Electrochemistry Revision NCERT Class 12 Chemistry

 

💯 Electrochemistry Revision Q&A (NCERT Class 12 Chemistry)

Q. No.	Question	Answer
1	Define Electrochemistry.	The study of the relationship between chemical energy and electrical energy.
2	What is an electrochemical cell?	A device that converts chemical energy into electrical energy or vice-versa.
3	What is a Galvanic (or Voltaic) cell?	A cell where a spontaneous redox reaction generates electrical energy.
4	What is an Electrolytic cell?	A cell where electrical energy is used to drive a non-spontaneous chemical reaction.
5	What is the sign of the anode in a Galvanic cell?	Negative (site of oxidation).
6	What is the sign of the anode in an Electrolytic cell?	Positive (site of oxidation).
7	What is the function of a salt bridge?	To complete the inner circuit and maintain the electrical neutrality of the solutions.
8	Define EMF of a cell.	The maximum potential difference between two electrodes when no current is drawn.
9	Write the relation between ΔrG° and E°cell.	ΔrG° = -nFE°cell.
10	What is the unit of conductance (G)?	Siemens (S) or ohm-1.
11	What is the unit of conductivity (κ)?	Siemens per meter (S m-1) or S cm-1.
12	Define cell constant (G*).	The ratio of distance between electrodes (l) to the area of cross-section (A). (G* = l/A).
13	How does conductivity of an electrolyte vary with dilution?	It decreases (due to fewer ions per unit volume).
14	How does molar conductivity (Λm) of a strong electrolyte vary with dilution?	It increases slightly (due to decreased inter-ionic attraction).
15	State Kohlrausch's Law.	At infinite dilution, each ion contributes independently to the total molar conductivity.
16	How is the degree of dissociation (α) calculated for a weak electrolyte?	α = Λm / Λm°.
17	Write the simplified Nernst equation at 298 K.	Ecell = E°cell - (0.0591/n) log Q.
18	What is the value of Ecell at equilibrium?	Zero (Ecell = 0).
19	Write the relation between E°cell and the equilibrium constant (Kc).	E°cell = (0.0591/n) log Kc (at 298 K).
20	State Faraday's First Law of Electrolysis.	Mass deposited is directly proportional to the quantity of electricity passed (W ∝ Q).
21	What is the value of Faraday constant (F)?	96487 C mol-1.
22	How many moles of electrons are required to deposit 1 mol of Ca from Ca2+?	2 moles of electrons (2F).
23	Define Primary Battery.	A battery that cannot be recharged once the chemicals are exhausted.
24	Give an example of a primary battery.	Dry cell (Leclanché cell) or Mercury cell.
25	Define Secondary Battery.	A battery that can be recharged by passing current in the reverse direction.
26	Give an example of a secondary battery.	Lead storage battery or Nickel-Cadmium cell.
27	What is the overall cell reaction in a Mercury cell?	Zn(Hg) + HgO(s) → ZnO(s) + Hg(l).
28	Why is the voltage of a mercury cell constant throughout its life?	Because the overall reaction does not involve any ion whose concentration changes.
29	What is the electrolyte in a lead storage battery?	38% solution of H2SO4.
30	What is the material of the anode in a fully discharged lead storage battery?	Lead sulphate (PbSO4).
31	Define a Fuel cell.	A Galvanic cell that converts the energy of combustion of fuels directly into electrical energy.
32	Give an example of a fuel cell.	H2-O2 Fuel Cell.
33	What is the by-product of an H2-O2 fuel cell?	Water (H2O).
34	What is Corrosion?	The slow decay of a metal due to its reaction with air and moisture (an electrochemical process).
35	Write the chemical formula of rust.	Fe2O3·xH2O (Hydrated ferric oxide).
36	What is Galvanisation?	Coating iron with a layer of Zinc to prevent rusting.
37	Name the electrode whose standard potential is conventionally taken as zero.	Standard Hydrogen Electrode (SHE).
38	What is the cell reaction at the anode during the discharge of a dry cell?	Zn(s) → Zn2+ + 2e-.
39	What happens to ΔrG when Ecell is positive?	ΔrG is negative (spontaneous).
40	What is the condition for a non-spontaneous cell reaction?	Ecell is negative (or ΔrG is positive).
41	Why is the corrosion of iron quicker in saline water?	Salt acts as an electrolyte, increasing the conductivity and rate of the electrochemical process.
42	Why does Λm of weak electrolytes increase steeply on dilution?	Due to the increase in the degree of dissociation (α).
43	Which metal is a stronger reducing agent, A (E° = -2.5 V) or B (E° = -1.0 V)?	Metal A (more negative E°).
44	How is the potential of a single electrode measured?	By connecting it to the SHE to form a complete cell.
45	What is the minimum voltage required for the electrolysis of water?	E°cell ≈ -1.23 V.
46	What is the relationship between resistance (R) and cell constant (G*)?	κ = G*/R.
47	What is the unit of the cell constant (G*) in SI units?	m-1.
48	What does Λm° represent?	Limiting molar conductivity (molar conductivity at infinite dilution).
49	Give the SI unit of Λm.	S m2 mol-1.
50	What is the role of ZnCl2 in a dry cell?	It forms a complex with NH3 to prevent pressure build-up.
51	State Faraday's Second Law in terms of equivalent mass (E).	Mass deposited (W) is proportional to equivalent mass (W ∝ E) for the same Q.
52	What is the charge required for the reduction of 1 mol of MnO4- to Mn2+?	5 Faradays (5F).
53	What is the formula to calculate the mass deposited (W)?	W = ZIT, where Z is the electrochemical equivalent.
54	What is electrochemical equivalent (Z)?	The mass of the substance deposited by 1 C of charge (Z = E/F).
55	What is the anode in the H2-O2 fuel cell?	Porous carbon rod through which H2 gas is passed.
56	What is the electrolyte in the H2-O2 fuel cell?	Hot aqueous KOH or NaOH.
57	What metal is used for sacrificial protection of iron?	Zinc (Zn).
58	Name a noble metal used as an electrode in SHE.	Platinum (Pt).
59	What is the standard concentration for ions in E°?	1 M (Molar).
60	What is the standard pressure for gases in E°?	1 bar (or 1 atm).
61	What does the notation Zn | Zn2+ represent?	A half-cell of zinc metal dipped in Zn2+ solution.
62	What does the double vertical line (||) represent in cell notation?	A salt bridge or porous partition separating two half-cells.
63	Write the cell notation for the Daniell cell.	Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s).
64	Give one reason why Li is the strongest reducing agent in aqueous solution.	Extremely high hydration energy of the Li+ ion.
65	What is the condition for Ecell > 0?	ΔrG < 0 and Kc > 1.
66	What happens to the pH near the cathode during the electrolysis of aqueous NaCl?	It increases (becomes basic due to OH- formation).
67	What is the primary product at the anode during the electrolysis of aqueous NaCl?	Cl2 gas.
68	What is the primary product at the cathode during the electrolysis of aqueous NaCl?	H2 gas.
69	What does the term electrolysis of brine refer to?	Electrolysis of concentrated aqueous NaCl solution.
70	What happens to the concentration of H2SO4 during the recharging of a lead storage battery?	It increases.
71	What is the general term for the current-carrying ability of a metallic wire?	Metallic (or Electronic) Conductance.
72	How is Λm related to C (concentration) for a strong electrolyte? (Debye-Hückel-Onsager equation)	Λm = Λm° - A√C.
73	Why does the molar conductivity of strong electrolytes not increase sharply on dilution?	They are already completely dissociated at all concentrations.
74	What is the role of the Pt electrode in SHE?	It provides a surface for the reaction and for the transfer of electrons.
75	What is the major disadvantage of a dry cell?	It is an acidic cell, which corrodes the Zn casing.
76	What determines the extent of electronic conductance in a metal?	The number of valence electrons per atom.
77	How does temperature affect electronic conductance?	It decreases with an increase in temperature.
78	Give one example of a weak electrolyte.	CH3COOH (Acetic acid).
79	Give one example of a strong electrolyte.	NaCl (Sodium chloride).
80	Which process is faster: rusting in moist air or rusting in saltwater?	Rusting in saltwater (due to higher electrolyte content).
81	Write the cell reaction for the charging of a lead storage battery.	2PbSO4(s) + 2H2O(l) → Pb(s) + PbO2(s) + 2H2SO4(aq).
82	What is the approximate voltage of a single lead storage cell?	2 V (A typical car battery has 6 cells for 12 V).
83	What is the maximum work obtained from a Galvanic cell?	The decrease in Gibbs free energy (ΔrG).
84	Define electrochemical series.	The arrangement of various half-cells in order of their increasing standard reduction potentials.
85	What is the property of elements that have a high negative E°?	They are strong reducing agents.
86	What is the property of elements that have a high positive E°?	They are strong oxidizing agents.
87	Can you store AgNO3 solution in a Cu vessel? (E°Ag+/Ag > E°Cu2+/Cu)	No, Cu will spontaneously displace Ag (positive Ecell).
88	What is the role of a solid electrolyte in a fuel cell?	To facilitate the migration of ions between the electrodes.
89	What is the electrode material of the cathode in a dry cell?	Carbon rod (C) surrounded by MnO2 and carbon powder.
90	What is the reaction quotient (Q)?	The ratio of product concentrations to reactant concentrations raised to their stoichiometric powers, at any point.
91	At what temperature is the simplified Nernst equation (with 0.0591) valid?	298 K (or 25 °C).
92	Name the force that drives electrons in the external circuit.	Electromotive Force (EMF).
93	Which electrode is the site of Cl2 evolution during the electrolysis of molten NaCl?	Anode (Cl- → ½Cl2 + e-).
94	What is the common name for the reaction Fe2+ → Fe3+ + e-?	Oxidation of ferrous to ferric ion.
95	Why are strong electrolytes like KCl used in salt bridges?	Because the mobility of the cation (K+) and anion (Cl-) are nearly the same.
96	If ΔrG° = 0, what is the value of E°cell?	Zero (E°cell = 0).
97	How much electricity is needed to obtain 1 mol of Al from Al2O3 by electrolysis?	3 Faradays (3F).
98	Define Concentration Cell.	A Galvanic cell in which the two half-cells have the same electrodes but different concentrations of the electrolyte.
99	What technique is used to prevent corrosion by connecting the metal to a more easily oxidizable metal?	Cathodic protection (or Sacrificial protection).
100	What is the term for the decrease in EMF due to the formation of gas bubbles around the electrode?	Polarization.