Chemistry · Class 12 Science
Ch 7Electrochemistry — Class 12 Chemistry, concept-first.
Electrochemistry is the branch of chemistry concerned with the interconversion of chemical energy and electrical energy, and it rests entirely on the redox (reduction-oxidation) reactions already familiar from earlier study: reactions in which one species loses electrons (is oxidized) while another gains those same ele…
Key concepts
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Galvanic Cells
A galvanic cell (also called a voltaic cell) is a device that converts the chemical energy of a spontaneous redox reaction directly into electrical energy.
Most relevant Q&A
- A galvanic (voltaic) cell is set up by dipping a zinc rod into a $\text{ZnSO}_4$ solution and a copper rod into a $\text{CuSO}_4$ solution,…Free
- A galvanic cell is built by combining a silver electrode dipped in $1\ \text{M}\ \text{AgNO}_3$ with a copper electrode dipped in $1\ \text{…Free
- For the spontaneous reaction $\text{Zn}(s) + \text{Cu}^{2+}(aq) \to \text{Zn}^{2+}(aq) + \text{Cu}(s)$ that drives a Daniell cell, identify…Free
In previous exams
How often this chapter’s concepts have been examined — real appearance data, never estimated.
Chapter contents
The NCERT structure, section by section. Open a section to see its questions, then read the concept-first solution.
Redox Reactions Revisited: The Basis of Electrochemistry
Electrochemistry is the branch of chemistry concerned with the interconversion of chemical energy and electrical energy, and it rests entirely on the redox (reduction-oxidation) reactions already fami…
Electrochemical Cells: Galvanic Cells and Electrolytic Cells
An electrochemical cell is any device in which a redox reaction is coupled to the flow of electric current through an external circuit.
Construction and Working of the Daniell Cell
The Daniell cell, named after the English chemist John Frederic Daniell, is built from two half-cells: a zinc rod dipped in a solution, and a copper rod dipped in a solution.
Cell Representation (Cell Notation)
Describing a galvanic cell fully — the electrode materials, which one is oxidized and which is reduced, and the concentrations involved — normally takes several sentences or a diagram.
Electrode Potential and Standard Electrode Potential
Every metal electrode dipped into a solution of its own ions develops a characteristic electrical potential, arising from the competing tendencies of metal atoms to lose electrons and enter solution a…
The Standard Hydrogen Electrode
The standard hydrogen electrode (SHE) is the universally agreed reference point against which every other electrode's standard potential is measured, chosen by international convention to have a stand…
Standard EMF of a Cell from Standard Electrode Potentials
With every electrode's standard reduction potential tabulated against the common SHE reference, the standard EMF of any galvanic cell formed from any two of those electrodes can be predicted directly,…
Nernst Equation and the Equilibrium Constant of a Cell Reaction
Standard electrode potentials and the standard cell EMF, , are only strictly valid under the defined standard conditions — every solute at exactly , any gas at exactly , and the temperature at .
Gibbs Energy Change and Cell EMF
A spontaneous chemical reaction can, in principle, be harnessed to do useful work, and the maximum non-expansion (e.g.
Conductance of Electrolytic Solutions: Specific Conductivity
An electrolyte solution, like a metal wire, resists the flow of electric current to some degree, and this resistance, , can be measured by placing two fixed electrodes in the solution (forming a condu…
Molar Conductivity and Its Variation with Concentration
Specific conductivity, , describes how well a given volume of solution conducts, but it mixes together two separate effects: how many ions are actually present, and how well each individual ion conduc…
Kohlrausch's Law of Independent Migration of Ions
Because a weak electrolyte's cannot be found by extrapolating its own concentration-dependent data, Kohlrausch's law of independent migration of ions provides the indirect route needed to obtain it, u…
Electrolysis and Faraday's Laws of Electrolysis
Electrolysis is the process of using an externally supplied electric current to drive a non-spontaneous redox reaction — the reverse of what a galvanic cell does.
Batteries: Primary Cells, Fuel Cells and the Li-ion Battery
Batteries take the principle of the galvanic cell and package it into a practical, self-contained, portable source of electrical energy — pre-loaded with its own reactants, unlike a fuel cell, which i…
Summary
- Electrochemical cells: a galvanic cell converts a spontaneous redox reaction into electrical energy; an electrolytic cell uses electrical energy to force a non-spontaneous redox reaction.
Sample & Board Papers
Sample papers and previous-year board questions for this subject.
+−Show 19 questionsHide questions19 questions
- Q1Arrange the following solutions in order of decreasing specific conductance: (i) 0.01 M NaCl (ii) 0.05 M NaCl (iii) 0.1 M NaCl (iv) 0.5 M Na…Preview
- Q2Which one is the SI unit of molar conductivity? (a) S m2 mol-1 (b) S m-1 (c) S cm2 mol-1 (d) S cm mol-1Preview
- Q3Write down the relation among the conductance and specific conductance of an electrolyte solution and the cell constant of the conductivity…Preview
- Q4Write the cell reaction and calculate the electrical work obtained from the following galvanic cell at standard condition: Mg | Mg2+(aq) ||…Preview
- Q5Charge carried by 1 mole of PO4^3- ions is: (a) 96500 C (b) 32167 C (c) 289500 C (d) 193000 CPreview
- Q6Arrange Li+, Na+ and Rb+ ions in the ascending order of their molar ionic conductance (λ°). **OR** What is the unit of electro-chemical equi…Preview
- Q7Calculate the equilibrium constant at 25 degC of the following equation of a Daniell cell: Zn(s) + Cu2+(aq) <=> Zn2+(aq) + Cu(s). [Given: E-…Preview
- Q8How many coulomb is the charge of 1 mol electron? **OR** How many coulomb of electricity is carried by Al3+ ion?Preview
- Q9Amount of electricity required to deposit one mole of Al from Al2O3 is (a) 1F (b) 6F (c) 3F (d) 2F (F = faraday)Preview
- Q10What is the unit of equivalent conductance? **OR** Which type of electric current DC or AC is used for measurement of conductivity of a solu…Preview
- Q11(i) State the Kohlrausch's law of independent migration of ions. (ii) The specific conductance or conductivity of a 0.01 M acetic acid at 29…Preview
- Q12Which is the SI unit of molar conductance? (a) S cm mol^-1 (b) Ohm cm mol^-1 (c) S m^2 mol^-1 (d) S m^-1Preview
- Q13What is specific conductance or conductivity? **OR** State whether lead-storage cell is primary battery or secondary battery.Preview
- Q14(i) Why does specific conductance or conductivity of a solution decrease on dilution? (ii) Represent the galvanic cell in which the followin…Preview
- Q15A galvanic cell reaction is spontaneous when (a) E°red < 0 (b) E°red > 0 (c) ΔG° < 0 (d) ΔG° > 0Preview
- Q16What is the SI unit of molar conductivity? **OR** Write the relation between specific conductivity and molar conductivity.Preview
- Q17(i) In button cell, widely used in watches, the following reaction takes place: Zn(s) + Ag2O(s) + H2O(l) → Zn2+(aq) + 2Ag(s) + 2OH⁻(aq). Det…Preview
- Q18Give the definition of specific conductance. Write the relation between molar conductance and specific conductance.Preview
- Q19i) What is fuel cell? ii) At 298 K the molar conductances of KCl and LiCl at infinite dilution are Λ°M(KCl) = 149.9 and Λ°M(LiCl) = 115.0 oh…Preview
More questions
33 Q+−Show 17 questionsHide questions17 questions
- Example 1A galvanic (voltaic) cell is set up by dipping a zinc rod into a $\text{ZnSO}_4$ solution and a copper rod into a $\text{CuSO}_4$ solution,…Free
- Example 4Write the cell notation (cell representation) for the Daniell cell consisting of a zinc electrode in $1\ \text{M}\ \text{ZnSO}_4$ and a copp…Free
- Example 6Using the standard reduction potentials $E^{\circ}(\text{Cu}^{2+}/\text{Cu}) = +0.34\ \text{V}$ and $E^{\circ}(\text{Zn}^{2+}/\text{Zn}) = -…Free
- Example 7Given the standard reduction potentials $E^{\circ}(\text{Fe}^{2+}/\text{Fe}) = -0.44\ \text{V}$, $E^{\circ}(\text{Zn}^{2+}/\text{Zn}) = -0.7…Preview
- Example 9For a Daniell cell $\text{Zn}(s)\,|\,\text{Zn}^{2+}(0.001\ \text{M})\,||\,\text{Cu}^{2+}(0.100\ \text{M})\,|\,\text{Cu}(s)$ at $298\ \text{K…Preview
- Example 11A Daniell cell $\text{Zn}(s)\,|\,\text{Zn}^{2+}(x\ \text{M})\,||\,\text{Cu}^{2+}(1\ \text{M})\,|\,\text{Cu}(s)$ has a measured EMF of $1.140…Preview
- Example 13Calculate the standard Gibbs energy change, $\Delta G^{\circ}$, for the Daniell cell reaction $\text{Zn}(s) + \text{Cu}^{2+}(aq) \to \text{Z…Preview
- Example 14Using $E^{\circ}_{cell} = 1.10\ \text{V}$ for the Daniell cell ($n=2$) at $298\ \text{K}$, calculate the equilibrium constant $K_c$ for the…Preview
- Example 15A conductivity cell filled with an electrolyte solution shows a resistance of $500\ \Omega$. If the cell constant is $1.15\ \text{cm}^{-1}$,…Preview
- Example 17A $0.20\ \text{M}$ solution of an electrolyte has a specific conductivity of $0.0248\ \text{S cm}^{-1}$ at $298\ \text{K}$. Calculate its mo…Preview
- Example 18Explain, with reference to the ionic-interaction picture, why the molar conductivity of a strong electrolyte such as $\text{KCl}$ increases…Preview
- Example 21Given the limiting molar conductivities $\Lambda_m^{0}(\text{HCl}) = 425.9\ \text{S cm}^2\ \text{mol}^{-1}$, $\Lambda_m^{0}(\text{CH}_3\text…Preview
- Example 23For $0.01\ \text{M}$ acetic acid, the degree of dissociation $\alpha = 0.0414$ (obtained from $\Lambda_m/\Lambda_m^{0}$). Calculate the diss…Preview
- Example 25A current of $2\ \text{A}$ is passed through molten copper(II) sulfate for $1930\ \text{s}$. Calculate the mass of copper deposited at the c…Preview
- Example 27Aluminium is extracted by the electrolysis of molten $\text{Al}_2\text{O}_3$ (Hall-Heroult process), in which $\text{Al}^{3+}$ is reduced to…Preview
- Example 30Describe the working of the hydrogen-oxygen fuel cell, and write the balanced half-reactions at the anode and the cathode (alkaline electrol…Preview
- Example 33Describe, in outline, the basic working principle of a lithium-ion (Li-ion) battery during discharge, naming the typical electrode materials…Preview
+−Show 16 questionsHide questions16 questions
- Q2A galvanic cell is built by combining a silver electrode dipped in $1\ \text{M}\ \text{AgNO}_3$ with a copper electrode dipped in $1\ \text{…Free
- Q3For the spontaneous reaction $\text{Zn}(s) + \text{Cu}^{2+}(aq) \to \text{Zn}^{2+}(aq) + \text{Cu}(s)$ that drives a Daniell cell, identify…Free
- Q5A cell is built from a nickel electrode dipped in $1\ \text{M}\ \text{NiSO}_4$ (anode) and a silver electrode dipped in $1\ \text{M}\ \text{…Free
- Q8Using $E^{\circ}(\text{Ag}^{+}/\text{Ag}) = +0.80\ \text{V}$ and $E^{\circ}(\text{Cu}^{2+}/\text{Cu}) = +0.34\ \text{V}$, predict whether me…Preview
- Q10For the cell $\text{Ni}(s)\,|\,\text{Ni}^{2+}(0.01\ \text{M})\,||\,\text{Ag}^{+}(1\ \text{M})\,|\,\text{Ag}(s)$ at $298\ \text{K}$, with $E^…Preview
- Q12A cell is constructed for the reaction $\text{Cu}(s) + \text{Zn}^{2+}(aq) \to \text{Cu}^{2+}(aq) + \text{Zn}(s)$ (the reverse of the Daniell…Preview
- Q16A $0.1\ \text{M}\ \text{KCl}$ solution, whose specific conductivity is $1.29\times10^{-2}\ \text{S cm}^{-1}$, is used to calibrate a conduct…Preview
- Q19State and explain why the molar conductivity of every electrolyte, strong or weak, increases as its solution is diluted.Preview
- Q20For a strong electrolyte, $\Lambda_m$ is found to vary linearly with $\sqrt{C}$ (Debye-Huckel-Onsager behaviour: $\Lambda_m = \Lambda_m^{0}…Preview
- Q22For a $0.01\ \text{M}$ solution of acetic acid, the molar conductivity $\Lambda_m$ is $16.18\ \text{S cm}^2\ \text{mol}^{-1}$. Taking $\Lamb…Preview
- Q24Given $\Lambda_m^{0}(\text{NH}_4\text{Cl}) = 150.0\ \text{S cm}^2\ \text{mol}^{-1}$, $\Lambda_m^{0}(\text{NaOH}) = 250.0\ \text{S cm}^2\ \te…Preview
- Q26A charge of $9650\ \text{C}$ is passed, in separate experiments, through molten $\text{AgNO}_3$ and molten $\text{CuSO}_4$. Calculate the ma…Preview
- Q28State Faraday's first law of electrolysis, and explain in your own words why it implies that the mass of a substance liberated at an electro…Preview
- Q29Write the products formed at the cathode and the anode when (a) molten sodium chloride and (b) aqueous sodium chloride (brine) are electroly…Preview
- Q31State two advantages of the hydrogen-oxygen fuel cell over a conventional fossil-fuel-burning power source, in terms of energy conversion ef…Preview
- Q32The common dry cell (Leclanche cell) used in torches has a zinc container as one electrode and a carbon rod surrounded by a paste of $\text{…Preview