Thursday, August 9, 2012

X Metals and Non-Metals Solved Important Guess Questions

Metals and Non-Metals Solved Important  Guess Questions
Q1. Define allotropy. Name the two common allotropes of phosphorus.
Ans:  Allotropy : "Existence of an element in two or more distinct forms which have different physical properties but same chemical properties is called allotropy and the forms are called allotropes."
Q.2 .Write four differences in the properties of the two allotropes of phosphorus.
Ans: Two allotropes of phosphorus are white phosphorus and red phosphorus.
Red phosphorus
White phosphorus
(i) It has an opaque red colour.
(i) It is colourless, but appears yellow when kept in atmosphere.
(ii) It sublimes at 400ºC.
(ii) Its melting point is 44ºC.
(iii) It is less reactive.
(iii) It is very reactive.
(iv) It combines with chlorine only on heating.
(iv) It combines with chlorine spontaneously.
Q.3.Why do allotropes of phosphorus show different properties?
They show different properties as the bonding between yellow phosphorus is weak while in red phosphorus is strong.
Q4. How does iron occur in nature?  
Ans 2. Iron occurs in nature in combined states mainly it occurs in oxide and sulphide ores.
Oxide-ores :    Haematite : Fe2O3    Magnetite : Fe3O4    Limonite : Fe2O3.3H2O
Sulphide-ores : Iron pyrites : FeS2     Carbonate ores : Siderite : FeCO3
The various steps involved in the extraction of iron metal from its oxide ore (haematite) (Fe2O3) are given below :
(i) Concentration of ore : The iron ore haematite (Fe2O3) is concentrated by crushing the ore and washing it in a stream of water. This removes most of the gangue.
(ii) Calcination : The washed iron is then strongly heated in the absence of air (calcinied) to expel water sticking to it.
(iii) Reduction : The iron oxide ore (haematite) is mixed with coke and lime stone and put into a blast furnace near its bottom.
The following chemical reaction takes place in blast furnace :
(a) Coke present in blast furnace burns insufficent air to form carbon monoxide (which acts as reducing agent)
2C (Carbon) + O2 (Oxygen) ------à  2CO (Carbon monoxide)
(b) Carbon mono oxide reduces iron (III) oxide to iron metal.
Fe2O3 (Iron oxide) + 3CO (Carbon mono oxide) ----à  2Fe (Iron metal) + 3CO2 (Carbon dioxide)
The molten iron collects at the bottom of blast furnace.
(c) The lime stone decomposes to form calcium oxide and carbon dioxide due to intense heat in the blast furnace.
CaCO3 (Calcium carbonate) ---Heat-à CaO (Calcium oxide) + CO2 (Carbon dioxide)
(d) This calcium oxide reacts with silicon dioxide (sand) present as impurity in the ore to form liquid calcium silicate called slag
CaO (Calcium oxide) + SiO2 (Silicon dioxide) ------> CaSiO3 (Calcium silicate)
The molten slag collects on the top of the molten iron and is separately taken out
Q.5. State the differences between (i) iron and steel (ii) stainless steel and steel.
Ans: Differences :
(i) (a) Iron is an element which don't contain any impurities while steel is an alloy of iron with 1.5% of carbon
(b) Pure iron is not very hard and strong while steel is very hard and strong.
(ii) Stainless steel is alloy of iron with chromium and nickel while steel is alloy of iron with carbon.
Q6. State the three major steps usually involved in the metallurgical processes.
Ans3. The major steps usually involved in the metallurgical processes are (i) concentration of ore (ii) conversion of concentrated ore into metal oxide (iii) Reduction of metal oxide to metal (iv) Refining of impure metal.
Q.7. Name the chief ore of aluminum. Describe the necessary chemical equations how aluminum is extracted from this ore.
The main ore of aluminium is Bauxite(Al2O3.2H2O)
The various steps involved in the extraction of aluminium metal from its bauxite ore are given below :
Purification : The bauxite ore usually contains iron oxide and silica (sand) as impurities which are removed by Baeyer's method as follows :
Bauxite (Al2O3)is dissolved in a hot concentrated solution of sodium hydroxide to form sodium aluminate (NaAlO2). The iron oxide and other impurities do not dissolve and are removed by filtration.
Al2O3 + 2NaOH  ------>2NaAlO2 + H2O
Sodium aluminate is mixed with water and cooled. This gives a precipitate of aluminium hydroxide
NaAlO2  + 2H2O -------> Al(OH)3 + NaOH

When aluminium hydroxide is strongly heated it gives pure aluminium oxide or alumina
2Al(OH)3 --------> Al2O3 + 3H2O (Water)
Electrolytic reduction of pure aluminium oxide :
 Al2O3 is reduced to aluminium in a specially made electrolytic cell as shown in Fig. given below. In this cell the inside coke lining acts as a cathode and carbon rod is used as an anode. The cell is charged with a mixture of concentrated purified Al2O3 and cryolite (Na3AlF6). Cryolite is mixed to lower down the melting temperature of alumina. When the current is passed through the cell, mixture melts because of the heat generated due to the resistance offered by the mixture. The molten mixture is then electrolysed at the bottom of the cell.
Al2O3 ----Electrolysis------>2Al3+ + 3O2-
The aluminium thus obtained is further purified by electrolytic refining.
Q8. Describe the extraction of Cu from its ore by:
(i) concentration (ii) Roasting (iii) Reduction (iv) Refining of crude metal.
Ans4. The main ores of copper are copper pyrites (CuFeS2) and copper glance (Cu2S). The various steps usually involved are given below :
Concentration : Concentration is done by froth-floatation. The finely powdered ore is mixed with water and pine oil in large tank. The ore particles are wetted by the oil, whereas the gangue particles are wetted by water. Air is blown through the mixture. As a result oil froth containing ore particles is formed which floats on the top of the water and can be skimmed off easily.
Roasting : The concentrated ore is roasted. Roasting is done in reverberatory furnace.
2CuFeS2 + O2 -------
àCu2S + 2FeS + SO2­
Cu2S and FeS are partially oxidized.
2Cu2S + 3O2 -------
à 2Cu2O + 2SO2
2FeS. + 3O2 --------
à 2FeO + 2SO2­
Reduction : Takes place in Bassemer converter. It can be tiled in any position. It has a basic lining inside.
The little FeS present in matte is completely oxidized to FeO and then changed into slag with reaction of silica. Cuprous sulphide reacts with Cu2O to form blister copper.
Cu2S + 2Cu2O --------> 6Cu + SO
Refining of copper : The impure copper metal is purified by the process of electrolytic refining to get pure copper metal.
The impure metal is made the anode and a strip of pure copper cathode. These are immersed in a copper sulphide solution with a little sulphuric acid added to it. On passing an electric current the anode begins to dissolve pure copper gets deposited on the cathode. The impurities either dissolves in the solution or deposited below the anode as anode mud.
At anode : Cu (Copper) --------->Cu2+ (copper ion)
At cathode : Cu2+ (Copper ion) -------->Cu (Copper atom) deposits on cathode
Thus pure copper is obtained at the cathode.
Q9.  What is rusting of iron?

Ans5. Rusting : The process of eating away of metal, by the action of atmospheric reagents changing the metal  into its compounds is called as rusting.
When iron is kept to environment, a red coloured layer is formed on its surface it is rust and the process is known as rusting.
The rusting of iron is :
(i) 2Fe (Iron) + O2 (Oxygen) + H2O (Water)-----à 2Fe(OH)2 (Iron hydroxide)
(ii) Fe(OH)2 + O2 + H2O ------à2Fe2O3.3H2O (Rust)
Necessary conditions for rusting are :
(i) Presence of moisture
(ii) Presence of air

10. Write any two common methods to prevent rusting.

Prevention of Rusting :
(i) Rusting is prevented by galvanization. It is a process of coating Zinc metal over iron by electro plating.
(ii) It is prevented by painting the surface of metal and coating the surface of metal with oil or grease

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