Chemistry · Physics

Electrochemistry and Current Electricity

272 Questions

Review fundamental concepts of electrochemistry and current electricity through these practice questions. The set includes numerical problems on electrolysis, drift velocity, and electrode potentials. These topics frequently appear in engineering, CSIR NET, and state PSC prelims examinations for thorough preparation.

Electrolysis calculationsElectrode potentialNernst equationDrift velocityFuel cellsMolar conductivity

Electrochemistry and Current Electricity Questions

Multiple choice power transmission household electricity household circuits electricity and magnetism physics

A battery is charged at a potential of 15V for 8 hours when the current flowing is 10A. The battery on discharge supplies a current of 5A for 15 hours. The mean terminal voltage during discharges is 14 V. The "Watt hour" efficiency of the battery is :-

  1. 80%

  2. 90%

  3. 87.5%

  4. 82.5%
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

% Watt hour efficiency = $\frac{E _{out}} {E _{in}} \times 100$
= $\frac{\left ( 14 \right )\left ( 5 \right )\left ( 15 \right )} {\left ( 15 \right )\left ( 10 \right )\left ( 8 \right )} \times 100 = 87.5$%

Multiple choice physics magnetic effects of electric current direct current types of current movement of charge

Which of the following is wrong?

  1. It is not possible to have electrolysis by a.c.

  2. Ordinary batteries cannot be changed by a.c.

  3. In a circuit containing L, C and R in series across a steady source, poer is dissipated in R, at steady state

  4. For current dirven from a steady source by an ohmic conductor, mean value and r.m.s. value of current will be same
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

The negative Zn pole of Daniel cell, sending a constant current through a circuit, decreases in mass by 0.13 g in 30 minutes. If the chemical equivalent of Zn and Cu and 32.5 and 31.5 respectively, the increase in the mass of the positive Cu pole in this time is : 

  1. 0.180 g

  2. 0.141 g

  3. 0.126 g

  4. 0.242 g
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Faraday's laws of electrolysis, the mass deposited is proportional to the chemical equivalent. The mass of Cu deposited = (Mass of Zn lost * Equivalent weight of Cu) / Equivalent weight of Zn = (0.13 * 31.5) / 32.5 = 0.126 g.

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

The passage of electricity in the Daniell cell when $Zn$ and $Cu$ electrodes are connected is from:

  1. $Cu$ to $Zn$ in the cell
  2. $Cu$ to $Zn$ outside the cell
  3. $Zn$ to $Cu$ outside the cell
  4. $Zn$ to $Cu$ in the cell
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In Daniell cell, Zn acts an anode and Cu acts as cathode, electron flow takes place from anode to cathode and hence, electricity flows from Cu to Zn outside the cell.

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

Daniel cell operates under nonstandard state conditions. If the equation of the cell reaction is multiplied by 2 then:

  1. $E$ and $E^o$ remain unchanged
  2. $E$ is doubled
  3. $n$ remains unchanged in Nernst equation
  4. $Q$ is halved in Nernst equation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Nernst's equation states ${ E } _{ cell }={ E } _{ cell }^{ 0 }+\dfrac { RT }{ nF } ln\left[ { M }^{ + } \right] $

Where $E$ and ${ E }^{ 0 }$ of cell are independent of volume/quantity of reacting species in electrolyte, they are intunsic properties of cell. Hence, on doubling cell equation of Daniel cell.
$Zn\left| { Zn }^{ 2+ } \right| \left| { Cu }^{ 2+ } \right| Cu$,
its e.m.f $(E)$ and standard e.m.f $\left( { E }^{ 0 } \right) $ remain unchanged where ${ E }^{ 0 }$ stays at $1.09V$.

Multiple choice chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

For the Daniel cell involving the cell reaction${ Zn } _{ (s) }+{ { Cu }^{ +2 } } _{ (aq) }\rightleftharpoons { { { Zn }^{ +2 } } } _{ (aq) }+{ Cu } _{ (s) }$ the standard free energies of formation of  ${ Zn } _{ (s) }$, ${ Cu } _{ (s) }$, ${ { Cu }^{ +2 } } _{ (aq) }$ and ${ { { Zn }^{ +2 } } } _{ (aq) }$ are 0, 0, 64.4 KJ/Mole and -154.0 KJ/Mole, respectively. Calculate the standard EMF of the cell?

  1. $2.13 Volts$
  2. $1.13 Volts$
  3. $2.26 Volts$
  4. $3.42 Volts$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\because \quad \Delta { G }^{ 0 }=\left( { G } _{ { Zn }^{ 2+ } }^{ 0 }-{ G } _{ { Cu }^{ 2+ } }^{ 0 } \right) $ $= (-154-64.4) KJ/Mole$

$\therefore(-2\times{E}^{0}\times F)$ $=(-218.4\times {10}^3)$
$\therefore E^0=1.1316\quad volt$

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

The overall reaction of a hydrogen-oxygen fuel cell is:

  1. $2H _{2(g)}+O _{2(g)}\rightarrow 2H _2O _{(l)}$
  2. $2H _{2(g)}+4OH^- _{(aq)}\rightarrow 4H _2O _{(l)}+4e^-$
  3. $O _{2(g)}+2H _2O _{(l)}+4e^-\rightarrow 4OH^- _{(aq)}$
  4. $4OH^- _{(aq)}+4e^-\rightarrow 2H _2O _{(l)}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
A fuel cell is an electrochemical cell that converts the chemical energy from a fuel into electricity through an electrochemical reaction of hydrogen fuelwith oxygen or anotheroxidizing agent.
The reactions which takes place in hydrogen-oxygen fuel cell are,
At cathode:$2H _{2(g)}+4OH^{-} _{(aq)}\rightarrow 4H _2O _{(l)}+4e^{-}$
At cathode:$O _{2(g)}+2H _2O _{(l)}+4e^{-}\rightarrow 4OH^{-} _{(aq)}$
Overall reaction: $2H _{2(g)}+O _{2(g)}\rightarrow 2H _2O _{(l)}$

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

Which of the following statements is true for fuel cells ?

  1. They are more efficient

  2. They are free from pollution

  3. They run till reactants are active

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The fuel cells are more efficient. The energy efficiency of fuel cells is around 70 %. The only reaction product is water. Hence the fuel cells are free from pollution. The reactants are continuously supplied from external source. Hence fuel cells run till reactants are active.

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

The efficiency of a fuel cell is given by:

  1. $\frac{\Delta S}{\Delta G}$
  2. $\frac{\Delta H}{\Delta G}$
  3. $\frac{\Delta G}{\Delta S}$
  4. $\frac{\Delta G}{\Delta H}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The fuel cell thermodynamic efficiency is given by the ratio of the Gibbs function change to the Enthalpy change in the overall cell reaction. The Gibbs function change measures the electrical work and the enthalpy change is a measure of the heating value of the fuel. 
Efficiency = $ \frac{dG}{dH} $$=\frac{\Delta G}{\Delta H}$
Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

What is the approximate value of $ \Delta S^{\circ} $ for the fuel cell reaction at $ 25^{\circ}$? 

  1. $ -0.1624\,JK^{-1}$
  2. $ -162.4\,JK^{-1} $
  3. $ +162.4\,JK^{-1} $
  4. $ +0.1624\,JK^{-1} $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The question asks for the standard entropy change of a fuel cell reaction at 25°C but does not specify the reaction. Without knowing the specific fuel cell reaction (e.g., H2/O2, methanol, etc.), the value cannot be verified. The magnitude -162.4 JK^-1 is plausible for a multi-electron process like hydrogen oxidation but requires reaction context.

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

Identify the reaction taking place at cathode in fuel cell.

  1. ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}$
  2. $2{H} _{2}+4{OH}^{-}\rightarrow 4{H} _{2}O+4{e}^{-}$
  3. ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}+{H}^{+}$
  4. $4{H} _{2}O+4{e}^{-}\rightarrow 2{H}^{2}+4{OH}^{-}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a fuel cell the hydrogen enters the fuel cell at the anode. A chemical reaction strips the hydrogen molecules of their electrons and the atoms become ionized to form $H^+$. The electrons travel through wires to provide a current to do work. The oxygen enters at the cathode, usually from the air. The oxygen picks up the electrons that have completed their circuit. The oxygen then combines with the ionized hydrogen atoms $(H^+)$, and water $(H _2O)$ is formed as the waste product which exits the fuel cell. 
Cathode side (a reduction reaction): $O _2 + 4H^+ + 4e^- \rightarrow 2H _2O$
or ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}$