General Principles and Isolation of Elements

31. Option (i)

Below point A, only the value of ΔG (CO, CO₂) is less than the value of ΔG (Fe, FeO) at the corresponding temperatures. Thus, only carbon monoxide will be able to reduce FeO to Fe and will get itself oxidized into CO₂.

30. Option (iv)

Above point A, ΔG (C, CO)

29. Option (i) 

The cyanide process involves 3 steps:

First step - The finely grounded ore of gold and silver are made to come in contact with the solution containing the cyanide,

Second step - it involves separation of gold and silver from the cyanide solution  

Third step - it involves the recovery of gold and silver in their pure forms precipitating the remaining solution with zinc dust.

Thus, the metal is recovered by displacing Zn with the metal (Au or Ag) from metal ions.

28. Option (i)

The electrolytic method can be used to purify zinc and copper. The impure metal is used as an anode in this method. As the cathode, a pure strip of the same metal is used. They are immersed in an appropriate electrolytic bath containing a soluble salt of the same metal.

The more basic metals remain in the solution, while the less basic metals are transferred to the anode mud.

27. Option (ii)

Reaction involved in the metallurgy of aluminum is 2Al₂O₃ + 3C→ 4Al + 3CO₂.

The reaction at cathode is Al³⁺ + 3e⁻→ Al

The reaction at anode is

C+12O₂ →CO + 2e and C+O₂→CO₂ + 4e⁻

Hence, from the reaction graphite anode is oxidized to carbon monoxide and carbon dioxide.

26. Correct option (i)

The reaction at the anode with a lower E $°$  value is preferred, but oxygen cannot be obtained in this process due to overvoltage.

25. Option (iii)

Reaction takes place as Cu₂O + $\frac{1}{2}$ Cu₂S?3Cu +12SO₂ with a product as bristle copper. This type of reaction is called an auto-reduction reaction as copper is reducing itself with help of other copper compounds.

24. Option (ii)

Purification of metal crystals by making a thin region of crystal undergo melting is known as Zone refining. The molten crystal is then moved up along the crystal to get pure form of it. This process is used to get pure form of Silicon and Germanium. Basic principle of the zone refining process is that the impurities are more soluble in molten metal than solid metal to get pure form of metal.

23. Option (i)

Explanation: Aluminum is the third most abundant metal in the earth's crust (8.3 percent approximately by weight). It is found in a variety of igneous minerals, including mica and clays. The second most abundant metal in the earth's crust is iron.

22. Option (iv)

Copper (I) oxide is reduced by copper (I) sulfide in this reaction. Because copper is reduced by itself in this process, it is referred to as auto reduction.