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As per the Ellingham diagram, above 1350, the standard Gibbs free energy of formation  of  is lower than the  from . So, that's why above  ,  can reduce MgO.
Vapour phase refining-  In this process metal is converted into its volatile compound which is collected and decomposed to give pure metals. Two major requirement- The metal should form a volatile compound with the suitable reagent. the volatile compound should be easily decomposable so that to recover easily  
Electrolytic refining- It is a process of refining impure metals by electricity. In this method, impure metal is act as anode and the same pure metal strip is act as cathode. Same metal salt which is soluble is taken as the electrolyte. When electricity is passed the metal ions deposited at the cathode (pure metal) and the impure metal is starting dissolving in the solution in the form of ions....
ZONE REFINING-  This method is based on that the impurities are more soluble in the molten state than n the solid state. In this process, a circular mobile heater surrounding the rod of impure metal is fixed at one end. Move the heater from one end to another end so that the impurities present in the rod also moves to the other end of the rod. Repeat the process several times again and again....
In Down's process, we prepare sodium metals in which chlorine is obtained as a by-product. It involves electrolysis of a fused mixture of  and . Sodium is deposited at cathode and chlorine at anode as a by-product. At Cathode -  At anode-   If an aqueous solution of NaCl is subjected to electrolysis, dihydrogen gas  is evolved at the cathode while chlorine  is obtained at the anode.
From the graph we can observe that, a mtal oxide can reduce the oxide of other metals,if the  of the first oxide is more than the second oxide. example-  can reduce  to Zn but Zn cannot reduce  because   of   from Mg is more negative.
The Gibbs free energy formation of  from   is always higher than the Gibbs free energy of formation of . Thus CO cannot reduce . On the other hand, Gibbs free energy of formation of  from C is less than gibbs free energy of formation of . Hence C can easily reduce  to zinc.
  ......................... (-827 KJ/mol) .........................  (-540 KJ/mol) _________________________________          (On substracting )       ...............(-287 KJ/mol)                                                        In the above reaction, we see that  of formation of Cr is negative (-287 KJ/mol) Hence the reduction of   with aluminium is possible.
According to the Ellingham diagram, the standard Gibbs free energy of formation of  from  is lower than the formation of  from CO. So, therefore, CO cannot reduce   to zinc ().
In case of low-grade ores, copper is extracted by hydrometallurgy. Leaching is done with the help of acid or bacteria in the presence of air. The solution containing  is treated with scrap iron or dihydrogen . 
The main purpose of adding cryolite in metallurgy of aluminium is- To increase the electrical conductivity of the alumina   To decrease the melting point of the mixture  
The copper matte composed of  and . It is put in a silica-lined converter to remove the remaining ferrous oxide () and ferrous sulphide () present in copper matte as slag () Some silica is also added and hot air blast is blown to convert the remaining  to the metallic copper.  
Minerals are the naturally occurring substance which contains some amount of metals. They are found in the earth crust and obtained by mining. Ores are the specific minerals in which metals are economically extracted. It has a definite composition. Each and every ore is a mineral but not every mineral is ore.
The iron that obtains from the blast furnace is pig iron. it contains 4% carbon and many impurities like .  Cast iron is obtained from pig iron by melting pig iron with scrap iron and coke using hot air blast. It contains slightly less carbon content around 3% and it is hard an brittle.
Roasting- The process of converting sulphide ore to oxide. In this process, the ore is heated in the furnace with a regular supply of air, below its melting temperature: example- sulphide ore of zinc, lead, and copper. Calcination- Process of converting hydroxide and carbonate ore to oxide in a limited supply of air. The temperature should be below the metals melting point in this...
The separation of alumina carried out in the following steps- The powdered ore is treated with the concentrated  solution at 473K-523K and 35-36 bar pressure. The  gas is passed through the resulting solution to neutralise the aluminate, which results in ppt. of hydrated alumina.  The obtained hydrated alumina is filtered, dried and heated to get pure alumina.  
Nickel is refined by Mond's Process, in which Nickel is heated in steam in presence of Carbon monoxide () to form nickel carbonyl complex . The complex is volatile in nature. This complex is decomposed at high temperature to get a pure nickel.
Zone refining is the method for an element in which impurities present have chemical properties close to the properties of those elements.
Chromatographic method of refining is particularly suitable if the element is obtained in minute quantity.
The role of silica in metallurgy of copper is to remove the  (iron oxide) produced during roasting as slag. If the sulphide ore contains iron, it mixed with silica () as flux before heating.   combines with silica and produce iron silicate ()