9701_w15_qp_43
A paper of Chemistry, 9701
Questions:
9
Year:
2015
Paper:
4
Variant:
3
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1
The dissolving of an ionic compound in water is accompanied by an energy change, the enthalpy change of solution, ∆H sol. MgCl 2+ aq → Mg2++ 2Cl –Describe, in terms of bond breaking and bond making, what happens to the solid ionic lattice when an ionic compound dissolves in water. What is meant by the term enthalpy change of solution, ∆H sol? Use the following data to calculate the standard enthalpy change of hydration, , of chloride ions, Cl –. You may find it helpful to construct an energy cycle. enthalpy change value (Mg2+) –1925 kJ mol–1 lattice energy of MgCl 2–2524 kJ mol–1 enthalpy change of solution for MgCl 2–155 kJ mol–1 (Cl –) = kJ mol–1 The enthalpy change of hydration for Na+, (Na+), is –410 kJ mol–1. Suggest an explanation for why the of the Na+ ion is less exothermic than the of the Mg2+ ion. Describe and explain how the solubility of the Group II sulfates varies down the group.
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
4. States of matter  →  4.2. Bonding and structure
3. Chemical bonding  →  3.2. Ionic bonding
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Cobalt is a transition element and forms compounds with oxidation numbers +2 and +3. Complete the electronic structures for a cobalt atom, 1s22s22p6 cobalt in the +3 oxidation state. 1s22s22p6 In an aqueous solution of cobalt(sulfate the cobalt forms complex ions. What is meant by the term complex ion? State two chemical properties of cobalt, other than the formation of complexes, that are not shown by a typical s-block element. Cobalt(ions, Co2+, show some chemical properties similar to those of copper(ions, Cu2+. Use this information and the Data Booklet to suggest the formula of the cobalt species formed in each of the following reactions. State the type of reaction taking place in each case. formula of cobalt species formed type of reaction Co2++ an excess of NH3Co2++ OH–Co2++ S2O8 2– Some transition elements are present in superconductors. These are materials that conduct electricity with little or no resistance. Compound Q is a superconductor and contains 13.4% yttrium, 41.2% barium, 28.6% copper and 16.8% oxygen by mass. Show that the empirical formula of Q is YBa2Cu3O7. Show all your working. The table shows the oxidation numbers of yttrium, barium and oxygen in Q. element oxidation number yttrium +3 barium +2 oxygen –2 Calculate the average oxidation number of copper in Q. Hence deduce the oxidation number of each of the three copper atoms in Q.
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
6. Electrochemistry  →  6.1. Redox processes: electron transfer and changes in oxidation number (oxidation state)
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Chlorine gas and iron(ions react together in aqueous solution as shown. Cl 2+ 2Fe2+→ 2Cl –+ 2Fe3+Complete and label the diagram to show how the standard cell potential, , for the above reaction could be measured at standard conditions. Use the Data Booklet to calculate the for this reaction. What colour change would you see when chlorine gas is bubbled through a solution containing Fe2+ions until the reaction is complete? Predict the effect, if any, of decreasing the concentration of Cl –on the magnitude of the cell potential in . Explain your answer. A fuel cell is an electrochemical cell that can be used to generate electrical energy. In the alkaline hydrogen-oxygen fuel cell, H2and O2are passed over two inert electrodes immersed in an alkaline solution. Write the half-equations for the reactions taking place at each of these electrodes. hydrogen electrode oxygen electrode Construct an equation for the overall reaction. Suggest one possible advantage of using a hydrogen-oxygen fuel cell over a conventional ‘simple cell’ battery.
11. Group 17  →  11.4. The reactions of chlorine
14. Hydrocarbons  →  14.2. Alkenes
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On the grid below, sketch the trend in the melting points of the Group IV elements. The point for germanium has already been shown. melting point C Si Ge Sn Pb Suggest an explanation of this trend in terms of structure and bonding of the Group IV elements. GeO2, SnO2 and PbO2 are amphoteric oxides. What is meant by the term amphoteric? Construct an equation for the reaction of SnO2 with NaOH. By quoting information from the Data Booklet explain why the reaction between Cr2O7 2–ions and acidified Sn2+ions is feasible. Construct an equation for the reaction in and give any relevant observations. equation observations On heating, germanium(oxide disproportionates to form germanium(oxide and germanium. Describe, using this reaction as an example, what is meant by a disproportionation reaction. Some of the reactions of cyanogen, NC–CN, are similar to those of chlorine, Cl –Cl. On treatment with cold, aqueous sodium hydroxide, cyanogen disproportionates in a similar manner to chlorine. Complete the equation for this reaction. (CN)2 + NaOH → + + Draw a ‘dot-and-cross’ diagram for NC–CN. Show the outer electrons only. At room temperature, phosphorus atoms form P4 molecules rather than P2 molecules. The phosphorus molecule, P4, has a cage-like structure containing only P–P single bonds. All the phosphorus atoms in P4 are trivalent. Suggest a structure for P4. At a temperature of 1200 K P2 and P4 exist in equilibrium in the gas phase. P2 molecules contain the P≡P bond. The average bond energy of P–P is 198 kJ mol–1 while that of P≡P is 489 kJ mol–1. Use the above bond energies to calculate the enthalpy change, ∆H, for the following reaction. 2P2→ P4 When phosphorus(chloride, PCl 5, is reacted with ammonium chloride, NH4Cl, hydrogen chloride gas, HCl, is released and a product with the molecular formula P3N3Cl 6 is formed. Construct an equation for this reaction. P3N3Cl 6 has a cyclic structure containing alternating phosphorus and nitrogen atoms in the ring system. All the nitrogen atoms are trivalent and all the phosphorus atoms are pentavalent. Suggest a structure for P3N3Cl 6.
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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A student carries out some reactions with separate samples of butanal and butanone. H O butanal O butanone The following results are obtained with reagents L, M and N. ( means a reaction takes place.) reagent butanal butanone L   M  no reaction N no reaction  Suggest a possible identity for each reagent L, M and N. L M N Give the structure of the organic product formed when M reacts with butanal. What is observed when N reacts with butanone? What type of reaction is occurring when N reacts with butanone? The organolithium compound methyl lithium, CH3Li, can act as a source of CH3 – ions. CH3Li CH3 – + Li+ The CH3 – ion can act as a nucleophile. The reaction between methyl lithium and carbonyl compounds can be used to make alcohols. Suggest a mechanism for the reaction of butanal with CH3 – ions. Include all necessary curly arrows, lone pairs and relevant dipoles. intermediate step 1 H+ CH3 – CH2CH2CH3 C H O CH2CH2CH3 CH3 C H OH A chemist decides to prepare the following organic compound G from butanal. CH3 CH3 H3C OH G Draw the structure of the organolithium reagent which could be used to prepare G from butanal.
16. Hydroxy compounds  →  16.1. Alcohols
15. Halogen compounds  →  15.1. Halogenoalkanes
18. Carboxylic acids and derivatives  →  18.1. Carboxylic acids
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4-nitrophenol can be converted into a range of useful organic products. OH O2N 4-nitrophenol 4-nitrophenol can react with three different reagents. Complete the table by: • drawing the structures of the organic products formed, • identifying the non-organic products formed. reagent organic product structure identity of non-organic product NaBr2CH3COCl 4-nitrophenol can also be used in the synthesis of the dye Mordant Brown by the following route. In step 2 of this synthesis, 4-nitrophenol reacts with intermediate F made from amine E. Assume that the –SO3 – Na+ group does not react. + OH NO2 E (C6H8N3SO3Na) F step 1 step 2 OH NO2 N N SO3 – Na+ H2N NH2 Mordant Brown Suggest structures for compounds E and F and draw them in the boxes above. Suggest reagents and conditions for step 1, step 2.
21. Organic synthesis  →  21.1. Organic synthesis
19. Nitrogen compounds  →  19.2. Nitriles and hydroxynitriles
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DNA is an important biochemical molecule. DNA has a double helical structure that consists of two strands linked together. Draw a block diagram of DNA showing two repeat units in each strand. Label all the components, showing and labelling the bonds between the strands. Genetic information is stored in DNA. Outline the main steps in the replication of DNA. DNA fingerprinting is based on the fact that all humans (apart from genetically identical twins) have different DNA base sequences. This is regularly used to help investigate serious crimes. The first stage of DNA fingerprinting requires a sample of DNA to be broken down into shorter fragments. What could be used to carry out this fragmentation? Name the analytical technique used to separate these short fragments. After the fragments have been separated, what could the DNA fingerprint be treated with to reveal the position of the bands? A sample of blood, thought to be from the suspect, was found at a crime scene. The DNA of the blood sample, and that of four possible suspects, was analysed. blood stain suspect suspect suspect suspect Based on this evidence, circle the suspect who should be arrested. suspect 1 suspect 2 suspect 3 suspect 4
20. Polymerisation  →  20.1. Addition polymerisation
13. An introduction to AS Level organic chemistry  →  13.4. Isomerism: structural isomerism and stereoisomerism
14. Hydrocarbons  →  14.2. Alkenes
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A mixture of volatile organic compounds X, Y and Z can be separated in a gas chromatograph. Their identities can be confirmed by measuring their different retention times and comparing to known values. A gas chromatogram is shown. absorption X Y Z time / mins Suggest what is meant by the term retention time. Give an example of a carrier gas used in gas chromatography. Z spends the longest time in the chromatography column. Suggest why this might be the case. Explain a possible limitation of gas / liquid chromatography in separating two esters such as ethyl methanoate, HCO2CH2CH3, and methyl ethanoate, CH3CO2CH3. A student works out the areas underneath the three peaks in the chromatogram. peak X Y Z area / mm2 Assuming the areas underneath the peaks are proportional to the masses of the respective components, what percentage of the original mixture was made up of the organic compound, X? % of X = The NMR spectrum of Y given below shows four absorptions. absorption δ / ppm What compound is responsible for the absorption at δ = 0? Compound Y is an ester with the molecular formula C4H8O2. Complete the table for the NMR spectrum of Y. The actual chemical shifts for three absorptions in Y and the splitting pattern for the resonance at δ = 3.7 ppm have been given for you. Use of the Data Booklet may be helpful. chemical shift δ / ppm type of protonnumber of protons splitting pattern 1.0 2.3 3.7 singlet Use your conclusions to suggest a structure for the ester Y.
22. Analytical techniques  →  22.2. Mass spectrometry
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To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series. Prodrugs are compounds that are inactive, but are easily converted in the body to the active drug by enzyme hydrolysis. Compound W is a prodrug. O O O NH2 H2N CH3 W Complete the molecular formula for W. C H34N O Compound W contains a benzene ring in its structure. Name three other functional groups in W. On the diagram above, use an arrow to indicate the bond that would be hydrolysed. Draw the structures of the likely products of the enzyme hydrolysis of compound W. What features of the molecule W make it water soluble? Explain your answer.
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
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