9701_s16_qp_42
A paper of Chemistry, 9701
Questions:
10
Year:
2016
Paper:
4
Variant:
2
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1
Magnesium nitrate, Mg(NO3)2, is very soluble in water. When a hot saturated solution of magnesium nitrate is cooled, crystals of the hydrate, Mg(NO3)2.6H2O, are formed. In the crystals, six water molecules bond to each Mg2+ ion, and some of these water molecules are also bonded to the nitrate ions. Suggest the type of bonding that occurs between H2O and Mg2+, H2O and NO3 –. Describe the arrangement of the water molecules around the Mg2+ ion. Describe in detail what you would observe when crystals of Mg(NO3)2.6H2O are heated in a boiling tube, gently at first and then more strongly. Write equations for any reactions that occur. Calculate the percentage loss in mass when Mg(NO3)2.6H2O is heated strongly to constant mass. percentage loss = % Explain why the Group 2 nitrates become more stable to heat down the group. Magnesium nitrate and silver nitrate, AgNO3, decompose on heating to produce the same gases. Silver nitrate also produces silver metal during decomposition. Write an equation for the decomposition of AgNO3.
10. Group 2  →  10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
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Ethanoic acid is a weak acid. Explain what is meant by the term weak acid. The pKa values of four acids are listed below. acid structural formula pKa CH3CO2H 4.8 CH3CH2CO2H 4.9 CH3CHCl CO2H 2.8 CH2Cl CH2CO2H 4.0 State the mathematical relationship between pKa and the acid dissociation constant Ka. With reference to acidity, explain the difference in pKa values between • acid 1 and acid 2, • acid 2 and acid 3, • acid 3 and acid 4. Draw a fully labelled diagram of the equipment needed to measure the voltage of an electrochemical cell consisting of the standard hydrogen electrode and the standard Cu / Cu2+ electrode. For the cell drawn in , calculate the and state which electrode is positive. = identity of the positive electrode A monobasic acid, D, has Ka = 1.23 × 10–5 mol dm–3. Calculate the pH of a 0.100 mol dm–3 solution of D. pH = An electrochemical cell similar to the one you have drawn in was set up using a 0.100 mol dm–3 solution of D in the hydrogen electrode instead of the standard solution. Use the data and the Nernst equation, E = E o + 0.059 log [H+], to calculate the new E cell in this experiment. E cell = V
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
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2-bromopropane can be used to synthesise methylethylamine and 2-methylpropylamine. Br 2-bromopropane 2-methylpropylamine NH2 methylethylamine reaction 1 reaction 2 reaction 3 X NH2 Draw the structure of the intermediate X in the box above. Suggest reagents and conditions for • reaction 1, • reaction 2, • reaction 3. Write an equation showing why aqueous solutions of ethylamine are alkaline. Compare the basicities of ethylamine and ammonia. Explain your answer. Solutions containing mixtures of amines and their salts are buffer solutions. Explain what is meant by the term buffer solution. Write two equations to show how a solution containing a mixture of CH3NH2 and CH3NH3Cl acts as a buffer.
15. Halogen compounds  →  15.1. Halogenoalkanes
14. Hydrocarbons  →  14.2. Alkenes
19. Nitrogen compounds  →  19.1. Primary amines
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There are two isomeric complexes with the formula Pt(NH3)2Cl 2, one of which is an anti-cancer drug. Draw diagrams to show the three-dimensional structures of the two isomers. isomer 1 isomer 2 Comment on the polarity of the two isomers of Pt(NH3)2Cl 2. Explain your answer. Oxaloplatin is another successful anti-cancer drug in which the stereochemistry around the platinum atom is the same as that in Pt(NH3)2Cl 2. Pt NH2 NH2 O O O O C C oxaloplatin Explain why there are no isomers of oxaloplatin. Only one structure of the complex [Ni(R3P)2Cl 2] is known. (R=CH3,R3Pisamonodentateligand) What does this indicate about the stereochemistry around the nickel atom? Draw a three-dimensional diagram showing the structure of this complex.
13. An introduction to AS Level organic chemistry  →  13.4. Isomerism: structural isomerism and stereoisomerism
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Cadmium ions form complexes with primary amines and with 1,2-diaminoethane. Cd2++ 4CH3NH2[Cd(CH3NH2)4]2+Kstab = 3.6 × 106 equilibrium I Cd2++ 2H2NCH2CH2NH2[Cd(H2NCH2CH2NH2)2]2+Kstab = 4.2 × 1010 equilibrium II Write an expression for the stability constant, Kstab, for equilibrium I, and state its units. Kstab = units Cadmium ions are poisonous and need to be removed from some water supplies. This is often done by adding a complexing agent. In a sample of ground water the concentration of Cd2+is 1.00 × 10–4 mol dm–3. Calculate the concentration of CH3NH2needed to reduce the concentration of Cd2+in this dilute solution by a factor of one thousand. concentration of CH3NH2= mol dm–3 Values for ∆H o and ∆G o for equilibria I and II, and the value of ∆S o for equilibrium I, are given in the table below. All values are at a temperature of 298 K. equilibrium ∆H o / kJ mol–1 ∆G o / kJ mol–1 ∆S o / J K–1 mol–1 I –57.3 –37.4 –66.8 II –56.5 –60.7 to be calculated Suggest a reason why the ∆H o values for the two equilibria are very similar. Calculate ∆S o for equilibrium II. ∆S o = J K–1 mol–1 Suggest a reason for the difference between the ∆S o you have calculated for equilibriumII and that for equilibrium I given in the table. Which of the two complexes is the more stable? Give a reason for your answer.
7. Equilibria  →  7.1. Chemical equilibria: reversible reactions, dynamic equilibrium
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Esterases are enzymes that hydrolyse esters. R C + H2O + HO–R' O O R' R C O O H Enzymes can be quite specific in the structures of the substrates they act upon. For example, an esterase isolated from the mould Aspergillus niger will hydrolyse phenyl ethanoate, CH3CO2C6H5, but not its isomer methyl benzoate, C6H5CO2CH3. Outline how enzymes catalyse reactions, and explain their specificity. Use diagrams in your answer where appropriate. Sample bottles of each of the isomers phenylethanoate and methylbenzoate have lost their labels and so have been named isomer A and isomer B. The carbon-13 NMR spectra of isomers A and B contain the following peaks. isomer A isomer B δ 52 δ 26 δ 128 δ 122 δ 129 δ 126 δ 130 δ 129 δ 133 δ 151 δ 167 δ 169 The identity of the compound responsible for each spectrum can be deduced by studying the chemical shifts (δ) of the peaks in the spectra. Use the Data Booklet to assign the correct peaks to the labelled carbon atoms in the structures of the isomers below. Write each value next to the relevant carbon atom and hence deduce the identity of each isomer. C CH3 O O methyl benzoate is isomer O CH3 C O phenyl ethanoate is isomer These two isomers are difficult to distinguish chemically. Describe a method of converting them to suitable products in step 1 which can then be tested in step 2. You should state the reagents and conditions for each step, and any observations you would make. step 1 step 2
18. Carboxylic acids and derivatives  →  18.2. Esters
21. Organic synthesis  →  21.1. Organic synthesis
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Amino acids can be separated by electrophoresis. Draw a labelled diagram of the apparatus used to separate a mixture by electrophoresis. Explain the principles of the separation of amino acids by electrophoresis. Electrophoresis is usually carried out in a buffer solution. Given three buffers, with pH values of 2.0, 7.0 and 12.0, suggest, with a reason, which buffer would be the most suitable for the separation of the following amino acid mixtures. Your reasons should refer to the structure of each molecule. (The structures of these amino acids are given in the Data Booklet.) Asp and Val buffer pH reason Lys and Ser buffer pH reason Tyr and Phe buffer pH reason Draw the structure of the dipeptide Gly-Ser, showing the peptide bond in full. The infra-red spectrum of Gly-Ser is shown below. transmittance wavenumber / cm–1 E F G Use the Data Booklet to identify the bond in the molecule of Gly-Ser that is responsible for each of the peaks indicated on the above infra-red spectrum. E F G
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
11. Group 17  →  11.4. The reactions of chlorine
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Describe and explain the trend in the solubility of the hydroxides down Group 2. Calcium reacts vigorously with HCl producing H2. Ca+ 2HCl → CaCl 2+ H2How would you expect the enthalpy change for this reaction to compare with the enthalpy change for the reaction where HNO3is used in place of HCl but all other conditions are the same? Explain your answer. The ionic equation for this reaction is shown. Ca+ 2H+→ Ca2++ H2∆H o = x kJ mol–1 Construct a fully labelled Hess’ Law cycle to connect each side of this equation to the relevant gas phase ions. Use your cycle, the following data, and data from the Data Booklet, to calculate a value for x. standard enthalpy of atomisation of Ca, (Ca) +178 kJ mol–1 standard enthalpy of hydration of Ca2+, (Ca2+) –1576 kJ mol–1 standard enthalpy of hydration of H+, (H+) –1090 kJ mol–1 x = kJ mol–1 The standard enthalpy change for the reaction between Caand CH3CO2His less negative than x by 2 kJ mol–1. Suggest an explanation for this.
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
5. Chemical energetics  →  5.2. Hess’s law
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The anti-inflammatory drug ibuprofen can be synthesised from benzene via the following six steps. step 1 step 5 step 2 step 3 H J step 4 OH CN CO2H step 6 CO2H ibuprofen Draw circles around any chiral carbon atoms in the above five formulae. Suggest the structures of compounds H and J and draw them in the boxes above. Suggest reagents and conditions for steps 1-6. step 1 step 2 step 3 step 4 step 5 step 6 Name the mechanism of step 1 and state the type of reaction for step 6. step 1 step 6
21. Organic synthesis  →  21.1. Organic synthesis
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Complete the electronic configuration of the iron atom. Fe 1s22s22p6 In some of its complexes, the Fe3+ ion has only one unpaired electron in its d orbitals. Using the symbols ↑ and ↓ to represent electrons of opposite spins, complete the following diagram to show the d orbital electronic configuration of this Fe3+ ion. 3d energy A solution containing a mixture of Sn2+and Sn4+is added to a solution containing a mixture of Fe2+and Fe3+. Use E o data from the Data Booklet to predict the reaction that might take place when the two solutions are mixed, and write an equation for the reaction. Hexaaquairon(ions are pale violet. They form a colourless complex with fluoride ions, F–, equilibrium 1, and a deep-red complex with thiocyanate ions, SCN–, equilibrium 2. [Fe(H2O)6]3+ + F– [Fe(H2O)5F]2+ + H2O equilibrium 1 Kstab = 2.0 × 105 mol–1 dm3 violet colourless [Fe(H2O)6]3+ + SCN– [Fe(H2O)5SCN]2+ + H2O equilibrium 2 Kstab = 1.0 × 103 mol–1 dm3 violet deep-red Predict and explain the sequence of colour changes you would observe in each of the following experiments. • A few drops of KSCNare added to 5 cm3 of Fe3+, followed by a few drops of KF. • A few drops of KFare added to 5 cm3 of Fe3+, followed by a few drops of KSCN. What type of reaction is occurring during the experiments in ?
1. Atomic structure  →  1.3. Electrons, energy levels and atomic orbitals
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