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 Multiple Choice QuestionsShort Answer Type

141.

Give reasons for the following observations:

Leather gets hardened after tanning

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142.

Give reasons for the following observations:

Lyophilic sol is more stable than a lyophobic sol.

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143.

Indicate the principle behind the method used for the refining of zinc.

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144.

What is the role of silica in the extraction of copper?

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145.

Which form of the iron is the purest form of commercial iron?

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146.

Which reducing agent is employed to get copper from the leached low-grade copper ore?

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147.

Outline the principles behind the refining of metals by the following methods:

Zone refining method

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148.

Outline the principles behind the refining of metals by the following methods:

Chromatographic method 

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149.

Name the method used for the refining of Nickel metal?

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150.

Which solution is used for the leaching of silver metal in the presence of air in the metallurgy of silver? 


Dilute solution of NaCN and KCN is used for leaching of silver metal in the presence of air in the metallurgy of silver, for example in the following reaction

 

AgS + 4NaCN ⇌ 2Na[Ag(CN)2] + Na2SAgS + 4NaCN  ⇌  2Na[Ag(CN)2] + Na2S

 

The solution of sodium Argento cyanide combines with zinc dust and forms sodium tetra cyanozicate and precipitated silver. This precipitated silver is called spongy silver.

 

Zn+2Na[Ag(CN)2] →  Na2[Zn(CN)4] + 2AgZn + 2Na[Ag(CN)2] → Na2[Zn(CN)4] + 2Ag

 

The spongy silver is fused with potassium nitrate to obtain pure silver. Then the silver obtained is purified by an electrolytic process.

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