Chemistry Class 12 NCERT Solutions: Chapter 6 General Principles and Processes of Isolation of Elements Part 4

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Q: 17. Why copper matte is put in silica-lined converter?

Answer:

Copper matte contains . Copper matter is put in a silica-lined converter to remove the remaining present in the matte as slag . Also, some silica is added to the silica-lined converter. Then, a hot air blast is blown. As a result, the remaining are converted to iron silicate is converted into metallic copper.

Q: 18. What is the role of cryolite in the metallurgy of aluminium?

Answer:

Cryolite has two roles in the metallurgy of aluminium:

1. To decrease the melting point of the mixture from to .

2. To increase the electrical conductivity of

Q: 19. How is leaching carried out in case of low-grade copper ores?

Answer:

In case of low grade copper ores, leaching is carried out using acid or bacteria in the presence of air. In this process, copper goes into the solution as ions.

The resulting solution is treated with scrap iron or to get metallic copper.

Q: 20. Why is zinc not extracted from zinc oxide through reduction using ?

Answer:

The standard Gibbs free energy of formation of from

is lower than that of from . Therefore, cannot reduce to . Hence, is

not extracted from through reduction using .

Q: 21. The value of for formation of is and that of is . Is the reduction of possible with ?

Answer:

The value of for the formation of from is higher than that of from . Therefore, Al can reduce to . Hence, the reduction of with Al is possible.

Alternatively,

Subtracting equation (ii) from (i), we have

As for the reduction reaction of by is negative, this reaction is possible

Q: 22. Out of and , which is a better reducing agent for ?

Answer:

Q 22 A Better Reducing Agent

Q 22 a Better Reducing Agent

Q 22 A Better Reducing Agent

Reduction of is usually carried out at . From the above figure, it can be observed that above , the Gibbs free energy of formation of from and above , the Gibbs free energy of formation of from is lesser than the Gibbs free energy of formation of . Therefore, can easily reduce . On the other hand, the Gibbs free energy of formation of from is always higher than the Gibbs free energy of formation of . Therefore, cannot reduce .

Hence, C is a better reducing agent than CO for reducing ZnO.