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11.3. Some reactions of the halide ions
A subsection of Chemistry, 9701, through 11. Group 17
Listing 10 of 171 questions
An aqueous solution of chromium(contains the green [Cr(H2O)6]3+ complex ion. Complete the electronic configuration of an isolated, gaseous Cr3+ ion. 1s2 ��������������������������������������������������������������������������������������������������������������������������������� Define the term complex ion. [Cr(H2O)6]3+shows some similar chemical properties to [Co(H2O)6]2+. Samples of [Cr(H2O)6]3+ are reacted separately with either NaOH, H2O2, or excess NH3. Use this information and the Data Booklet to suggest the formula of the chromium species formed. State the type of reaction taking place in each case. reagent added to [Cr(H2O)6]3+formula of chromium species formed type of reaction NaOHH2O2an excess of NH3 [Cr(H2O)6]2+ and [Cr2(O2CCH3)4(H2O)2] are both complexes of chromium(and have different colours. Explain why the colours of these complexes are different. The structure of [Cr2(O2CCH3)4(H2O)2] is shown. Ethanoate ions act as ligands in this complex. The ethanoate ligand, CH3CO2 –, is shown as O O. Cr O O O H2O O O O O OH2 O Cr Water and ethanoate ions behave as different types of ligand in this complex. Suggest an explanation for this statement. Deduce the coordination number of Cr and the geometry around each Cr atom in this structure. coordination number geometry around Cr atom ���������������������������������������������������������������������������������������������������  State the type of bond between the two atoms in the Cr–Cr bond. The [Cr2(O2CCH3)4(H2O)2] complex reacts with aqueous acid to form Cr2+ions. Cr2+ions react with O2under acidic conditions. Cr3+ions are formed. Use the Data Booklet to answer the following questions. Construct an ionic equation for the reaction of Cr2+with O2under acidic conditions. Calculate for the reaction in .  = V 
9701_s21_qp_42
THEORY
2021
Paper 4, Variant 2
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Define the term standard electrode potential. Three redox systems, A, B and C, are shown. The ligand 1,2-diaminoethane, H2NCH2CH2NH2, is represented by en. A [Ru(H2O)6]3+ + e– [Ru(H2O)6]2+ B [Ru(NH3)6]3+ + e– [Ru(NH3)6]2+ C 3+ + e– 2+ Two electrochemical cells are set up to compare the standard electrode potentials, E o, of three half-cells. The diagrams show the relative potential of each electrode. [Ru(NH3)6]3+ [Ru(NH3)6]2+ salt bridge V 3+ 2+ + – Pt Pt [Ru(H2O)6]3+ [Ru(H2O)6]2+ salt bridge V 3+ 2+ + – Pt Pt Use this information to complete the table by adding the labels A, B and C to deduce the order of E o for the three half-cells. E o redox system most negative least negative  The complex 3+ shows stereoisomerism. The ligand en is bidentate. Draw three-dimensional diagrams to show the two isomers of 3+. Represent the ligand en by using N N . Name the type of stereoisomerism. isomer 1 Ru isomer 2 Ru type of stereoisomerism  An electrochemical cell consists of a Br2/Br – half-cell and a Ag+/Ag half-cell, under standard conditions. Use the Data Booklet to calculate the . Deduce the direction of electron flow in the wire through the voltmeter between these two half-cells. = V direction of electron flow from to ����������������������������������������� Water is added to the Ag+/Ag half-cell in . Suggest the effect of this addition on the Ecell. Place a tick ( ) in the appropriate box. less positive no change more positive Explain your answer. Silver bromide, AgBr, dissolves in an aqueous solution of S2O3 2– ions to form the complex ion [Ag(S2O3)2]3–. The S2O3 2– ions act as monodentate ligands. equilibrium 1 AgBr+ 2S2O3 2–[Ag(S2O3)2]3–+ Br –Define the term ligand. Write an expression for the equilibrium constant, Kc, for equilibrium1. Kc =  Some additional data are given about the dissolution of AgBr in S2O3 2–. equilibrium constant numerical value solubility product, Ksp, of AgBr 5.4 × 10–13 stability constant, Kstab, of [Ag(S2O3)2]3– 2.9 × 1013 Use your answer to and these data to calculate Kc for equilibrium1. Include the units for Kc.  Kc = units The numerical values for the stability constants, Kstab, of two other silver(complexes are given. silver(complex numerical value of Kstab [Ag(CN)2]– 5.3 × 1018 [Ag(NH3)2]+ 1.6 × 107 An aqueous solution containing Ag+ is added to a solution containing equal concentrations of CN–, NH3and S2O3 2–. The mixture is left to reach equilibrium. Deduce the relative concentrations of [Ag(CN)2]–, [Ag(NH3)2]+ and [Ag(S2O3)2]3– present in the resulting mixture. Explain your answer. > > highest concentration lowest concentration 
9701_s21_qp_42
THEORY
2021
Paper 4, Variant 2
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Explain why chromium complexes are coloured. Four different compounds can be obtained when anhydrous chromium(chloride reacts with water under various conditions. When samples of each compound are reacted separately with aqueous silvernitrate, different amounts of silverchloride are precipitated. The precipitation leaves the complex ions P, Q, R and S in solution. formula of compound moles of AgCl precipitated per mole of complex ion complex ion property of complex ion CrCl 3(H2O)6 P non-polar CrCl 3(H2O)5 Q polar CrCl 3(H2O)4 R polar CrCl 3(H2O)4 S non-polar Draw three-dimensional diagrams for the structures of complex ions P, Q, R and S. Include the charges for each complex ion. P Cr Q Cr R Cr S Cr  Suggest why complex ion S is non-polar. The structure of picolinicacid is shown. picolinic acid CO2H N The conjugate base of picolinicacid is a bidentate ligand, Z. Define the term bidentate ligand. Draw the structure of Z.  Z reacts with aqueous chromium(ions, [Cr(H2O)6]3+, in a 3 : 1 ratio to form a new neutral complex. State the coordination number and the geometry of the chromium(centre in the complex. coordination number geometry ����������������������������������������� (NH4)2Cr2O7 decomposes readily on heating to form Cr2O3, steam and an inert colourless gas. Deduce the oxidation numbers of chromium in (NH4)2Cr2O7 and in Cr2O3. (NH4)2Cr2O7 Cr2O3 ��������������������������������������������������� Construct an equation for the thermal decomposition of (NH4)2Cr2O7. 
9701_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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Define the term transition element. State how the melting point and density of iron compare to those of calcium. Define the term standard cell potential, . Draw a fully labelled diagram of the apparatus that can be used to measure the cell potential of a cell composed of a Cu(/Cu electrode and an Fe(/Fe(electrode. Include all necessary reactants.  The reaction between S2O8 2–and I –is catalysed by adding a few drops of Fe3+. Use equations to show the catalytic role of Fe3+ in this reaction.  Fe3+can oxidise I –, whereas [Fe(CN)6]3–cannot oxidise I –. Use E o values to explain these observations. When aqueous solutions of S2O8 2– and tartrate ions are mixed the reaction proceeds very slowly. However, this reaction proceeds quickly in the presence of an Fe3+catalyst. The overall equation for this reaction is shown. tartrate ions + 3S2O8 2– + 2H2O 2CO2 + 2HCO2 – + 6H+ + 6SO4 2– OH OH CO2 – –O2C Suggest why this reaction is slow without the Fe3+ catalyst. Use the overall equation to deduce the half-equation for the oxidation of tartrate ions, C4H4O6 2–, to carbondioxide, CO2, and methanoate ions, HCO2 –. C4H4O6 2– +  Complete the following table to show the structures of the organic products formed when tartaric acid reacts separately with each reagent. Identify each type of reaction. tartaric acid OH OH CO2H HO2C reagent structure of organic product type of reaction an excess of LiAl H4 an excess of CH3COCl  Tartaric acid reacts with the amine 1-phenylethylamine, C6H5CH(NH2)CH3, to form an ionicsalt. Draw the structure of the salt formed in this reaction. Include the charges on the ions.  
9701_s21_qp_43
THEORY
2021
Paper 4, Variant 3
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State the relative basicities of ethanamide, diethylamine and ethylamine in aqueous solution. Explain your answer. > > most basic least basic The amino acid alanine, H2NCH(CH3)COOH, can act as a buffer. Define a buffer solution. Write two equations to show how an aqueous solution of alanine can act as a buffer solution. Glutamic acid is another amino acid that acts as a buffer. glutamic acid C H2N COOH H CH2CH2COOH Draw the skeletal formula for glutamic acid. Draw the structure for the dipeptide, ala‑glu, formed from one molecule of alanine and one molecule of glutamic acid. The peptide bond formed should be displayed. The isoelectric point of alanine is 6.0 and of glutamic acid is 3.2. A mixture of the dipeptide, ala‑glu, and its two constituent amino acids, alanine and glutamic acid, is analysed by electrophoresis using a buffer at pH 6.0. + – mixture applied here Draw and label three spots on to indicate the predicted position of each of these three species after electrophoresis. Explain your answer. Alanine, H2NCH(CH3)COOH, reacts with methanol to form the ester G under certain conditions. The proton (1H) NMR spectrum of G dissolved in D2O is shown in . G O O chemical shift δ / ppm H2N Table 7.1 environment of proton example chemical shift range, δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 attached to aromatic ring H–Ar 6.0–9.0 aldehyde HCOR 9.3–10.5 alcohol ROH 0.5–6.0 phenol Ar–OH 4.5–7.0 carboxylic acid RCOOH 9.0–13.0 alkyl amine R–NH– 1.0–5.0 aryl amine Ar–NH2 3.0–6.0 amide RCONHR 5.0–12.0 Complete Table 7.2 for the proton (1H) NMR spectrum of G. Table 7.2 chemical shift (δ) splitting pattern number of 1H atoms responsible for the peak number of protons on adjacent carbon atoms 1.4 3.5 4.0 The proton (1H) NMR spectrum of G dissolved in CDCl3 is obtained. Describe the difference observed between this spectrum and the proton NMR spectrum in D2O shown in Fig 7.3. Explain your answer.
9701_s23_qp_41
THEORY
2023
Paper 4, Variant 1
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State the relative basicities of ethanamide, diethylamine and ethylamine in aqueous solution. Explain your answer. > > most basic least basic The amino acid alanine, H2NCH(CH3)COOH, can act as a buffer. Define a buffer solution. Write two equations to show how an aqueous solution of alanine can act as a buffer solution. Glutamic acid is another amino acid that acts as a buffer. glutamic acid C H2N COOH H CH2CH2COOH Draw the skeletal formula for glutamic acid. Draw the structure for the dipeptide, ala‑glu, formed from one molecule of alanine and one molecule of glutamic acid. The peptide bond formed should be displayed. The isoelectric point of alanine is 6.0 and of glutamic acid is 3.2. A mixture of the dipeptide, ala‑glu, and its two constituent amino acids, alanine and glutamic acid, is analysed by electrophoresis using a buffer at pH 6.0. + – mixture applied here Draw and label three spots on to indicate the predicted position of each of these three species after electrophoresis. Explain your answer. Alanine, H2NCH(CH3)COOH, reacts with methanol to form the ester G under certain conditions. The proton (1H) NMR spectrum of G dissolved in D2O is shown in . G O O chemical shift δ / ppm H2N Table 7.1 environment of proton example chemical shift range, δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 attached to aromatic ring H–Ar 6.0–9.0 aldehyde HCOR 9.3–10.5 alcohol ROH 0.5–6.0 phenol Ar–OH 4.5–7.0 carboxylic acid RCOOH 9.0–13.0 alkyl amine R–NH– 1.0–5.0 aryl amine Ar–NH2 3.0–6.0 amide RCONHR 5.0–12.0 Complete Table 7.2 for the proton (1H) NMR spectrum of G. Table 7.2 chemical shift (δ) splitting pattern number of 1H atoms responsible for the peak number of protons on adjacent carbon atoms 1.4 3.5 4.0 The proton (1H) NMR spectrum of G dissolved in CDCl3 is obtained. Describe the difference observed between this spectrum and the proton NMR spectrum in D2O shown in Fig 7.3. Explain your answer.
9701_s23_qp_43
THEORY
2023
Paper 4, Variant 3
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Define transition element. Explain why transition elements can form complex ions. The 3d orbitals in an isolated Ag+ ion are degenerate. Define degenerate d orbitals. Sketch the shape of a 3dxy orbital in . z y x Tollens’ reagent can be used to distinguish between aldehydes and ketones. Tollens’ reagent contains [Ag(NH3)2]OH, which can be prepared in a two-step process. step 1 Aqueous NaOH is added dropwise to aqueous AgNO3 to form Ag2O as a brown precipitate. step 2 Aqueous NH3 is added dropwise to Ag2O to form a colourless solution containing [Ag(NH3)2]OH. Construct equations for each of the steps in the preparation of [Ag(NH3)2]OH. step 1 step 2 Name the shape of the complex ion [Ag(NH3)2]+. State the bond angle for H-N-Ag and for N-Ag-N. shape bond angle for H-N-Ag = ° bond angle for N-Ag-N = ° An electrochemical cell uses Ag2O as the positive electrode and Zn as the negative electrode immersed in an alkaline electrolyte. The overall cell reaction is shown. Ag2O + Zn + H2O 2Ag + Zn(OH)2 Complete the half-equation for the reaction at each electrode. at the positive electrode Ag2O + at the negative electrode Zn + Coordination polymers are made when a bidentate ligand acts as a bridge between different metal ions. Under certain conditions Ru3+and the bidentate ligand dps can form a coordination polymer containing ([RuCl 4]–)n chains. N N S dps The bidentate ligand dps uses each of the nitrogen atoms to bond to a different Ru3+. Complete by drawing the structure for the coordination polymer ([RuCl 4]–)n. Show two repeat units. The dps ligand can be represented using N N . Ru
9701_s24_qp_41
THEORY
2024
Paper 4, Variant 1
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Explain why transition elements have variable oxidation states. Sketch the shape of a 3dz2 orbital in . z y x Samples of [Cu(H2O)6]2+are reacted separately with an excess of solution A and with an excess of solution B. The reaction of [Cu(H2O)6]2+with solution A is a precipitation reaction. The reaction of [Cu(H2O)6]2+with solution B is a ligand substitution reaction. Suggest a possible identity for solution A and for solution B. Give relevant observations and the formula of the copper‑containing product for each reaction. solution A observations formula of the copper‑containing product solution B observations formula of the copper‑containing product Solutions containing the [Ag(NH3)2]+ complex are colourless. Explain why this complex is colourless. Two bidentate ligands are shown in . en dpys S N N NH2 H2N Explain what is meant by a bidentate ligand. ,   , Ruthenium(ions, Ru3+, form an octahedral complex, +, with the ligands dpys and chloride ions. This complex shows the same kind of stereoisomerism as [Ru(NH3)4Cl2]+ but also shows a different type of stereoisomerism. Complete the three‑dimensional diagrams in to show the three different stereoisomers of +. The dpys ligand can be represented using N N. isomer 1 Ru isomer 2 Ru isomer 3 Ru State the different types of stereoisomerism shown by +. Deduce which stereoisomers in are non-polar. Explain your answer. ,   ,
9701_s24_qp_42
THEORY
2024
Paper 4, Variant 2
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