Chapter 3 Electrochemistry

Here’s the complete set of 50 Assertion and Reason Questions for Chapter 3: Electrochemistry, ensuring coverage of all key concepts.

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Assertion and Reason Questions for CBSE Class 12 Chemistry – Chapter 3: Electrochemistry

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Electrochemical Cells

1. Assertion (A): A galvanic cell always has a positive EMF.
   Reason (R): The cathode in a galvanic cell is the site of oxidation.
   Answer: 3
   Explanation: The cathode is the site of reduction, not oxidation. The EMF is positive for a spontaneous reaction.

2. Assertion (A): Standard EMF of a galvanic cell depends on the standard reduction potentials of electrodes.
   Reason (R): EMF is the difference between the reduction potentials of the cathode and the anode.
   Answer: 1
   Explanation: The EMF of a galvanic cell is calculated as $E^\circ_{cell} = E^\circ_{cathode} - E^\circ_{anode}$ .

3. Assertion (A): A salt bridge is required in an electrochemical cell.
   Reason (R): The salt bridge maintains the electrical neutrality of the system.
   Answer: 1
   Explanation: The salt bridge allows ion movement to prevent charge buildup in half-cells.

4. Assertion (A): In a galvanic cell, oxidation takes place at the anode.
   Reason (R): Electrons flow from the cathode to the anode.
   Answer: 3
   Explanation: Electrons flow from the anode to the cathode, where oxidation occurs at the anode.

5. Assertion (A): Zinc is used as the anode in a Daniell cell.
   Reason (R): Zinc has a more negative reduction potential than copper.
   Answer: 1
   Explanation: Zinc oxidizes (acts as the anode) due to its lower reduction potential compared to copper.

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Nernst Equation

6. Assertion (A): The Nernst equation relates the EMF of a cell to the concentrations of reactants and products.
   Reason (R): The Nernst equation incorporates the reaction quotient $Q$ .
   Answer: 1
   Explanation: The Nernst equation $E = E^\circ - \frac{RT}{nF} \ln Q$ connects EMF and reactant/product concentrations.

7. Assertion (A): The EMF of a cell is zero at equilibrium.
   Reason (R): At equilibrium, there is no net electron flow in the cell.
   Answer: 1
   Explanation: When the reaction reaches equilibrium, $Q = K_{eq}$ , making the EMF zero.

8. Assertion (A): Increasing the concentration of reactants in a galvanic cell increases its EMF.
   Reason (R): EMF depends on the reaction quotient $Q$ , which decreases with higher reactant concentration.
   Answer: 1
   Explanation: Higher reactant concentrations lower $Q$ , increasing $E$ (EMF).

9. Assertion (A): The Nernst equation applies only to galvanic cells.
   Reason (R): The equation assumes non-equilibrium conditions, which are specific to galvanic cells.
   Answer: 4
   Explanation: The Nernst equation applies to all electrochemical cells, including electrolytic cells.

10. Assertion (A): The standard reduction potential of an electrode is temperature-dependent.
    Reason (R): Standard reduction potential depends on thermodynamic parameters like enthalpy and entropy.
    Answer: 1
    Explanation: Temperature affects Gibbs free energy, influencing reduction potential.

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Faraday’s Laws of Electrolysis

11. Assertion (A): The amount of substance deposited during electrolysis is proportional to the quantity of electricity passed.
    Reason (R): Faraday’s first law of electrolysis states that mass deposited is proportional to charge.
    Answer: 1
    Explanation: Faraday’s first law confirms the proportionality of mass and charge.

12. Assertion (A): The same quantity of electricity deposits different masses of substances at different electrodes.
    Reason (R): Faraday’s second law of electrolysis considers equivalent weights of ions.
    Answer: 1
    Explanation: Mass depends on equivalent weight, as per Faraday’s second law.

13. Assertion (A): Electrolysis of molten NaCl produces sodium at the cathode.
    Reason (R): Sodium ions are reduced to sodium metal at the cathode.
    Answer: 1
    Explanation: At the cathode, $Na^+$ ions gain electrons, forming sodium metal.

14. Assertion (A): The products of electrolysis of an aqueous solution depend on the electrode potentials of ions.
    Reason (R): The more positive reduction potential ion is preferentially discharged.
    Answer: 1
    Explanation: Reduction potential determines which ion is reduced during electrolysis.

15. Assertion (A): Electrolysis of water is more efficient in acidic medium than neutral medium.
    Reason (R): Acidic medium provides $H^+$ ions that increase conductivity.
    Answer: 1
    Explanation: Higher ion concentration in acidic solutions enhances water electrolysis.

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Electrochemical Series

16. Assertion (A): Elements at the top of the electrochemical series are strong reducing agents.
    Reason (R): These elements have high negative standard reduction potentials.
    Answer: 1
    Explanation: High negative potentials indicate a greater tendency to lose electrons.

17. Assertion (A): Hydrogen is included in the electrochemical series with a potential of 0 V.
    Reason (R): It serves as the reference electrode for standard reduction potentials.
    Answer: 1
    Explanation: Hydrogen’s potential is arbitrarily set to zero as a reference.

18. Assertion (A): Metals like gold and platinum are corrosion-resistant.
    Reason (R): These metals have high reduction potentials.
    Answer: 1
    Explanation: High reduction potentials make gold and platinum less reactive.

19. Assertion (A): Sodium metal reacts vigorously with water.
    Reason (R): Sodium has a very negative standard reduction potential.
    Answer: 1
    Explanation: Sodium’s low reduction potential makes it highly reactive with water.

20. Assertion (A): Copper cannot displace hydrogen from acids.
    Reason (R): Copper has a positive standard reduction potential.
    Answer: 1
    Explanation: Positive potential indicates copper is less reactive than hydrogen.

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Corrosion

21. Assertion (A): Corrosion of metals is an electrochemical process.
    Reason (R): Corrosion involves oxidation at anodic sites and reduction at cathodic sites.
    Answer: 1
    Explanation: Corrosion occurs via electrochemical reactions, forming metal oxides.

22. Assertion (A): Galvanization prevents rusting of iron.
    Reason (R): Zinc acts as a sacrificial anode, protecting iron from oxidation.
    Answer: 1
    Explanation: Zinc corrodes preferentially, protecting the underlying iron.

23. Assertion (A): Rusting of iron is faster in saline water than pure water.
    Reason (R): Saline water increases the conductivity of the medium.
    Answer: 1
    Explanation: Higher ion concentration in saline water enhances electrochemical reactions.

24. Assertion (A): Paint prevents rusting of metals.
    Reason (R): Paint acts as a barrier, preventing contact with air and moisture.
    Answer: 1
    Explanation: A protective coating prevents environmental exposure, reducing rusting.

25. Assertion (A): Corrosion of aluminum is self-limiting.
    Reason (R): Aluminum forms a protective oxide layer that prevents further corrosion.
    Answer: 1
    Explanation: The aluminum oxide layer is stable and inhibits further oxidation.

Batteries

26. Assertion (A): A lead-acid battery is rechargeable.
    Reason (R): In a lead-acid battery, the discharge reaction is reversible.
    Answer: 1
    Explanation: The reaction between lead, lead dioxide, and sulfuric acid is reversible, making the battery rechargeable.

27. Assertion (A): In a dry cell, zinc acts as an anode.
    Reason (R): Zinc oxidizes to form $Zn^{2+}$ , releasing electrons.
    Answer: 1
    Explanation: The oxidation of zinc at the anode generates electrons, powering the cell.

28. Assertion (A): Lithium-ion batteries have a high energy density.
    Reason (R): Lithium is the lightest metal and has a high electrode potential.
    Answer: 1
    Explanation: Lithium’s properties enable lightweight and efficient batteries.

29. Assertion (A): Alkaline batteries have a longer shelf life than zinc-carbon batteries.
    Reason (R): Alkaline batteries use potassium hydroxide as the electrolyte.
    Answer: 1
    Explanation: The alkaline medium reduces corrosion, enhancing battery life.

30. Assertion (A): Nickel-cadmium batteries are used in portable electronic devices.
    Reason (R): Nickel-cadmium batteries are lightweight and rechargeable.
    Answer: 1
    Explanation: Rechargeable batteries with good energy density are ideal for portable devices.

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Fuel Cells

31. Assertion (A): Fuel cells are more efficient than conventional combustion engines.
    Reason (R): Fuel cells directly convert chemical energy into electrical energy.
    Answer: 1
    Explanation: Fuel cells bypass the thermodynamic limitations of heat engines.

32. Assertion (A): Hydrogen-oxygen fuel cells emit water as the only product.
    Reason (R): Hydrogen is oxidized and oxygen is reduced in a fuel cell.
    Answer: 1
    Explanation: The reaction $2H_2 + O_2 \rightarrow 2H_2O$ produces water.

33. Assertion (A): Methanol can be used as a fuel in fuel cells.
    Reason (R): Methanol is a liquid fuel that can be easily stored and transported.
    Answer: 1
    Explanation: Methanol is oxidized in fuel cells to generate electricity and heat.

34. Assertion (A): Fuel cells operate silently compared to conventional engines.
    Reason (R): Fuel cells have no moving parts during operation.
    Answer: 1
    Explanation: The electrochemical process in fuel cells eliminates mechanical noise.

35. Assertion (A): Alkaline fuel cells are commonly used in space missions.
    Reason (R): They provide a high power-to-weight ratio and emit pure water.
    Answer: 1
    Explanation: Alkaline fuel cells are efficient and provide potable water as a by-product.

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Industrial Applications

36. Assertion (A): Electrolysis is used for electroplating metals.
    Reason (R): Electroplating involves depositing a metal layer by reducing its ions.
    Answer: 1
    Explanation: Metal ions in the electrolyte are reduced and deposited on the substrate.

37. Assertion (A): Electrolysis of brine produces chlorine gas at the anode.
    Reason (R): Chloride ions are oxidized to chlorine gas at the anode.
    Answer: 1
    Explanation: In brine electrolysis, $Cl^-$ is oxidized to $Cl_2$ .

38. Assertion (A): Aluminum is extracted by the electrolysis of alumina.
    Reason (R): Alumina is dissolved in molten cryolite to reduce the melting point.
    Answer: 1
    Explanation: Cryolite acts as a flux, reducing the melting point of alumina for efficient electrolysis.

39. Assertion (A): Electrorefining is used to purify metals.
    Reason (R): Impure metal is used as an anode, and pure metal is deposited at the cathode.
    Answer: 1
    Explanation: Electrorefining ensures the deposition of pure metal at the cathode.

40. Assertion (A): In the chlor-alkali process, sodium hydroxide is obtained as a by-product.
    Reason (R): Sodium ions react with hydroxide ions in the cathodic compartment.
    Answer: 1
    Explanation: The process produces $NaOH$ , $Cl_2$ , and $H_2$ .

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Conductivity

41. Assertion (A): Conductivity decreases with dilution for strong electrolytes.
    Reason (R): The number of ions per unit volume decreases with dilution.
    Answer: 1
    Explanation: Dilution reduces ion concentration, lowering conductivity.

42. Assertion (A): Molar conductivity increases with dilution.
    Reason (R): The mobility of ions increases with decreasing concentration.
    Answer: 1
    Explanation: Molar conductivity accounts for ion movement, which improves with dilution.

43. Assertion (A): Weak electrolytes have lower conductivity than strong electrolytes at the same concentration.
    Reason (R): Weak electrolytes partially ionize in solution.
    Answer: 1
    Explanation: The extent of ionization affects the number of charge carriers.

44. Assertion (A): Kohlrausch’s law helps determine the molar conductivity of weak electrolytes.
    Reason (R): The law separates individual ion contributions to molar conductivity.
    Answer: 1
    Explanation: Kohlrausch’s law is used for extrapolating limiting molar conductivity.

45. Assertion (A): Conductivity of an electrolyte depends on the temperature.
    Reason (R): Increasing temperature enhances ion mobility.
    Answer: 1
    Explanation: Higher temperature reduces viscosity, improving ion movement.

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Miscellaneous

46. Assertion (A): Resistance of an electrolyte solution increases with dilution.
    Reason (R): Dilution increases the distance between the electrodes.
    Answer: 1
    Explanation: Increasing the distance decreases the availability of ions per unit volume.

47. Assertion (A): Electrolytes conduct electricity through the movement of ions.
    Reason (R): Electrons move freely in electrolytes.
    Answer: 3
    Explanation: Conductivity is due to ions, not electrons, in electrolytes.

48. Assertion (A): An increase in ion charge increases conductivity.
    Reason (R): Higher charges increase the movement of ions.
    Answer: 3
    Explanation: High charge can increase attraction, sometimes hindering ion mobility.

49. Assertion (A): Strong acids are good conductors of electricity.
    Reason (R): Strong acids ionize completely in aqueous solutions.
    Answer: 1
    Explanation: Complete ionization produces more charge carriers.

50. Assertion (A): Electrochemical cells are used in electroplating, electrorefining, and energy production.
    Reason (R): They convert chemical energy into electrical energy.
    Answer: 2
    Explanation: Only galvanic cells convert chemical to electrical energy; electrolytic cells do not.