions can oxidise vanadium metal. Construct an equation for the reaction of an excess of iron(ions with vanadium metal. Use of the Data Booklet will be helpful.
9701_w16_qp_43
THEORY
2016
Paper 4, Variant 3
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Complete the following electronic structures. ● the iron atom, Fe 1s22s22p6 ● the iron(ion, Fe3+ 1s22s22p6 Solutions of iron(salts are acidic due to the equilibrium shown. [Fe(H2O)6]3+[Fe(H2O)5(OH)]2++ H+ Ka = 8.9 × 10–4 mol dm–3 Calculate the pH of a 0.25 mol dm–3 FeCl 3 solution. pH = The table shows numerical values of the stability constants for the following equilibrium where M can be one of the metal ions listed and L one of the ligands which replaces one H2O molecule. [M(H2O)6]n++ L–[M(H2O)5L](n–1)++ H2Ometal ion, M ligand, L stability constant, Kstab Fe3+ F– 1.0 × 106 Fe3+ Cl – 2.5 × 101 Fe3+ SCN– 9.0 × 102 Hg2+ Cl – 5.0 × 106 What is meant by the term stability constant, Kstab? Use the data in the table to predict the formula of the complex formed in the greatest amount when ● a solution containing equal concentrations of both F– and SCN– ions is added to Fe3+, ● a solution containing equal concentrations of both Fe3+ and Hg2+ ions is added to Cl –. Ethanedioate ions, –O2CCO2 –, are bidentate ligands. The abbreviation ed 2– can be used to represent ethanedioate ions. The complex [Fe(ed )2Cl 2]3– can be formed according to the equation shown. [Fe(H2O)4Cl 2]++ 2ed 2–[Fe(ed )2Cl 2]3–+ 4H2OWrite the expression for the equilibrium constant, Kstab, and state its units. Kstab = units [Fe(ed )2Cl 2]3– shows geometrical and optical isomerism. Complete the three-dimensional diagrams to show the three stereoisomers of [Fe(ed )2Cl 2]3–. You may use –O O– to represent ed 2–. Fe isomer A Fe isomer B Fe isomer C Give the letters of two isomers of [Fe(ed )2Cl 2]3– which are geometrical isomers of each other. Give the letters of the two isomers of [Fe(ed )2Cl 2]3– which show optical isomerism. Give the letter of the isomer which has no dipole moment.
9701_w17_qp_41
THEORY
2017
Paper 4, Variant 1
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An electrochemical cell consists of a half-cell containing V3+and V2+ions and another half‑cell containing VO2 +and VO2+ions. Use data from the Data Booklet to calculate a value for the . = V Write the ionic equation for the cell reaction. Draw a fully labelled diagram of the apparatus you could use to measure the potential of this cell. Include the necessary chemicals. Use data from the Data Booklet to predict whether a reaction might take place when the following pairs of aqueous solutions are mixed. If a reaction occurs, write an equation for it and calculate the . ● V2+and Sn4+Does a reaction occur? equation ● VO2+and Fe3+Does a reaction occur? equation
9701_w17_qp_42
THEORY
2017
Paper 4, Variant 2
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Complete the following electronic structures. ● the iron atom, Fe 1s22s22p6 ● the iron(ion, Fe3+ 1s22s22p6 Solutions of iron(salts are acidic due to the equilibrium shown. [Fe(H2O)6]3+[Fe(H2O)5(OH)]2++ H+ Ka = 8.9 × 10–4 mol dm–3 Calculate the pH of a 0.25 mol dm–3 FeCl 3 solution. pH = The table shows numerical values of the stability constants for the following equilibrium where M can be one of the metal ions listed and L one of the ligands which replaces one H2O molecule. [M(H2O)6]n++ L–[M(H2O)5L](n–1)++ H2Ometal ion, M ligand, L stability constant, Kstab Fe3+ F– 1.0 × 106 Fe3+ Cl – 2.5 × 101 Fe3+ SCN– 9.0 × 102 Hg2+ Cl – 5.0 × 106 What is meant by the term stability constant, Kstab? Use the data in the table to predict the formula of the complex formed in the greatest amount when ● a solution containing equal concentrations of both F– and SCN– ions is added to Fe3+, ● a solution containing equal concentrations of both Fe3+ and Hg2+ ions is added to Cl –. Ethanedioate ions, –O2CCO2 –, are bidentate ligands. The abbreviation ed 2– can be used to represent ethanedioate ions. The complex [Fe(ed )2Cl 2]3– can be formed according to the equation shown. [Fe(H2O)4Cl 2]++ 2ed 2–[Fe(ed )2Cl 2]3–+ 4H2OWrite the expression for the equilibrium constant, Kstab, and state its units. Kstab = units [Fe(ed )2Cl 2]3– shows geometrical and optical isomerism. Complete the three-dimensional diagrams to show the three stereoisomers of [Fe(ed )2Cl 2]3–. You may use –O O– to represent ed 2–. Fe isomer A Fe isomer B Fe isomer C Give the letters of two isomers of [Fe(ed )2Cl 2]3– which are geometrical isomers of each other. Give the letters of the two isomers of [Fe(ed )2Cl 2]3– which show optical isomerism. Give the letter of the isomer which has no dipole moment.
9701_w17_qp_43
THEORY
2017
Paper 4, Variant 3
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Ethanedioate ions, C2O4 2–, are bidentate ligands. Explain what is meant by the term ligand. Cr3+and C2O4 2–ions form the complex ion [Cr(C2O4)2(H2O)2]–. Draw two stereoisomers of this complex ion. You may use O O to represent C2O4 2–. Cr Cr  The solubility of calcium ethanedioate, CaC2O4, is 6.65×10–3 g dm–3 at 298 K. Write an expression for the solubility product, Ksp, of CaC2O4. Include its units. Ksp =  units =  Calculate the numerical value of Ksp CaC2O4 at 298 K. Give your answer in standard form to two significant figures.  Ksp CaC2O4 = 
9701_w18_qp_41
THEORY
2018
Paper 4, Variant 1
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Questions Discovered
208