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General Principles And Processes of Isolation Of Elements

Short Answer Type

51.

Give reason for the following: Although aluminium is above hydrogen in the electro-chemical series, it is stable in air and water.

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52.

An ore example of galena (PbS) is contaminated with zinc blende (ZnS). Name one chemical which can be used to concentrate galena selectively by froth floatation method.

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53.

Out of C and CO, which is better reducing agent at 673 K?

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54.

Why copper matte is put in silica lined converter?

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55.

Suggest a condition under which magnesium could reduce alumina.

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56. Although thermodynamically feasible, in practice, magnesium metal is not used for the reduction of alumina in the metallurgy of aluminium, why?

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57.
Why reduction of a metal oxide becomes easier if the metal formed is in liquid state at the temperature of reduction?

The entropy is higher if the metal is in liquid state than when it is in solid state. The value of entropy change (ΔS) of the reduction process is more on +ve side when the metal formed is in liquid state and the metal oxide being reduced is in solid state. Thus the value of ΔG° becomes more on negative side and the reduction becomes easier.

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58.

If at any site, low grade copper ores are available and zinc and iron scraps are also available. Which of the two scraps would be more suitable for reducing the leached copper ore and why?

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