Redox Reactions and Electrochemistry — CBSE Class 12 board PYQs

Which of the following cells is used in the Apollo space programme?

Dilution affects both conductivity as well as molar conductivity. The effect of dilution on both is as follows:

Which one of the following cells was used in the Apollo space programme?

Consider the following standard electrode potential values:


What is th …

A voltaic cell is made by connecting two half cells represented by the half equations below:


Which statem …

Four half reactions I to IV are shown below:
I. $2\mathrm{C}{\mathrm{l}}^{-}\to \mathrm{C}{\mathrm{l}}_2+2e^{-}$
II. $4\mathrm{O}{\mathrm{H}}^{-}\to {\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}+4e^{-}$
III. $\mathrm{N}{\mathrm{a}}^{+}+e^{-}\to \mathrm{Na}$
IV. $2{\mathrm{H}}^{+}+2e^{-}\to {\mathrm{H}}_2$
Which two of these reaction …

Out of zinc and tin, whose coating is better to protect iron objects?

Express the relation between conductivity and molar conductivity of a solution held in a cell.

What is meant by limiting molar conductivity?

What is meant by a primary battery? Give an example.

How does the molar conductivity of KCl solution vary with increasing concentration?

Write the relation between cell potential and equilibrium constant.

Why is the equilibrium constant K related only to $E_{cell}^{\circ }$ and not to $E_{cell}$?

Write the Nernst equation for a single electrode potential.

In an aqueous solution, how does the specific conductivity of an electrolyte change with dilution?

Write the symbolic notation for the standard hydrogen electrode and its potential.

Which type of metal can be used in cathodic protection of iron against rusting?

How does a fuel cell operate?

Give an example of a fuel cell.

Write the Nernst equation for the electrode reaction:

Under what conditions will a galvanic cell send no current into the outer circuit?

Electrolysis of KBr(aq) gives Br${}_2$ at the anode, but that of KF(aq) does not give F${}_2$. Give reason for this disparity.

How does cathodic protection of iron operate?

What is the effect of increase in concentration of zinc ions on the electrode potential of zinc electrode, for which $E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.76$ V?

Why is it that aluminium metal cannot be obtained by electrolysis of an aqueous solution of a salt of aluminium?

At infinite dilution, the molar conductances of Na${}^{+}$ and SO${}_4^{2-}$ ions are 50 S cm${}^2$ mol${}^{-1}$ and 160 S cm${}^2$ mol${}^{-1}$ respectively. What will be the molar conductance of sodium sulphate at infinite dilution?

Why does an alkaline medium inhibit the rusting of iron?

How many faradays of electricity are required to liberate two moles of hydrogen gas in the electrolysis of a solution?

In the operation of a galvanic cell, at one of the electrodes oxidation takes place. What is the name of this electrode and what is its polarity?

What does the standard potential of a metal being negative ($E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.76$ V) indicate?

State Kohlrausch law for electrical conductance of an electrolyte at infinite dilution.

State the following:
(a) Kohlrausch law of independent migration of ions
(b) Faraday's first law of electrolysis

The resistance of a conductivity cell filled with 0.2 mol L${}^{-1}$ KCl solution is 200 Ω. If the resistance of the same cell when filled with 0.05 mol L${}^{-1}$ KCl solution is 620 Ω, calculate the conductivity and molar conductivity of the 0.05 mol L${}^{-1}$ KCl solution. The cond …

Calculate the emf of the following cell:

Given: $E_{cell}^{\circ }=1.05$ V, log 10 = 1.

Read the passage carefully and answer the questions that follow:
Rahul set up an experiment to find the resistance of aqueous KCl solution for different concentrations at 298 K using a conductivity cell connected to a Wheatstone bridge, fed with A.C. power in the audio frequency …

(a) The cell in which the following reaction occurs:

has $E_{cell}^{\circ }=0.236$ V at 298 K. Calculate the standard Gibbs energy of the cell reaction. (Given: 1 F = 96500 C mol${}^{-1}$)
(b) How many electrons …

Write the name of the cell which is generally used in hearing aids. Write the reactions taking place at the anode and the cathode of this cell.

From the given cells — lead storage cell, mercury cell, fuel cell and dry cell — answer the following:
i) Which cell is used in hearing aids?
ii) Which cell was used in the Apollo Space Programme?
iii) Which cell is used in automobiles and inverters?
iv) Which cell does not have …

a) The following reactions can occur at the cathode during the electrolysis of aqueous silver chloride solution:
…

Calculate the emf of the following cell at 25°C:

$E^{\circ }(\mathrm{F}{\mathrm{e}}^{2+}|Fe)=-0.44$ V, $E^{\circ }({\mathrm{H}}^{+}|{\mathrm{H}}_2)=0.00$ V.

Calculate the e.m.f. of the following cell at 298 K:

Given: $E^{\circ }(\mathrm{C}{\mathrm{r}}^{3+}|Cr)=-0.74$ V, $E^{\circ }(\mathrm{F}{\mathrm{e}}^{2+}|Fe)=-0.44$ V.

Give an example of a fuel cell and write the cathode and anode reactions for it.

Mention the reactions occurring at (i) anode, (ii) cathode, during the working of a mercury cell. Why does the voltage of a mercury cell remain constant during its operation?

The chemistry of corrosion of iron is essentially an electrochemical phenomenon. Explain the reactions occurring during the corrosion of iron in the atmosphere.

Calculate the equilibrium constant K for the reaction at 298 K:

(Given: $E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.76$ V, $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=+0.34$ V)

For the cell

a) write the equation for each half-reaction,
b) calculate the cell potential at 25°C.
(Given: $E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.76$ V, $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=+0.34$ V)

Two half-reactions of an electrochemical cell are given below:


Construct the red …

Given that the standard electrode potentials (E°) of metals are:
K${}^{+}$/K = −2.93 V, Ag${}^{+}$/Ag = 0.80 V, Cu${}^{2+}$/Cu = 0.34 V, Mg${}^{2+}$/Mg = −2.37 V, Cr${}^{3+}$/Cr = −0.74 V, Fe${}^{2+}$/Fe = −0.44 V.
Arrange these metals in an increasing order of their reducing power.

Express the relation among the cell constant, the resistance of the solution in the cell and the conductivity of the solution. How is the conductivity of a solution related to its molar conductivity?

What is a nickel–cadmium cell? State its one merit and one demerit over the lead storage cell. Write the overall reaction that occurs during the discharging of this cell.

Calculate the emf of the cell in which the following reaction takes place:

Given: $E_{cell}^{\circ }=1.05$ V.

What type of cell is the lead storage battery? Write the anode and the cathode reactions and the overall cell reaction occurring in the use of a lead storage battery.

A copper–silver cell is set up. The copper ion concentration in it is 0.10 M. The concentration of silver ion is not known. The cell potential measured is 0.422 V. Determine the concentration of silver ion in the cell.
(Given: $E_{\mathrm{A}{\mathrm{g}}^{+}/Ag}^{\circ }=+0.80$ V, …

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

Depict the galvanic cell in which the reaction

takes place. Further indicate what are the carriers of current inside and outside the cell. State the reaction at each electrode.

The conductivity of a 0.20 M solution of KCl at 298 K is 0.0248 S cm${}^{-1}$. Calculate its molar conductivity.

Depict the galvanic cell in which the reaction

takes place. Which of its electrodes is negatively charged?

On the basis of the standard electrode potential values stated for acid solution, predict whether Ti${}^{4+}$ species may be used to oxidise Fe(II) to Fe(III):
…

Define electrical conductivity and molar conductivity of a solution and write the units of molar conductivity.

Calculate the standard cell potential of the galvanic cell in which the following reaction takes place:

Also calculate the ΔG° value of the reaction.
(Given: $E_{\mathrm{C}{\mathrm{r}}^{3+}/Cr}^{\circ }=-0.74$ V; …

What are fuel cells? Write the electrode reactions of a fuel cell which uses the reaction of hydrogen with oxygen.

a) At 291 K, the molar conductivities at infinite dilution of NH${}_4$Cl, NaOH and NaCl are 129.8, 217.4 and 108.9 ohm${}^{-1}$ cm${}^2$ mol${}^{-1}$ respectively. If the molar conductivity of a centinormal solution of NH${}_4$OH is 9.33 ohm${}^{-1}$ cm${}^2$ mol${}^{-1}$, what is the degree of …

Calculate the emf of the following cell at 298 K:

Given: $E_{\mathrm{F}{\mathrm{e}}^{2+}/Fe}^{\circ }=-0.44$ V, $E_{\mathrm{A}{\mathrm{g}}^{+}/Ag}^{\circ }=0.80$ V, R = 8.31 J K${}^{-1}$ mol${}^{-1}$, 1 F = 96500 C mol${}^{-1}$

Calculate the equilibrium constant for the following reaction at 298 K:

Given: R = 8.314 J K${}^{-1}$ mol${}^{-1}$, $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=0.34$ V, $E_{\frac{1}{2}\mathrm{C}{\mathrm{l}}_2/C{\mathrm{l}}^{-}}^{\circ }=1.36$ V, 1 F = 96500 C mol …

Calculate the emf of the following cell:

$E_{\mathrm{A}{\mathrm{g}}^{+}/Ag}^{\circ }=0.80$ V, $E_{\mathrm{M}{\mathrm{g}}^{2+}/Mg}^{\circ }=-2.37$ V

A zinc rod is dipped in a 0.1 M solution of ZnSO${}_4$. The salt is 95% dissociated at this dilution at 298 K. Calculate the electrode potential. (Given: $E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.76$ V)

What are fuel cells? How do they resemble and differ from galvanic cells?

Predict the products of electrolysis obtained at the electrodes in each case when the electrodes used are of platinum:
i) an aqueous solution of AgNO${}_3$
ii) an aqueous solution of H${}_2$SO${}_4$

What is corrosion? Describe the electrochemical phenomenon of rusting of iron.

In the button cell widely used in watches and other devices, the following reaction takes place:

Determine E° and ${\Delta }_r{G}^{\circ }$ for the reaction.
(Given $E_{\mathrm{A}{\mathrm{g}}_{2}O/Ag}^{\circ }=0.80$ V, …

The emf of the cell

has been found to be 0.3305 V at 298 K. Calculate the value of M${}_1$. Given: $E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.76$ V, $E_{\mathrm{C}{\mathrm{d}}^{2+}/Cd}^{\circ }=-0.40$ V.

Silver is electrodeposited on a metallic vessel of surface area 800 cm${}^2$ by passing a current of 0.2 A for 3 hours. Calculate the thickness of silver deposited. (Density of silver = 10.47 g cm${}^{-3}$, atomic mass of silver = 107.92 u)

When a certain conductivity cell was filled with 0.1 M KCl, it had a resistance of 85 Ω at 25°C. When the same cell was filled with an aqueous solution of 0.052 M of an unknown electrolyte, the resistance was 96 Ω. Calculate the molar conductivity of the unknown electrolyte at th …

Calculate the equilibrium constant for the reaction:

(Given: $E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.763$ V and $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=+0.34$ V)

Write the Nernst equation and calculate the emf of the following cell at 298 K:

(Given: $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=+0.34$ V and $E_{\mathrm{A}{\mathrm{g}}^{+}/Ag}^{\circ }=+0.80$ V)

Write the Nernst equation and calculate the e.m.f. of the following cell at 298 K:

Given: $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=0.34$ V and $E_{\mathrm{A}{\mathrm{g}}^{+}/Ag}^{\circ }=+0.80$ V.

a) Calculate the electrode potential of a silver electrode dipped in a 0.1 M solution of silver nitrate at 298 K, assuming silver nitrate to be completely dissociated. The standard electrode potential of Ag${}^{+}$/Ag is 0.80 V at 298 K.
b) At what concentration of silver ions will t …

Calculate the cell emf at 25°C for the following cell:

(Given $E_{\mathrm{Z}{\mathrm{n}}^{2+}/Zn}^{\circ }=-0.76$ V, $E_{\mathrm{P}{\mathrm{b}}^{2+}/Pb}^{\circ }=-0.13$ V, 1 F = 96500 C mol${}^{-1}$)
Calculate the maximum work that …

Calculate the emf and ΔG of the cell reaction for the following cell at 25°C:

($E_{\mathrm{M}{\mathrm{g}}^{2+}/Mg}^{\circ }=-2.34$ V; $E_{\mathrm{S}{\mathrm{n}}^{2+}/Sn}^{\circ }=-0.136$ V; 1 F = 96500 C mol${}^{-1}$)

Calculate the emf at 25°C for the following cell:

(Given $E_{\mathrm{N}{\mathrm{i}}^{2+}/Ni}^{\circ }=-0.25$ V, $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=+0.34$ V, 1 F = 96500 C mol${}^{-1}$)
Calculate the maximum work that can …

The measured resistance of a conductance cell containing a $7.5\times 10^{-3}$ M solution of KCl at 25°C was 1005 ohms. Calculate (a) the specific conductance and (b) the molar conductance of the solution. (Cell constant = 1.25 cm${}^{-1}$)

Calculate the emf and ΔG of the cell reaction for the following cell at 25°C:

($E_{\mathrm{M}{\mathrm{g}}^{2+}/Mg}^{\circ }=-2.37$ V; $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=+0.34$ V; 1 F = 96500 C mol${}^{-1}$)

(a) Calculate ΔG° for the reaction

Given: E° for Zn${}^{2+}$/Zn = −0.76 V, E° for Cu${}^{2+}$/Cu = +0.34 V, R = 8.314 J K${}^{-1}$ mol${}^{-1}$, F = 96500 C mol${}^{-1}$.
(b) Give two advantages of fuel cells.

(a) Out of the following pairs, predict with reason which pair will allow greater conduction of electricity:
(i) silver wire at 30°C or silver wire at 60°C;
(ii) 0.1 M CH${}_3$COOH solution or 1 M CH${}_3$COOH solution;
(iii) KCl solution at 20°C or KCl solution at 50°C.
(b) Give two …

Read the passage given below and answer the questions that follow:
Redox reactions involve transfer of electrons from one species to another. In a spontaneous reaction, energy is released and can be used to do useful work. The reaction is split into two half-reactions in two cont …

$E_{cell}^{\circ }$ for the given redox reaction is 2.71 V:

Calculate $E_{cell}$ for the reaction. Write the direction of flow of current when an external opposite potential applied is
(i) less than 2.71 V …

(a) A steady current of 2 amperes was passed through two electrolytic cells X and Y connected in series, containing electrolytes FeSO${}_4$ and ZnSO${}_4$, until 2.8 g of Fe deposited at the cathode of cell X. How long did the current flow? Calculate the mass of Zn deposited at the c …

(a) Write the cell reaction and calculate the e.m.f. of the following cell at 298 K:

(Given: $E_{\mathrm{S}{\mathrm{n}}^{2+}/Sn}^{\circ }=-0.14$ V)
(b) Give reasons:
(i) On the basis of E° values, O …

(a) Calculate $E_{cell}^{\circ }$ for the following reaction at 298 K:

Given: $E_{cell}=0.261$ V.
(b) Using the E° values of A and B, predict which one is better for coating the surface of iron [E°(Fe …

(a) The conductivity of a 0.001 mol L${}^{-1}$ solution of CH${}_3$COOH is $3.905\times 10^{-5}$ S cm${}^{-1}$. Calculate its molar conductivity and degree of dissociation (α).
Given: λ°(H${}^{+}$) = 349.6 S cm${}^2$ mol${}^{-1}$ and λ°(CH${}_3$COO${}^{-}$) = 40.9 S cm${}^2$ mol${}^{-1}$.
(b) Define elec …

The standard electrode potential (E°) for the Daniell cell is +1.1 V. Calculate ΔG° for the reaction

(1 F = 96500 C mol${}^{-1}$)

Calculate the emf of the following cell at 25°C:

Given: $E_{cell}^{\circ }=+0.46$ V and log 10${}^n$ = n.

a) What type of battery is the lead storage battery? Write the anode and cathode reactions and the overall cell reaction occurring in the operation of a lead storage battery.
b) Calculate the potential for the half-cell containing 0.10 M K${}_2$Cr${}_2$O${}_7$(aq), 0.20 M Cr${}^{3+}$(aq) …

a) State Kohlrausch law of independent migration of ions. Write an expression for the molar conductivity of acetic acid at infinite dilution according to Kohlrausch law.
b) Calculate ${\Lambda }_m^{\circ }$(CH${}_3$COOH), given that ${\Lambda }_m^{\circ }$(HCl) = 426 S cm${}^2$ mol${}^{-1}$, …

a) How many moles of mercury will be produced by electrolysing a 1.0 M Hg(NO${}_3$)${}_2$ solution with a current of 2.00 A for 3 hours? [Hg(NO${}_3$)${}_2$ = 200.6 g mol${}^{-1}$]
b) A voltaic cell is set up at 25°C with the half-cells Al${}^{3+}$(0.001 M) | Al and Ni${}^{2+}$(0.50 M) | Ni. W …

a) State the relationship among the cell constant of a cell, the resistance of the solution in the cell and the conductivity of the solution.
b) A voltaic cell is set up at 25°C with the following half-cells: Al | Al${}^{3+}$(0.001 M) and Ni | Ni${}^{2+}$(0.50 M). Calculate the cell …

a) Define molar conductivity of a substance and describe how, for weak and strong electrolytes, molar conductivity changes with the concentration of the solute. How is this change explained?
b) A voltaic cell is set up at 25°C with the following half-cells: Ag${}^{+}$(0.001 M) | Ag a …

a) Write the anode and cathode reactions and the overall reaction occurring in a lead storage battery.
b) A copper–silver cell is set up. The copper ion concentration is 0.10 M. The concentration of silver ion is not known. The cell potential measured is 0.422 V. Determine the co …

Three electrolytic cells A, B and C containing solutions of zinc sulphate, silver nitrate and copper sulphate respectively are connected in series. A steady current of 1.5 ampere was passed through them until 1.45 g of silver were deposited at the cathode of cell B. How long did …

The conductivity of a 0.00241 M acetic acid solution is $7.896\times 10^{-5}$ S cm${}^{-1}$. Calculate its molar conductivity in this solution. If ${\Lambda }_m^{\circ }$ for acetic acid is 390.5 S cm${}^2$ mol${}^{-1}$, what would be its dissociation constant?

Calculate the emf of the cell:

(Given: $E_{\mathrm{C}{\mathrm{u}}^{2+}/Cu}^{\circ }=+0.34$ V, $E_{\mathrm{M}{\mathrm{g}}^{2+}/Mg}^{\circ }=-2.37$ V)

i) The resistance of a conductivity cell containing 0.001 M KCl solution at 298 K is 1500 Ω. What is the cell constant if the conductivity of 0.001 M KCl solution at 298 K is $0.146\times 10^{-3}$ S cm${}^{-1}$?
ii) Predict the products of electrolysis in the following: a solution o …

i) Explain with an example how weak and strong electrolytes can be distinguished.
ii) In the button cell used in watches the following reaction occurs:

Determine E° for the cell and …

i) Define the terms specific conductance and molar conductivity for solutions of electrolytes.
ii) Write the cell formulation and calculate the standard cell potential for the galvanic cell in which the following reaction takes place: …

a) Give reasons for the following:
i) Rusting of iron is quicker in saline water than in ordinary water.
ii) Aluminium metal cannot be produced by the electrolysis of an aqueous solution of an aluminium salt.
b) The resistance of a conductivity cell filled with 0.1 M KCl solution …

i) Account for the following:
(a) An alkaline medium inhibits the rusting of iron.
(b) Iron does not rust even if the zinc coating is broken in a galvanised iron pipe.
ii) Given: $\mathrm{C}{\mathrm{u}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Cu}$, E° = +0.34 V; $\mathrm{A}{\mathrm{g}}^{+}+{\mathrm{e}}^{-}\to \mathrm{Ag}$, E° = +0.80 V. …

i) State two advantages of the H${}_2$–O${}_2$ fuel cell over an ordinary cell.
ii) Silver is electrodeposited on a metallic vessel of total surface area 900 cm${}^2$ by passing a current of 0.5 A for two hours. Calculate the thickness of silver deposited.
(Given: density of silver = 1 …

i) Explain why electrolysis of an aqueous solution of NaCl gives H${}_2$ at the cathode and Cl${}_2$ at the anode. Write the overall reaction.
($E_{\mathrm{N}{\mathrm{a}}^{+}/Na}^{\circ }=-2.71$ V; $E_{{\mathrm{H}}_{2}O/{\mathrm{H}}_2}^{\circ }=-0.83$ V; $E_{\mathrm{C}{\mathrm{l}}_2/2C{\mathrm{l}}^{-}}^{\circ }=+1.36$ V; …