Give reasons for the following observations:

Leather gets hardened after tanning

Give reasons for the following observations:

Lyophilic sol is more stable than a lyophobic sol.

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

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

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

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

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

Zone refining method

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

Chromatographic method 

Name the method used for the refining of Nickel metal?

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