chemistry-class-12-unit-06-chapter-03-isolation-of-metals-l-3-3-4p-gx4t1igi

<h4 id="successelectrolytic-cell-for-the-extraction-of-aluminiumsuccess-2"><Success>Electrolytic cell for the extraction of aluminium</Success></h4>
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<ul>
<li>The oxygen liberated at anode reacts</li>
<li>Carbon of anode produces CO and $CO_2$</li>
<li>For each kg of Al about 0.5 kg of C anode is burnt</li>
<li>The electrolytic reactions are</li>
</ul>
<p><strong>Cathode</strong>$\quad$ $Al^{3+}(melt)+3e \rarr Al(l)$</p>
<p><strong>Anode</strong>$\quad$ $C(s)+O^{2-}(melt) \rarr CO(g)+2e^-$</p>
<p>$C(s)+2O^{2-}(melt) \rarr CO(g)+4e^-$</p>
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<h4 id="successcopper-extraction-by-hydrometallurgysuccess"><Success>Copper extraction by hydrometallurgy</Success></h4>
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<ul>
<li>
<p>Used for low grade ores</p>
</li>
<li>
<p>Ore is leached out using acid</p>
</li>
<li>
<p>The solution containing $Cu^{2+}$ is treated with scrap iron or $H_2$</p>
<p>$Cu^{2+}(aq)+H_2(g) \rarr Cu(s)+2H^+(aq)$</p>
<p>$Cu^{2+}(aq)+Fe(s) \rarr Cu(s)+Fe^{2+}(aq)$</p>
</li>
<li>
<p>Iron in the electrochemical series is above Cu</p>
</li>
</ul>
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<h3 id="successmethods-of-metal-extractionsuccess"><Success>Methods of metal extraction</Success></h3>
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<p><strong>Distillation</strong></p>
<ul>
<li>Very useful for low boiling metals like zinc and mercury</li>
<li>The impure metal is evaporated</li>
<li>Pure metal obtained as distillate</li>
</ul>
<p><strong>Liquation</strong></p>
<ul>
<li>Useful for low melting metal like tin</li>
<li>Molten metal is made to flow on a slopped floor</li>
<li>In separates from higher melling impurities</li>
</ul>
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<h3 id="successmethods-of-metal-extractionsuccess-1"><Success>Methods of metal extraction</Success></h3>
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<p><strong>Electrolytic refining</strong></p>
<ul>
<li>Impure metal is made anode</li>
<li>A strip of the same metal in pure form is used as cathode</li>
<li>They are put in a suitable electrolytic bath containing soluble salt of the same metal</li>
<li>The more basic metal remains in the solution and the less basic ones go to the anode mud</li>
<li>The reactions are</li>
<li>Anode $M \rarr M^{n+}+ne^-$</li>
<li>Cathode $M^{n+}+ne^- \rarr M$</li>
</ul>
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<h3 id="successrefiningsuccess-1"><Success>Refining</Success></h3>
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<p><strong>Refining of copper by an electrolytic method</strong></p>
<ul>
<li>Anodes are of impure copper and pure copper strips are taken as cathode electrolyte is acidified solution of copper sulphate</li>
<li>Electrolysis results in the transfer of copper in pure form from the anode to the cathode</li>
<li>Anode $Cu \rarr Cu^{2+}+2e^-$</li>
<li>Cathode $Cu^{2+}+2e^- \rarr Cu$</li>
<li>Impurities Sb, Se, Te, Ag, Au and Pt from the blister Cu deposit as anode mud</li>
<li>Recovery of these elements may meet the cost of refining</li>
<li>Zinc may also be refined this way</li>
</ul>
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<h3 id="successrefiningsuccess-3"><Success>Refining</Success></h3>
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<p><strong>Zone refining</strong></p>
<ul>
<li>Molten zone moves along with the heater moved forward</li>
<li>As the heater moves forward , the pure metal crystallises</li>
<li>From melt and the impurities pass on into adjacent molten zone</li>
<li>Process is repeated several times moving heater in the same direction</li>
<li>At one end , impurities get concentrated</li>
<li>This end is cut off Method is very useful for producing semiconductor and other metals of very high purity , example Ge , Si , B , Ga , In</li>
</ul>
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<h3 id="successrefiningsuccess-4"><Success>Refining</Success></h3>
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<p><strong>Vapour phase refining</strong></p>
<ul>
<li>Metal is converted into its volatile compound and collected</li>
<li>It is then decomposed to give pure metal</li>
<li>Two requirements are</li>
</ul>
<p>(i) The metal should form a volatile compound with an available reagent</p>
<p>(ii) The volatile compound should be easily decomposable , so that the recovery is easy</p>
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<h3 id="successrefiningsuccess-5"><Success>Refining</Success></h3>
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<p><strong>Mond process for refining nickel</strong></p>
<ul>
<li>Nickel is heated in a stream of cartion monoxide</li>
<li>Result a votatile complex , nickel tetracarbonyl</li>
<li>$Ni+4CO \rarr Ni(CO)_4(330-350 K)$</li>
<li>Ni carbonyl on heating to 450-470 K</li>
<li>Decompose giving the pure metal</li>
<li>$Ni(CO)_4 \rarr Ni+4CO$</li>
</ul>
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<h3 id="successrefiningsuccess-6"><Success>Refining</Success></h3>
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<p><strong>Van arkel method for refining zirconium or titanium</strong></p>
<ul>
<li>It is very useful for removing all the oxygen and nitrogen present in the form of impurity in metals like Zr and Ti</li>
<li>The crude metal is heated in an evacuated vessel with $l_2$</li>
<li>The metal iodide being more covalent , volatilizes</li>
</ul>
<p>$Zr+2I_2 \rarr ZrI_4$</p>
<ul>
<li>The metal iodide is decomposed on a tungsten filament , electrically heated to about 1800K</li>
<li>The pure metal is deposited on the filament</li>
</ul>
<p>$ZrI_4 \rarr Zr+2I_2$</p>
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