CBSE Class 12th Chemistry Chapter 2 - Electrochemistry Important Questions with Answers

(a) The cell in which the following reaction occurs:
2Fe³⁺ (aq) + 2I^–(aq) ? 2Fe²⁺ (aq) + I₂(s)
has \(\mathbf{E}_{\text { Cell }}^{\mathrm{o}}\) = 0.236 V at 298 K. Calculate the standard Gibbs energy of the cell reaction. (Given: 1F = 96,500 C mol^-1)
(b) How many electrons flow through a metallic wire if a current of 0.5 A is passed for 2 hours? (Given: 1F = 96,500 C mol^-1) (All India 2017)

Why an electrochemical cell stop working after some time? The reduction potential of an electrode depends upon the concentration of solution with which it is in contact. (All India 2017)

Calculate ?_rG° and log K_c for the following reaction at 298 K.
\(2 \mathrm{Cr}_{(\mathrm{s})}+3 \mathrm{Cd}_{(\mathrm{aq})}^{2+} \longrightarrow 2 \mathrm{Cr}_{\mathrm{raq}}^{3+}+3 \mathrm{Cd}_{(\mathrm{s})}\)
[Given : \(\mathbf{E}_{\mathrm{Cell}}^{\mathbf{0}}\) = +0.34 V, IF = 96500 C mol^-1] (Comptt. All India 2017)

Calculate ?_rG° and log K. for the following reaction at 298 K. (Comptt. All India 2017)

(a) When a bright silver object is placed in the solution of gold chloride, it acquires a golden tinge but nothing happens when it is placed in a solution of copper chloride. Explain this behaviour of silver.
[Given : \(\mathbf{E}_{\mathrm{Cu}^{2+} / \mathrm{Cu}}^{0}\) =+0.34V,\(\mathbf{E}_{\mathbf{A} \mathbf{g}^{+} / \mathbf{A g}}^{\mathbf{0}}\) =+0.80V, \(\mathrm{E}_{\mathrm{Au}^{3+} / \mathrm{Au}}^{0}\) = +1.40V]
(b) Consider the figure given and answer the following questions :
(i) What is the direction of flow of electrons?
(ii) Which is anode and which is cathode?
(iii) What will happen if the salt bridge is removed?

(iv) How will concentration of Zn2+ and Ag+ ions be affected when the cell functions?
(v) How will concentration of these ions be affected when the cell becomes dead? (Comptt. Delhi 2017)

(a) What is limiting molar conductivity? Why there is steep rise in the molar conductivity of weak electrolyte on dilution?
(b) Calculate the emf of the following cell at 298 K :
Mg (s) | Mg²⁺ (0.1 M) || Cu²⁺ (1.0 × 10^-3M) | Cu (s)
[Given = \(\mathbf{E}_{\text { Cell }}^{0}\) = 2.71 V]. (Comptt. Delhi 2017)

Calculate e.m.f. of the following cell at 298 K: 2Cr(s) + 3Fe²⁺ (0.1 M) ? 2Cr³⁺ (0.01 M) + 3 Fe(s)
Given: E⁰(Cr³⁺| Cr) = -0.74 V E⁰(Fe²⁺ | Fe) = -0.44 V (Delhi 2016)

(a) Calculate E⁰_cell for the following reaction at 298 K:
2Al(s) + 3Cu²⁺ (0.01M) ? 2Al²⁺ (0.01M) + 3Cu(s)
Given: E_cell = 1.98 V
(b) Using the E⁰ values of A and B, predict which is better for coating the surface of iron [E⁰(Fe²⁺/Fe) = -0.44 V] to prevent corrosion and why?
Given: E⁰(A²⁺/A) = -2.37 V; E⁰(B²⁺/B) = -0.14 V (All India 2016)

(a) The conductivity of 0.001 mol L^-1 solution of CH₃COOH is 3.905 × 10^-5 S cm^-1. Calculate its molar conductivity and degree of dissociation (?).
Given: ?⁰(H⁺) = 349.6 S cm² mol^-1 and ?⁰ (CH₃COO^–) = 40.9 S cm² mol^-1
(b) Define electrochemical cell. What happens if external potential applied becomes greater than E⁰_cell of electrochemical cell? (All India 2016)

(a) What are the two classifications of batteries? What is the difference between them?
(b) The resistance of 0.01 M NaCl solution at 25°C is 200 ?. The cell constant of the conductivity cell is unity. Calculate the molar conductivity of the solution. (Comptt. All India 2016)