Chemistry

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.

10. Mn has half-filled 3d⁵ electrons and Zn has fully-filled 3d¹⁰ electrons which give them extra stability and they both resist to lose electrons and get reduced. 

The E? value also depends on the hydration enthalpy. More negative is the enthalpy of hydration, high is the E? value. This is the reason behind Mn, Ni and Zn are having higher E? value than expected

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.

9. Copper lies below hydrogen in electrochemical series which means it has positive standard reduction potential i.e.   + 0.34 V. and hence cannot liberate hydrogen from acids.

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.

8. KMnO₄ K₂MnO₄ +    MnO₂ + O₂

  (A)                           (B)          (C)

MnO₂ +  KOH → 2K₂MnO₄ +  2H₂O

MnO₂ +  4NaCl  +  4H₂SO₄→ MnCl₂ +  2NaHSO₄+2H₂O  +  Cl₂

  (D) 

(A)  =  KMnO₄

(B)  = K₂MnO₄

(C)  =  MnO₂

(D)  =  MnCl₂ 

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.

7. (A) 2I^-  + S₂O₈^2-  →Fe (III) I₂ +  2SO₄^2- 

 role of fe ions:

2Fe³⁺  +  2I^- → 2Fe²⁺  + I₂

2Fe²⁺  + S₂O₈^2- → 2Fe³⁺  +  2SO₄^2-  

(B) 1. Fine powdered state of Nickel is used in the hydrogenation of oils into fats. 

2. Iron is used in the formation of ammonia in Haber's process. 

3. In contact process in manufacture of H₂SO₄, vanadium is used in its oxide form- V₂O₅.

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.