Al₂O₃ is reduced by electrolysis at low potentials and high currents. If 4.0 × 10⁴ amperes of current is passed through molten Al₂O₃ for 6 hours, what mass of aluminium is produced? (Assume 100% current efficiency. At. mass of Al = 27 g mol^-1)

8.1 × 10⁴ g
2.4 × 10⁵ g
1.3 × 10⁴ g
9.0 × 10³ g

Solution

Given:
(i)Cu²⁺ + 2e^– ⟶ Cu, E°= 0.337V
(ii)Cu²⁺ + e^– ⟶ Cu⁺, E° = 0.153V Electrode potential,
E° for the reaction,Cu⁺ + e^– ⟶ Cu, will be :

0.90 V
0.30 V
0.38 V
0.52 V

Solution

Standard free energies of formation (in kJ/mol) at 298 K are– 237.2, –394.4 and – 8.2 for H₂O(l), CO₂(g) and pentane (g),respectively. The value E°cell for the pentane-oxygen fuel cell is :

1.968 V
2.0968 V
1.0968 V
0.0968 V

Solution

Kohlrausch’s law states that at :

finite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte.
infinite dilution each ion makes definite contribution to equivalent conductance of an electrolyte depending on the nature of the other ion of the electrolyte.
infinite dilution, each ion makes definite contribution to conductance of an electrolyte whatever be the nature of the other ion of the electrolyte.
infinite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte.

Solution

Kohlrausch’s Law states that at infinite dilution, each ion migrates independent of its co-ion and contributes to the total equivalent conductance of an electrolyte a definite share which depends only on its own nature.From this definition we can see that option (d) is the correct answer.

On the basis of the following E° values, the strongest oxidizing agent is :
[Fe(CN)₆]^4- ⟶ [Fe(CN)₆]^3- + e^– ; E° = -0.35V
Fe²⁺ ⟶ Fe³⁺ + e^–; E° = -0.77V

[Fe(CN)₆]^4-
Fe²⁺
Fe³⁺
[Fe(CN)₆]^3-

Solution

From the given data we find Fe³⁺ is strongest oxidising agent.More the positive value of E°, more is the tendency to get oxidized. Thus correct option is (c).

The efficiency of a fuel cell is given by