Editing Content :: Admin Scraper

Chapter

Content type

Position

Value

agents because they can displace metals of lower reactivity from their compounds. For example, when manganese dioxide is heated with aluminium powder, the following reaction takes place – 3MnO (s) + 4Al(s) → 3Mn(l) + 2Al O (s) + Heat 2 2 3 Can you identify the substances that are getting oxidised and reduced? These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state. In fact, the reaction of iron(III) oxide (Fe O ) 2 3 with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the thermit reaction. Fe2O 3s) + 2Al(s) → 2Fe(l) + A2 3 (s) + Heat 3.4.5 Extracting Metals towards the Top of the Figure 3.11 Activity Series Thermit process for The metals high up in the reactivity series are very reactive. They cannot joining railway tracks be obtained from their compounds by heating with carbon. For example, carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc., to the respective metals. This is because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. For example, sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides. The metals are deposited at the cathode (the negatively charged electrode), whereas, chlorine is liberated at the anode (the positively charged electrode). The reactions are – + – At cathode Na + e → Na At anode 2Cl – → Cl +22e – Similarly, aluminium is obtained by the electrolytic reduction of aluminium oxide. 3.4.6 Refining of Metals The metals produced by various reduction processes described above are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining. Electrolytic Refining: Many metals, such as copper,zinc, tin, nickel, silver, gold, etc., are refined electrolytically. In Figure 3.12 this process, the impure metal is made the anode and a Electrolytic refining of copper. The thin strip of pure metal is made the cathode. A solution of electrolyteisasolutionofacidifiedcopperthe metal salt is used as an electrolyte. The apparatus is sulphate. The anode is impure copper, whereas, the cathode is a strip of pureset up as shown in Fig. 3.12. On passing the current copper. On passing electric current, purerough the electrolyte, the pure metal from the anode copper is deposited on the cathode. dissolvesintotheelectrolyte.Anequivalentamountofpure 52 Science Reprint 2026-27