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Friday, August 8, 2014

Metal and Nonmetal class 10th Solved Questions



Question: Why is froth floatation process selected for concentration of the sulphide ore?

Ans. : Sulphide ore particles are welted by oil (pire oil) and gangue particles by water]

Question: Why cannot Al be reduced by carbon?

Ans. Aluminium is stronger reducing agent than carbon and therefore, cannot be reduced by it.

Question: Name the common elements present in the anode mud in electrolytic refining of copper. Why are they so present?

Ans. The anode mud in the electrolytic refining of copper contains antimony, selenium tellurium, silver, gold and platinum. These are present as impurities in blister copper. They are less reactive and are not affected by CuSO4-H2SO4 solution and hence settle down near anode as anode mud.

Question: Which is the cheapest and most abundant reducing agent which is used in, the extraction of metals?

Ans. Carbon in the form of coke.

Question: What is the significance of leaching in the extraction of aluminium ?

Ans. The principal ore of aluminium is bauxite (Al203). It contains Si02, iron oxides, titanium oxide as impurities. The significance of leaching in the extraction of aluminium from bauxite is to remove the impurities from the ore.

Question: What is the role of graphite rod in the electrometallurgy of aluminium?

Ans. The graphite rod is useful in the electrometallurgy of aluminium for reduction of alumina to aluminium. ;  
    
 2Al203+ 3C → 4Al + 3C02

Question: Write chemical reactions taking place in the extraction of zinc from zinc blende.

Ans. (i) The concentrated zinc blende ore (ZnS) is roasted in the presence of excess air about
1200  to convert it to zinc oxide.

2ZnS                  +         3O2    →    2ZnO            +         2S02

Zinc blende                                        Zinc oxide
(ii) Zinc oxide is reduced to zinc by heating with crushed coke at 1673 K

ZnO + C →Zn + CO

(iii) The impure copper is refined by electro refining method. In this method, the impure zinc is made anode and a plate of pure zinc is made cathode in an electrolytic bath containing zinc sulphate and a small amount of  dilute H2SO4. On passing current, the following reaction occur:

At anode: Zn →  Zn2+ + 2e-

At cathode: Zn2+ + 2e- →Zn

The zinc gets deposited on cathode and is collected.   

Question: What are the different methods of the purification of metals

Answer: 
PURIFICATION OR REFINING OF METALS

The metal obtained by any of the above methods is impure and is known as crude metal. The process of purifying the crude metal is called refining. The method of refining depends upon the nature of the metal and the impurities which are present in the metal. Some of the methods generally applied for refining metals are discussed below.

Liquation: 

This process is used for refining the metals having low melting points. Such as tin, lead, bismuth. etc. this is based on the principle that the metal to be refined is easily fusible (melt easily) but the impurities do not fuse easily. In this process, the impure metal is placed on the sloping hearth of the furnace and is gently heated. The hearth is maintained at a temperature slightly above the melting point of the metal. The metal melts and flows down to the bottom of sloping hearth and the impurities are left behind. The pure metal is collected to the bottom of the sloping hearth. 

Distillation:
This method is used for the purification of volatile metals (which form vapours readily). Such as mercury and zinc. In this method the impure metal is heated strongly in a vessel (called retort). The pure metal distils over and its vapours  are condensed separately in a receiver to get pure metal. The non- volatile impurities are left behind in the retort.

Oxidation method (Oxidative refining):

This method is used for the refining of metal in those cases in the impurities have greater tendency to get oxidised than metal itself.
For example: Impure iron (Pig or cast iron) is refined oxidative refining method. Pig iron contains carbon, sulphur, phosphorous, silicon and manganese as impurities. When a blast of air is blown over molten pig iron these impurities are oxidised to their oxides (CO2, SO2, P2O5 etc.) and get removed. The pure iron is left behind. Similarly, Silver is refined by this method.

Electrolytic refining:

This is the most widely method for the refining of impure metals. Many metals such as copper, zinc, tin, nickel, silver, gold etc. are refined electrolytically. It is based upon the phenomenon of electrolysis, in this process, the impure metal is made of the anode and a thin strip of pure metal is made of the cathode. A solution of the metal salt is used as an electrolyte. On passing the electric current through the electrolyte. The pure metal from the anode dissolved into electrolyte. An equivalent amount of pure metal gets deposited on the cathode. The soluble impurities go into the solution, whereas, the impurities settle down at the bottom of the anode and are known as anode mud.

For example: In the electrolytic refining of copper (The apparatus is set up as shown in figure as below) crude copper is made the anode, a thin sheet of pure copper is made the cathode. The electrolyte is a solution of copper sulphate containing a small amount of dilute H2SO4 acid. On passing the electric current copper dissolve from the anode into the electrolyte. An equivalent amount of copper is deposited at the cathode in the from pure at metal. The following reactions occurs at the electrodes.

1 comment:

J Sunil said...

Bioleaching is the extraction of metals from their ores through the use of living organisms. This is much cleaner than the traditional heap leaching using cinema.[1] Bioleaching is one of several applications within biohydrometallurgy and several methods are used to recover copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.

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