9701_w18_qp_23
A paper of Chemistry, 9701
Questions:
4
Year:
2018
Paper:
2
Variant:
3
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Iron pyrite, FeS2, has a yellow colour that makes it look like gold metal. The compound contains the ions Fe2+ and S2 2–. Give the full electronic configuration of Fe2+. 1s2 Calculate the oxidation number of sulfur in the S2 2– ion. Assume that each sulfur atom in the ion has the same oxidation number.  oxidation number of sulfur in the S2 2– ion = Describe the metallic bonding in gold. Iron pyrite is often called fool’s gold because of its appearance. Impure samples of iron pyrite often contain a small amount of gold. The gold can be obtained from impure iron pyrite. The impure iron pyrite is roasted in oxygen, to produce iron(oxide and sulfurdioxide. Gold does not react with oxygen. The sulfurdioxide produced during roasting would cause environmental consequences if released into the atmosphere. State and explain one of these environmental consequences. Complete the equation to show the roasting of iron pyrite in oxygen. 4FeS2 + 2Fe2O3 +  A sample of impure iron pyrite was roasted in oxygen. The composition of the mixture of solid products is shown. solid product mass / g Fe2O3 33.18 Au 0.37 Calculate the mass of FeS2 present in the sample of impure iron pyrite. Assume that all the FeS2 was converted to Fe2O3 during the roasting process. (Mr: FeS2, 120.0; Fe2O3, 159.6)  mass of FeS2 = g Use your answer to to calculate the percentage by mass of gold in this sample of impure iron pyrite. Assume that gold is the only impurity in this sample of impure ironpyrite. Give your answer to two significant figures. (If you were unable to calculate an answer to , use 55.00 g as the mass of FeS2 in this calculation. This is not the correct answer.)  percentage by mass of gold = % 
10. Group 2  →  10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
2. Atoms, molecules and stoichiometry  →  2.4. Reacting masses and volumes (of solutions and gases)
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Nitrogen, N2, is an inert gas that makes up 78% of the Earth’s atmosphere. Explain why nitrogen is inert. Draw a ‘dot-and-cross’ diagram of a nitrogen molecule. Show outer electrons only.  Nitrogen, N2, and oxygen, O2, react together in the air during lightning strikes to form nitrogen monoxide, NO. Explain why the reaction of N2 and O2 occurs during lightning strikes. Write two equations to suggest how the NO formed reacts further to create nitric acid, HNO3.  Nitrate fertilisers are used to provide nitrogen for plant growth. Uncontrolled use of these can cause a reduction in animal and plant life in natural water supplies. Explain how uncontrolled use of nitrate fertilisers can cause this problem. Some soils have compounds such as ammonium nitrate, calcium carbonate and calcium hydroxide added to them. Suggest why calcium hydroxide is added to some soils. When calciumhydroxide reacts with compounds containing the ammonium ion, NH4 +, a gas is produced. State the identity of this gas and explain why the reaction occurs. gas explanation  Another fertiliser, calcium ammonium nitrate, is formed when solid calcium carbonate is added to a mixture of aqueous ammonium nitrate and dilute nitric acid. Suggest what would be observed in this reaction. Calcium nitrate decomposes at a higher temperature than calcium ammoniumnitrate. Write an equation for the thermal decomposition of calcium nitrate. 
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
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Trihalomethanes are organic molecules in which three of the hydrogen atoms of methane are replaced by halogen atoms, for example CHCl 3. CHCl 3 is a colourless liquid with a high vapour pressure. Explain what is meant by high vapour pressure. An important reaction of CHCl 3is the manufacture of CHCl F2, using the following reversible reaction. CHCl 3+ 2HFCHCl F2+ 2HCl Use the data to calculate the enthalpy change of reaction, ΔHr , for the formation of CHCl F2as shown in the equation. compound enthalpy change of formation, ΔHf / kJ mol–1 CHCl 3–103.2 CHCl F2– 482.2 HF–273.3 HCl –92.3  enthalpy change of reaction, ΔHr = kJ mol–1 The reaction in is carried out using a heterogeneous catalyst. Explain fully the meaning of the terms heterogeneous and catalyst. heterogeneous catalyst  CHCl F2 was used as an alternative to chlorofluorocarbons (CFCs). CHCl F2 should no longer be used because it was found to contribute to the enhanced greenhouse effect. Give the meaning of the term enhanced greenhouse effect. Explain how CHCl F2may contribute to this effect. Suggest another environmental problem associated with the use of CHCl F2. CHCl F2 is also used to produce the monomer tetrafluoroethene, C2F4. This monomer can be used to produce poly, PTFE. State the type of polymerisation that occurs during the production of PTFE. Draw the repeat unit of PTFE.  Suggest why PTFE is used as a coating for cooking pans. Waste disposal can cause litter problems. State two other difficulties associated with the disposal of PTFE.  
8. Reaction kinetics  →  8.3. Homogeneous and heterogeneous catalysts
14. Hydrocarbons  →  14.2. Alkenes
15. Halogen compounds  →  15.1. Halogenoalkanes
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The structure of glycolic acid is shown. glycolic acid H H C O C OH OH Complete the table to show what you would observe when an aqueous solution of glycolicacid is added separately to each of the reagents. If a reaction occurs, state the functional group of glycolic acid that is responsible for the reaction. reagent observation with glycolic acid does a reaction occur? / functional group Na2CO32,4-DNPH acidified Cr2O7 2–  Two reaction sequences to make glycolic acid are shown. HCHO CH2(OH)CO2H sequence A X HCN and NaCN reaction 1 reaction 2 CH3CO2H CH2BrCO2H CH2(OH)CO2H sequence B Br2 reaction 3 reaction 4 Draw the structure of X.  Name the reagent for reaction2. Name the mechanism of reaction3. Suggest the essential condition for reaction3. Reaction4 occurs via an SN2 mechanism. Complete the diagram for the mechanism for reaction4. Include all relevant charges, partial charges, curly arrows and lone pairs. H H C O C OH –OH Br H H C O C OH OH  Glycolic acid can also be made by reacting glyoxylicacid with NaBH4. H H C O C OH OH C C glyoxylic acid O OH H O NaBH4 glycolic acid State the role of NaBH4 in this reaction. Write an equation for this reaction using molecular formulae. Use [H] to represent NaBH4. When glycolicacid is heated in the presence of a sulfuricacid catalyst, a new compound, Y, C4H4O4, is formed. The equation for the reaction is given. 2CH2(OH)CO2H C4H4O4 + 2H2O glycolic acid Y The infra-red spectrum of Y is shown. transmittance wavenumber / cm–1 State how this spectrum differs from an infra-red spectrum of glycolicacid. Explain your answer with particular reference to the peaks within the range 1500 – 4000 cm–1. Suggest a structure for Y.  
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
18. Carboxylic acids and derivatives  →  18.1. Carboxylic acids
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