The standard reduction potential of H⁺/H₂ electrode is taken as 0.00 V because:
Answer: B
SHE (Standard Hydrogen Electrode) is the arbitrary reference against which all other reduction potentials are measured.
Q.382Medium
During the electrolysis of aqueous CuSO₄ solution with copper electrodes, which reaction occurs at the cathode?
Answer: B
At cathode with copper electrodes in CuSO₄: Cu²⁺ ions are preferentially reduced as their reduction potential (+0.34 V) is higher than H⁺ (-0.83 V).
Q.383Medium
The Gibbs free energy change for an electrochemical cell reaction is related to cell potential by:
Answer: B
The standard free energy change ΔG° = -nFE°cell, where n is moles of electrons, F is Faraday constant, and E° is standard cell potential.
Q.384Medium
In the electrorefining of copper, impure copper acts as:
Answer: B
In electrorefining, impure copper acts as anode and undergoes oxidation. Pure copper deposits at cathode. More reactive impurities go into solution.
Q.385Easy
What is the effect of temperature on the conductivity of ionic solutions?
Answer: B
Conductivity increases with temperature because ionic mobility increases due to decreased viscosity of the medium.
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Q.386Easy
The electrochemical series is based on which property?
Answer: B
The electrochemical series arranges elements in order of their standard reduction potentials, with more positive values indicating stronger oxidizing agents.
Q.387Medium
In the electrolysis of dilute H₂SO₄ with inert electrodes, if 2 moles of electrons flow, what volume of gases (in liters at STP) will be produced?
Answer: A
At cathode: 2H⁺ + 2e⁻ → H₂ (1 mol H₂). At anode: 2H₂O → O₂ + 4H⁺ + 4e⁻ (0.5 mol O₂). With 2 mol e⁻: 1 mol H₂ (11.2 L) and 0.5 mol O₂ (5.6 L).
Q.388Medium
The cell potential of a galvanic cell decreases during operation because:
Answer: B
As the reaction proceeds, product concentrations increase while reactant concentrations decrease, reducing the driving force according to Nernst equation: E = E° - (0.059/n)log(Q).
Q.389Easy
Which factor does NOT significantly affect the conductance of an electrolytic solution?
Answer: C
Color of a solution is a physical property unrelated to ionic conductance. Conductance depends on nature of solute, concentration, temperature, and solvent.
Q.390Medium
For the reaction: Fe³⁺ + e⁻ → Fe²⁺ (E° = +0.77 V) and Cl₂ + 2e⁻ → 2Cl⁻ (E° = +1.36 V), which is the strongest oxidizing agent?
Answer: C
The species with highest reduction potential (+1.36 V) is Cl₂, making it the strongest oxidizing agent. Higher E° values indicate greater tendency to accept electrons.
Q.391Hard
The molar conductivity of a strong electrolyte at infinite dilution (Λ°m) can be calculated using Kohlrausch's law. For NaCl, if Λ°m(HCl) = 426, Λ°m(NaOH) = 248, and Λ°m(KCl) = 150, then Λ°m(NaCl) is:
During the electrolysis of molten NaCl using inert electrodes, if 2.3 g of Na is deposited at the cathode, what volume of Cl₂ gas (at STP) will be released at the anode?
Answer: B
At cathode: Na⁺ + e⁻ → Na; moles of Na = 2.233 = 0.1 mol. At anode: 2Cl⁻ → Cl₂ + 2e⁻; for 0.1 mol Na, electrons = 0.1 mol, so Cl₂ moles = 0.21 = 0.05 mol. Volume at STP = 0.05 × 22.4 = 1.12 L.
Q.393Medium
A galvanic cell is constructed using Zn|Zn²⁺ and Cu|Cu²⁺ half-cells. If the concentration of Zn²⁺ is increased from 1 M to 10 M at 25°C, how does this affect the cell potential? (E°cell = 1.1 V)
Answer: A
Using Nernst equation: Ecell = E°cell - (0.059/n)log(Q). Increasing [Zn²⁺] increases Q, making the log term positive, which decreases Ecell. ΔE = -(0.2059)log(10) = -0.0295 ≈ -0.0296 V.
Q.394Easy
The rate of a chemical reaction is defined as the change in concentration of reactants or products per unit time. Which of the following is NOT a factor affecting reaction rate?
Answer: C
The color of the reaction vessel does not affect the reaction rate. Temperature, nature of reactants, concentration, pressure, and catalyst are actual factors affecting reaction rate.
Q.395Easy
The half-life of a zero-order reaction is:
Answer: B
For a zero-order reaction, t₁/₂ = [A]₀/(2k), which is directly proportional to initial concentration.
Q.396Easy
A reaction has a rate constant of k = 2.5 × 10⁻⁴ s⁻¹ at 298 K. What is the order of this reaction if the units of k are s⁻¹?
Answer: B
The units s⁻¹ or time⁻¹ indicate a first-order reaction. For first-order reactions, the rate constant has units of time⁻¹.
Q.397Easy
Which of the following statements about activation energy (Eₐ) is correct?
Answer: C
Activation energy is the minimum energy required for reactants to overcome the energy barrier and form products. It is always positive and independent of temperature.
Q.398Medium
For a first-order reaction, if the initial concentration is [A]₀ = 0.5 M and after 30 seconds it becomes 0.25 M, what is the rate constant?
Answer: A
Using ln([A]₀/[A]ₜ) = kt, ln(0.05.25) = k × 30, ln(2) = k × 30, k = 0.30693 = 0.0231 s⁻¹
Q.399Medium
The mechanism of a reaction is: Step 1: A + B → C (slow), Step 2: C + D → E + F (fast). What is the overall reaction and the rate law?
Answer: A
The overall reaction is obtained by adding all steps and canceling intermediates: A + B + D → E + F. Rate law is determined by the slow step: rate = k[A][B]
Q.400Medium
Which of the following graphs represents a first-order reaction?
Answer: B
For a first-order reaction, ln[A] = ln[A]₀ - kt, so a plot of ln[A] vs t gives a straight line with slope -k.
