Electrochemical Cells

Step 1: Concept
Cell potential is the difference between reduction potentials: .
Step 2: Analysis
From given data:
(i) .
(ii) .
Subtracting (i) from (ii) gives: .
Step 3: Conclusion
The resulting emf is .
Final Answer: (C)

Step 1: Concept
Cell potential is the difference between reduction potentials: .
Step 2: Analysis
From given data:
(i) .
(ii) .
Subtracting (i) from (ii) gives: .
Step 3: Conclusion
The resulting emf is .
Final Answer: (C)

Step 1: Concept
Reducing agent strength is directly related to the negative value of standard reduction potential.
Step 2: Analysis
A higher negative potential indicates a greater tendency to lose electrons (undergo oxidation).
Step 3: Conclusion
Among the given values, Zinc has the highest negative potential ( ), making it the strongest reducing agent.
Final Answer: (A)

Step 1: Concept
Reducing agent strength is directly related to the negative value of standard reduction potential.
Step 2: Analysis
A higher negative potential indicates a greater tendency to lose electrons (undergo oxidation).
Step 3: Conclusion
Among the given values, Zinc has the highest negative potential ( ), making it the strongest reducing agent.
Final Answer: (A)

Step 1: Identify Cathode and Anode
For the reaction : is reduced (cathode) and is oxidized (anode).
Step 2: Formula
.
Step 3: Calculation
.
Final Answer: (d)

Step 1: Phasor Concept
In a series RC circuit, the voltages across the resistor ( ) and capacitor ( ) are out of phase.
Step 2: Vector Sum
Total voltage .
Step 3: Calculation
V.
Final Answer: (a)

Step 1: Concept
Fraction remaining , where is the number of half-lives.
Step 2: Analysis
3 hours = 180 min. Number of half-lives .
Fraction remaining .
Step 3: Conclusion
Fraction decayed .
Final Answer: (B)

Step 1: Rydberg Formula
.
Step 2: Ground State
For ground state, and . So, .
Step 3: Solve for n
. Taking the reciprocal and square root: .
Final Answer: (a)

Step 1: Concept
A higher negative value of standard reduction potential ( ) indicates a stronger reducing power.
Step 2: Analysis
The order of values (reducing power) is:
Step 3: Conclusion
Mg can reduce both and . Zn can reduce , but it cannot reduce . Iron (Fe) can neither reduce Mg nor Zn, but it can oxidise them. Thus, statement (A) is correct.
Final Answer: (A)

Step 1: Understanding the ionic conductance at infinite dilution.
The equivalent conductance at infinite dilution for a salt like BaCl is the sum of the ionic conductances of the ions:

Step 2: Substituting the given values.
Given
and,
,
we add them:


Step 3: Conclusion.
The correct answer is (2) 203

Step 1: Understanding the Standard Electrode Potential.
The standard electrode potential of the Normal Hydrogen Electrode (NHE) is defined as 0.00 V at 298 K. This is the reference value against which other electrode potentials are measured.

Step 2: Explanation of the options.
- (1) 0.05 V: This is not the value for NHE.
- (2) 0.10 V: This is not the value for NHE.
- (3) 0.50 V: This is not the value for NHE.
- (4) 0.00 V: This is the correct standard electrode potential for NHE.

Step 3: Conclusion.
The correct answer is (4) 0.00 V.

Step 1: Understanding the Nernst equation.
The Nernst equation relates the standard electrode potential (E°) to the equilibrium constant (K) for a reaction: For two-electron change reactions:

Step 2: Substituting values.
At 25°C, , , and using the known constants: Solving for , we get:

Step 3: Conclusion.
The correct answer is (2) .

Step 1: Formula / Definition}

Step 2: Calculation / Simplification}
Sodium fusion converts and to (thiocyanate).
(blood red colour).
Step 3: Final Answer

Step 1: Formula / Definition}

Step 2: Calculation / Simplification}
-cresol + + (ortho-hydroxy aldehyde)
+ (cyanohydrin)
+ ( -hydroxy acid, chiral)
Step 3: Final Answer

Step 1: Formula / Definition}

Step 2: Calculation / Simplification}
(ortho-hydroxy benzaldehyde): intramolecular H-bonding lower boiling point, more volatile.
(para-isomer): intermolecular H-bonding higher boiling point, less volatile.
is more volatile than .
Step 3: Final Answer

Concept:

Step 1: Fe Fe = oxidation (anode).

Step 2: O OH = reduction (cathode).

Step 3: Substitute values:

Step 4: Conclusion:
Cell potential = +0.84 V

Concept: Faraday constant is defined as: where is Avogadro number and is charge of electron.

Step 1: Nature of constants.
Both and are universal constants.

Step 2: Conclusion.

Concept: Faraday’s laws of electrolysis.

Step 1: Hydrogen moles.


Step 2: Electrons required.


Step 3: Time doubled charge doubled.


Step 4: Silver deposition.

Concept: Hydrometallurgy involves extraction of metals using aqueous solutions, including displacement reactions.

Step 1: Understand the process.


Step 2: Identify process.
This type of displacement in aqueous solution is part of hydrometallurgy (cementation process). Conclusion:
Correct answer is hydrometallurgy.

Concept:

Step 1: Identify electrodes from given reaction.


Step 2: Use standard reduction potentials.


Step 3: Calculate EMF.
Conclusion:
Since EMF is negative, the given reaction is non-spontaneous.

Concept: Energy required:

Step 1: Convert heat.


Step 2: Charge required.


Step 3: Voltage.

Concept: Using Kohlrausch's law of independent migration of ions:

Step 1: Write expressions for given electrolytes.


Step 2: Eliminate .


Step 3: Find .
From: Adding:

Concept: Electrode potentials follow relations similar to Hess’s law: (Signs depend on direction of reactions.)

Step 1: Given values

Step 2: Apply correct relation From the diagram, the correct combination gives:

Step 3: Final adjustment Considering proper direction/sign convention from diagram: Conclusion

Concept: The relationship between Gibbs free energy, cell potential, and equilibrium constant is: Equating: At , this simplifies to:

Step 1: Number of electrons transferred:

Step 2: Calculate :

Step 3: Calculate : Final: