List of top Chemistry Questions on Electrochemistry asked in CBSE CLASS XII

Batteries and fuel cells are very useful forms of galvanic cells. Any battery or cell that we use as a source of electrical energy is basically a galvanic cell. However, for a battery to be of practical use, it should be reasonably light, compact, and its voltage should not vary appreciably during its use. There are mainly two types of batteries — primary batteries and secondary batteries.
In primary batteries, the reaction occurs only once and after use over a period of time, the battery becomes dead and cannot be reused again, whereas the secondary batteries are rechargeable.
Production of electricity by thermal plants is not a very efficient method and is a major source of pollution. To solve this problem, galvanic cells are designed in such a way that energy of combustion of fuels is directly converted into electrical energy, and these are known as fuel cells. One such fuel cell was used in the Apollo space program.
Answer the following questions:

Compound (A) \( \left( \text{C}_6\text{H}_{12}\text{O}_2 \right) \) on reduction with LiAlH4 gives two compounds (B) and (C). The compound (B) on oxidation with PCC gives compound (D) which upon treatment with dilute NaOH and subsequent heating gives compound (E). Compound (E) on catalytic hydrogenation gives compound (C). The compound (D) is oxidized further to give compound (F) which is found to be a monobasic acid (Molecular weight = 60). Identify the compounds (A), (B), (C), (D), (E) and (F).}

Complete and balance the following chemical equations: \( 3 \text{MnO}_4^- + 4 \text{H}^+ \longrightarrow ? \)
\( \text{Cr}_2 \text{O}_7^{2-} + 14 \text{H}^+ + 6 \text{Fe}^{2+} \longrightarrow ? \)

Calculate the \( \Delta G^\circ \) and \( \log K_c \) for the following cell reaction:
\(\text{Fe (s)} + \text{Ag}^+ (aq) \rightleftharpoons \text{Fe}^{2+} (aq) + \text{Ag (s)}\)
Given: \( E^\circ_{\text{Fe}^{2+}/\text{Fe}} = -0.44 \, \text{V}, E^\circ_{\text{Ag}^+/ \text{Ag}} = +0.80 \, \text{V} \)
\( 1 F = 96500 \, \text{C mol}^{-1} \)

State Faraday's second law of electrolysis. How will the pH of aqueous NaCl solution be affected when it is electrolyzed?

Write any two advantages of fuel cells over primary and secondary batteries?

How many Faradays are required for the oxidation of one mole of \( \text{H}_2\text{O} \) to \( \text{O}_2 \)?

Calculate emf of the following cell at 25°C:
\(\text{Zn (s)} | \text{Zn}^{2+} (0.001M) || \text{Cd}^{2+} (0.1M) | \text{Cd (s)}\) Given: \( E^\circ_{\text{Zn}^{2+}/\text{Zn}} = -0.76 \, \text{V}, E^\circ_{\text{Cd}^{2+}/\text{Cd}} = -0.40 \, \text{V} \)
\([ \log 10 = 1 ]\)

Arrange the following in decreasing order of their acidic strength:
\( \text{CH}_3\text{COOH}, \, \text{O}_2\text{N}-\text{CH}_2\text{COOH}, \, \text{HCOOH} \)

The conductivity of a 0.2 M solution of KCl is \( 2.48 \times 10^{-2} \) S cm\(^{-1}\). Calculate its molar conductivity and degree of dissociation (\( \alpha \)).
Given: \( \lambda^0_{\text{K}^+} = 73.5 \, \text{S cm}^2 \text{mol}^{-1} \), \( \lambda^0_{\text{Cl}^-} = 76.5 \, \text{S cm}^2 \text{mol}^{-1} \)

The conductivity of sodium chloride at 298 K has been determined at different concentrations and the results are given below: 
Concentration/M 0.001 0.010 0.020 0.050 0.100 
10²  × κ/S m^-1  1.237 11.85 23.15 55.53 106.74 
Calculate \(\land_m\) for all concentrations and draw a plot between \(\land_m\) and c ½. Find the value of  \(\land^0_m\).

Write the Nernst equation and emf of the following cells at 298 K : 
(i) Mg(s) | Mg²⁺ (0.001M) || Cu²⁺(0.0001 M) | Cu(s) 
(ii) Fe(s) | Fe²⁺ (0.001M) || H⁺ (1M)|H₂(g)(1bar) | Pt(s) 
(iii) Sn(s) | Sn²⁺(0.050 M) || H⁺ (0.020 M) | H₂(g) (1 bar) | Pt(s) 
(iv) Pt(s) | Br₂(l) | Br^-  (0.010 M) || H⁺ (0.030 M) | H₂(g) (1 bar) | Pt(s).

Using the standard electrode potentials given in Table 3.1, predict if the reaction between the following is feasible: 
(i) Fe³⁺ (aq) and I^- (aq) 
(ii) Ag⁺ (aq) and Cu(s) 
(iii) Fe³⁺(aq) and Br^-(aq) 
(iv) Ag(s) and Fe³⁺(aq) 
(v) Br₂ (aq) and Fe²⁺(aq).

Depict the galvanic cell in which the reaction Zn(s) + 2Ag⁺(aq) → Zn²⁺(aq) + 2Ag(s) takes place. Further show: 
 (i) Which of the electrode is negatively charged? 
 (ii) The carriers of the current in the cell. 
 (iii) Individual reaction at each electrode.

A solution of Ni(NO₃)₂ is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?

How much charge is required for the following reductions: 
  (i) 1 mol of Al³⁺  to Al. 
  (ii) 1 mol of Cu²⁺ to Cu. 
  (iii) 1 mol of MnO^-₄ to Mn²⁺ .

In the button cells widely used in watches and other devices the following reaction takes place:
Zn(s) + Ag₂O(s) + H₂O(l) \(\rightarrow\) Zn²⁺_(aq) + 2Ag(s) + 2OH^-  (aq) 
Determine \(\triangle _rG^\ominus\) and \(E^\ominus\) for the reaction.

Predict the products of electrolysis in each of the following: 
 (i) An aqueous solution of AgNO₃ with silver electrodes. 
 (ii) An aqueous solution of AgNO₃ with platinum electrodes. 
 (iii) A dilute solution of H₂SO₄ with platinum electrodes. 
 (iv) An aqueous solution of CuCl₂ with platinum electrodes.

How much electricity is required in coulomb for the oxidation of 
(i) 1 mol of H₂O to O₂. 
(ii) 1 mol of FeO to Fe₂O₃.

Conductivity of 0.00241 M acetic acid is 7.896 × 10^-5 S cm^-1 . Calculate its molar conductivity and if \(\land^0_m\) for acetic acid is 390.5 S cm² mol^-1 , what is its dissociation constant?

The resistance of a conductivity cell containing 0.001M KCl solution at 298 K is 1500 Ω. What is the cell constant if conductivity of 0.001M KCl solution at 298 K is 0.146 x 10^-3 S cm^-1 .