0620_w09_qp_32
A paper of Chemistry, 0620
Questions:
7
Year:
2009
Paper:
3
Variant:
2
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For Examiner's Use An important ore of zinc is zinc blende, ZnS. How is zinc blende changed into zinc oxide? Write a balanced equation for the reduction of zinc oxide to zinc by carbon. A major use of zinc is galvanizing; steel objects are coated with a thin layer of zinc. This protects the steel from rusting even when the layer of zinc is broken. thin layer of zinc steel exposed to oxygen and water steel Explain, by mentioning ions and electrons, why the exposed steel does not rust. For Examiner's Use Zinc electrodes have been used in cells for many years, one of the first was the Daniel cell in 1831. zinc electrode copper electrode zinc sulfatecopper(sulfateporous pot - stops solutions from mixing V voltmeter Give an explanation for the following in terms of atoms and ions. observation at zinc electrode – the electrode becomes smaller explanation observation at copper electrode – the electrode becomes bigger explanation When a current flows, charged particles move around the circuit. What type of particle moves through the electrolytes? Which particle moves through the wires and the voltmeter?
9. Metals  →  9.5. Corrosion of metals
4. Electrochemistry  →  4.1. Electrolysis
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For Examiner's Use The distinctive smell of the seaside was thought to be caused by ozone, O3. Ozone is a form of the element oxygen. A mixture of oxygen and ozone is formed by passing electric sparks through oxygen. 3O2 2O3 Suggest a technique that might separate this mixture. Explain why this method separates the two forms of oxygen. technique explanation Ozone is an oxidant. It can oxidise an iodide to iodine. 2I– + O3 + 2H+ → I2 + O2 + H2O What would you see when ozone is bubbled through aqueous acidified potassium iodide? Explain in terms of electron transfer why the change from iodide ions to iodine molecules is oxidation. Explain, using your answer to b, why ozone is the oxidant in this reaction. For Examiner's Use It is now known that the smell of the seaside is due to the chemical dimethyl sulfide, (CH3)2S. Draw a diagram that shows the arrangement of the valency electrons in one molecule of this covalent compound. Use x to represent an electron from a carbon atom. Use o to represent an electron from a hydrogen atom. Use ● to represent an electron from a sulfur atom. Name the three compounds formed when dimethyl sulfide is burnt in excess oxygen.
6. Chemical reactions  →  6.4. Redox
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
12. Experimental techniques and chemical analysis  →  12.5. Identification of ions and gases
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For Examiner's Use The first three elements in Group IV are carbon, silicon and germanium. The elements and their compounds have similar properties. The compound, silicon carbide, has a macromolecular structure similar to that of diamond. A major use of silicon carbide is to reinforce aluminium alloys which are used in the construction of spacecraft. Suggest three of its physical properties. Draw a diagram to show the arrangement of silicon atoms around one carbon atom in silicon carbide. Label this diagram 1. Draw a diagram to show the arrangement of carbon atoms around one silicon atom in silicon carbide. Label this diagram 2. Germanium(oxide, GeO2, has the same macromolecular structure as silicon(oxide. Draw the structural formula of germanium(oxide. For Examiner's Use Germanium forms a series of hydrides comparable to the alkanes. Draw the structural formula of the hydride which contains three germanium atoms per molecule. Predict the products of the complete combustion of this hydride.
2. Atoms, elements and compounds  →  2.6. Giant covalent structures
8. The Periodic Table  →  8.1. Arrangement of elements
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For Examiner's Use Sulfuric acid is made by the Contact process. 2SO2 + O2 2SO3 This is carried out in the presence of a catalyst at 450 °C and 2 atmospheres pressure. Sulfur dioxide is made by burning sulfur. Name a source of sulfur. Give another use of sulfur dioxide. Name the catalyst used. If the temperature is decreased to 300 °C, the yield of sulfur trioxide increases. Explain why this lower temperature is not used. Sulfur trioxide is dissolved in concentrated sulfuric acid. This is added to water to make more sulfuric acid. Why is sulfur trioxide not added directly to water? For Examiner's Use Sulfuric acid was first made in the Middle East by heating the mineral, green vitriol, FeSO4.7H2O. The gases formed were cooled. FeSO4.7H2O→ FeSO4+ 7H2Ogreen crystals yellow powder 2FeSO4→ Fe2O3+ SO2+ SO3On cooling SO3 + H2O → H2SO4 sulfuric acid SO2 + H2O → H2SO3 sulfurous acid How could you show that the first reaction is reversible? Sulfurous acid is a reductant. What would you see when acidified potassium manganate(is added to a solution containing this acid? Suggest an explanation why sulfurous acid in contact with air changes into sulfuric acid. 12.16 g of anhydrous iron(sulfate was heated. Calculate the mass of iron(oxide formed and the volume of gases, at r.t.p., formed. 2FeSO4 → Fe2O3+ SO2+ SO3mass of one mole of FeSO4 = 152 g number of moles of FeSO4 used = number of moles of Fe2O3 formed = mass of one mole of Fe2O3 = g mass of iron(oxide formed = g total number of moles of gases formed = total volume of gases formed = dm3
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
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For Examiner's Use Butan-1-ol is used as a solvent for paints and varnishes, to make esters and as a fuel. Butan-1-ol can be manufactured from but-1-ene, which is made from petroleum. Biobutanol is a fuel of the future. It can be made by the fermentation of almost any form of biomass - grain, straw, leaves etc. But-1-ene can be obtained from alkanes such as nonane, C9H20, by cracking. Give the reaction conditions. Complete an equation for the cracking of nonane, C9H20, to give but-1-ene. C9H20 → Name the reagent that reacts with but-1-ene to form butan-1-ol. Balance the equation for the complete combustion of butan-1-ol. C4H9OH + O2 → CO2 + H2O Write a word equation for the preparation of the ester butyl propanoate. For Examiner's Use The fermentation of biomass by bacteria produces a mixture of products which include biobutanol, propanol, hydrogen and propanoic acid. Draw the structural formula of propanol and of propanoic acid. Show all the bonds. propanol propanoic acid Why is it important to develop these fuels, such as biobutanol, as alternatives to petroleum? How could you show that butanol made from petroleum and biobutanol are the same chemical?
11. Organic chemistry  →  11.2. Naming organic compounds
11. Organic chemistry  →  11.3. Fuels
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