Zinc alloys have been used for over 2500 years. Explain the phrase zinc alloy. Making alloys is still a major use of zinc. State one other large scale use of zinc. Describe the bonding in a typical metal, such as zinc, and then explain why it is malleable. You may use a diagram to illustrate your answer. Suggest why the introduction of a different atom into the structure makes the alloy less malleable than the pure metal. Zinc metal is made by the reduction of zinc oxide. The major ore of zinc is zinc blende, ZnS. Zinc blende contains silver and lead compounds as well as zinc sulfi de. Zinc blende is converted into impure zinc oxide by heating it in air. 2ZnS + 3O2 → 2ZnO + 2SO2 Describe how zinc oxide is reduced to zinc. Some of the zinc oxide is dissolved in sulfuric acid to make aqueous zinc sulfate. Write a balanced symbol equation for this reaction. This impure solution of zinc sulfate contains zinc ions, silver(ions and lead ions. Explain why the addition of zinc powder produces pure zinc sulfate solution. Include at least one ionic equation in your explanation. Describe how zinc metal can be obtained from zinc sulfate solution by electrolysis. A labelled diagram is acceptable. Include all the products of this electrolysis. The electrolysis is similar to that of copper(sulfate solution with inert electrodes. 0620_w12_qp_33 THEORY 2012 Paper 3, Variant 3 View
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 View