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 Multiple Choice QuestionsLong Answer Type

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91. Give reasons:
(i) Zinc and not copper is used for the recovery of silver from the complex [Ag (CN)2]

(ii) Pine oil is generally added in the froth floatation process.

(iii) Graphite is used as anode but not diamond.

(iv) In the metallurgy of iron, lime stone is added to the ore.

(v) Reduction of metal oxides by aluminium becomes faster just after ignition of mixture.


(i) Zinc is a very powerful reducing agent and readily displaces silver present in the complex.

Zn+2Ag(CN)2-       [Zn(CN4)2-Soluble + 2Ag](ppt)

Copper is also more reducing than silver but is not so effective as zinc. Moreover, zinc is cheaper than copper. Also the by product formed by zinc (zinc cynaide) is easliy disposable.

(ii) In the froth floatation process, sulphide ore is to be separated from gangue or earthy impurities. The impure ore is mixed with water and pine oil in a tank and steam is passed through it. Now gangue particles are wetted by water while the ore by oil. With the help of steam, the sulphide ore rises in the form of a foam while the gangue impurities settle at the bottom of the container.

(iii) In graphite, these are free electrons present in the layers which help in electrical conductivity. But in diamond, no free electrons are present. As such diamond is a bad conductor of electricity and diamond can not constitute anode.

(iv) In the metallurgy of iron, lime stone (CaCO3) acts as a flux and forms calcium silicate CaSiO3 (slag).

CaCO3  CaO + CO2(g)
CaOflux + SiO2     CaSiO3slag

(v) The reaction possesses exothermic nature and huge amount of heat released during the course of reaction makes it fast.

Fe2O3+ 2Al → Al2O3 + 2Fe ΔH = –ve
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92.

Explain different methods of reduction of the roasted/calcined ore to the metallic form.

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93. Describe the methods, generally used to refine metals.
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 Multiple Choice QuestionsFill In the Blanks

94.

The impurities present in minerals are called ______________.

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95.

Cassiterite is an ore of ___________.

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96.

Calamine is an ore of ________.

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97.

Aluminium is obtained from Al2O3 by_________reduction.

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98.

In the metallurgical process for the electrorefining of the metal the anode is made of _________ metal.

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99.

In the Bessemer converter during the extraction of copper, the substance responsible for forming blister is  ___________.

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100.

During the extraction, the metallic silver is precipitated by the addition of __________ to ________

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