9. Metals
A section of Chemistry, 0620
Listing 10 of 1272 questions
Iron is extracted from its ore, hematite, in the blast furnace. slag molten iron air firebrick lining waste gases raw materials: coke, C limestone, CaCO3 hematite, Fe2O3 The temperature inside the blast furnace can rise to 2000 °C. Write an equation for the exothermic reaction which causes this high temperature. Carbon monoxide is formed in the blast furnace. This reduces the ore hematite, Fe2O3, to iron. Explain how carbon monoxide is formed in the blast furnace. Write an equation for the reduction of hematite by carbon monoxide. Explain why it is necessary to add limestone, calcium carbonate, to the blast furnace. Include an equation in your explanation. Most of the iron from the blast furnace is converted into mild steel. A method of preventing the steel from rusting is coating it with zinc. What is the name of this method of rust prevention? Explain, using the idea of electron transfer, why zinc-coated steel does not rust even when the coating is scratched and the steel is in contact with oxygen and water.
0620_w12_qp_32
THEORY
2012
Paper 3, Variant 2
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Hydrogen chloride is an acidic gas. Complete the dot and cross diagram to show the electronic structure of hydrogen chloride. H Cl Is hydrogen chloride a covalent or an ionic compound? Give a reason for your answer. Hydrogen chloride reacts with water to form hydrochloric acid. Which one of the following is the most likely pH of hydrochloric acid? Put a ring around the correct answer. pH 2 pH 7 pH 9 pH 14 Hydrochloric acid reacts with both metal oxides and carbonates. Complete the word equation for the reaction of hydrochloric acid with calcium carbonate. hydrochloric + calcium → + + acid carbonate Complete the symbol equation for the reaction of magnesium oxide with hydrochloric acid. Name the salt which is formed. MgO + HCl → MgCl 2 + H2O name of salt A student reacted magnesium with hydrochloric acid to fi nd out how concentration affects the rate of reaction. The magnesium was in excess. He measured the volume of hydrogen produced at various time intervals. The graph shows his results. volume of hydrogen / cm3 time / seconds At what time had the reaction just fi nished? What volume of hydrogen gas is given off during the fi rst 50 seconds of the reaction? volume of hydrogen cm3 The student repeated the experiment. State two factors, apart from the concentration of hydrochloric acid, that should be kept constant when repeating the experiment. 1. 2.
0620_w13_qp_21
THEORY
2013
Paper 2, Variant 1
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Zirconium (Zr) is a metal in Period 5. Its main oxidation state is +4. The following are all zirconium atoms: 90Zr , 91Zr and 92Zr . In terms of numbers of electrons, neutrons and protons, how are these three atoms the same and how are they different? They are the same because They are different because Containers for fuel rods in nuclear reactors are made of zirconium. Nuclear reactors are used to produce energy and to make radioactive isotopes. Which isotope of a different element is used as a fuel in nuclear reactors? State one medical and one industrial use of radioactive isotopes. Above 900 °C, zirconium reacts with water to form zirconium(oxide, ZrO2, and hydrogen. Write an equation for this reaction. In a nuclear accident, water may come in contact with very hot zirconium. Explain why the presence of hydrogen inside the reactor greatly increases the danger of the accident. It is possible to determine whether zirconium(oxide is acidic, neutral, basic or amphoteric using an acid and an alkali. Complete the table of possible results. If the oxide is predicted to react write ‘R’, if it is predicted not to react write ‘NR’. if the oxide is predicted result with hydrochloric acid predicted result with aqueous sodium hydroxide acidic neutral basic amphoteric
0620_w13_qp_33
THEORY
2013
Paper 3, Variant 3
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The main uses of zinc are preventing steel from rusting and making alloys. The main ore of zinc is zinc blende. Zinc blende consists mainly of zinc sulfi de, ZnS. There are two major methods of extracting zinc from its ore. They are the direct reduction of zinc oxide to zinc and by electrolysis. In both methods, zinc oxide is made from the zinc sulfi de in the ore. How is zinc oxide made from zinc sulfi de? Write an equation for the reaction used to reduce zinc oxide to zinc. In the electrolytic method, zinc oxide reacts with sulfuric acid to form impure aqueous zinc sulfate. This solution contains Ni2+, Co2+ and Cu2+ ions as impurities. Write the equation for the reaction between zinc oxide and sulfuric acid. Nickel, cobalt and copper are all less reactive than zinc. Explain why the addition of zinc powder removes these ions from the solution. The solution of zinc sulfate is electrolysed using inert electrodes. This electrolysis is similar to that of copper(sulfate with inert electrodes. Write the equation for the reaction at the negative electrode . Complete the equation for the reaction at the positive electrode . OH– → 2H2O + + e– The electrolyte changes from zinc sulfate to Brass is an alloy of copper and zinc. Suggest two reasons why brass is often used in preference to copper. Sacrifi cial protection is a method of rust prevention. Explain in terms of electron transfer why steel, which is in electrical contact with zinc, does not rust.
0620_w13_qp_33
THEORY
2013
Paper 3, Variant 3
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Questions Discovered
1272