Electrochemistry-Assertion & Reason Type Question & Answers Class 12 Chemistry Worksheet
Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as:
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If both assertion and reason are false
1. Assertion: The rusting of iron, tarnishing of silver, development of green coating on copper and bronze are some of the examples of corrosion.
Reason: It causes enormous damage to buildings, bridges, ships and to all objects made of metals especially that of iron.
2. Assertion: Molar conductivity increases with decrease in concentration of solution.
Reason: Conductivity always decreases with decrease in concentration of solution.
3. Assertion: Zinc can be used while copper cannot be used in the recovery of Ag from the complex [Ag(CN)2 ] – .
Reason: Zinc is a powerful reducing agent than copper.
4. Assertion: The resistivity for a substance is its resistance when it is one-meter-long and its area of cross section is one square meter.
Reason: The SI units of resistivity is ohm metre (Ωm).
5. Assertion: On increasing dilution, the specific conductance keeps on increasing.
Reason: On increasing dilution, degree of ionisation of weak electrolyte increases and molality of ions also increases.
6. Assertion: The conductivity of electrolytic solutions increases with increase of temperature.
Reason: Electronic conductance of metals decreases with increase of temperature.
7. Assertion: During electrolysis of CuSO4 (aq) using copper electrodes, copper is dissolved at anode and deposited at cathode.
Reason: Oxidation takes place at anode and reduction at cathode.
8. Assertion: To obtain maximum work from a galvanic cell charge has to be passed reversibly.
Reason: The reversible work done by a galvanic cell is equal to decrease in its Gibbs energy.
9. Assertion: Conductivity of an electrolyte increases with decrease in concentration.
Reason: Number of ions per unit volume decreases on dilution.
10. Assertion: In cell, current stops flowing when Ecell = 0.
Reason: Equilibrium of the cell reaction is attained.
Answers –
1. (a)
Corrosion is usually defined as the degradation of metals due to an electrochemical process. The formation of rust on iron, tarnish on silver, and the blue-green patina that develops on copper and bronze are all examples of corrosion. Rust is hydrated ferric oxide Fe2O3.H2O. It causes enormous damage to buildings, bridges, ships and to all objects made of metals especially that of iron. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
2. (b)
Conductivity always decreases with a decrease in concentration whereas, molar conductivity increase with dilution. This is because the conductivity of a solution is the conductance of one-unit volume of the solution, but molar conductivity is the conductance of that volume of solution containing one mole of an electrolyte. Thus, both assertion and reason are correct but reason is not the correct explanation of assertion.
3. (a)
Zinc is used in the recovery of Ag from the complex [Ag(CN)2]– whereas copper is not used because zinc is more powerful reducing agent than copper. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
4. (b)
We know that: R ∝ l / A or R = ρ (l/ A) Where, l = length of substance A = area of cross-section ρ = proportionality constant is called resistivity. If l = 1 m and A = 1 m2 Then, R = ρ i.e., resistance = Resistivity. The SI units of resistivity is ohm metre (Ωm). Thus, both assertion and reason are true but reason is not the correct explanation of the assertion.
5. (b)
On increasing dilution specific conductance increases because it is directly proportional to dilution. When more amount of solvent such as water is added to the solution, it results in dissociating the molecules into ions of a weak electrolyte. Thus, the degree of ionisation of weak electrolyte increases upon dilution. The mobility of ions will also increase because the ions will get the more free space to move. Thus, both assertion and reason are correct but reason is not the correct explanation of assertion.
6. (b)
As the temperature increases the electrolytic conductivity of solutions increases because with increase in the temperature ionisation increases and the mobility of ions also increases. In metals, conductivity is due to movement of free electrons. When we increase the temperature the vibrational motion of electrons increases which causes unwanted collisions which results in the increase of resistance in metals. Therefore, the mobility of electrons decreases and causes decrease in conductivity. Thus, both assertion and reason are correct but reason is not the correct explanation of assertion. At cathode: Cu+2 (aq) + 2e– → Cu(s) (Reduction) At anode: Cu(s) → Cu+2 (aq) + 2e– (Oxidation)
7. (a)
From the above redox reactions, it is clear that during the electrolysis of CuSO4 (aq) using copper electrodes, copper is dissolved at anode and deposited at cathode. Also, oxidation takes place at anode and reduction at cathode. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
8. (a)
To obtain maximum work from a galvanic cell charge has to be passed reversibly because electrical work done in one second is equal to the electrical potential multiplies by total charge. The reversible work done by a galvanic cell is equal to the decrease in its Gibbs energy. Therefore, if nF is the amount of charge passed and E is the emf of the cell and DG is the Gibbs energy of reaction then, ΔG = – nFEcell Hence, both Assertion and reason are correct and also reason is the correct explanation for Assertion.
9. (a)
For both strong and weak electrolyte, conductivity always decreases with the decrease in concentration. This is because the number of ions per unit volume that carry the current in a solution decreases on dilution. Thus, both assertion and reason are true and reason is the correct explanation of assertion.
10. (a)
For reaction to be spontaneous, Ecell should have a positive value and Δr Gcell negative. Hence, Current stops flowing when Ecell = 0 because equilibrium of the cell reaction is attained. Thus, both assertion and reason are true and reason is the correct explanation of assertion.