Tag: redox reactions and electrode processes

Questions Related to redox reactions and electrode processes

For the cell $Zn(s)|Zn^{2+}(aq)||Cu^{+2}(aq)|Cu(s)$. The cell potential $E _{cell}$ can be increased.

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

  1. By increasing $[Cu^{+2}]$

  2. By increasing $[Zn^{+2}]$

  3. By decreasing $[Cu^{+2}]$

  4. By decreasing $[Zn^{+2}]$

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Correct Option: A

In a Daniell cell:

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

  1. The chemical energy liberated during the redox reaction is converted to electrical energy

  2. The electrical energy of the cell is converted to chemical energy

  3. The energy of the cell is utilised in conduction of the redox reaction

  4. The potential energy of the cell is converted into electrical energy

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Correct Option: A
Explanation:

A galvanic cell is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell. It generally consists of two different metals connected by a salt bridge, or individual half-cells separated by a porous membrane. Daniel cell is a galvanic cell.

Daniel cell has Zn as anode and Cu as cathode. The reactions of Daniel cell are,

At anode(Oxidation),

$Zn(s)\rightarrow Zn^{2+}(aq)+2e^{-}$

At cathode(Reduction),

$Cu^{2+}(aq)+2e^{-}\rightarrow Cu(s)$

Hence overall reaction is,

$Zn(s)+Cu^{2+}(aq)\rightarrow Zn^{2+}(aq)+Cu(s)$

Here the chemical energy is liberated when the redox reaction takes place in the cell and it is converted into electrical energy.

Which one is not correct for e.m.f. of a galvanic cell?

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

  1. $E _{cell} = E _{OP _{anode}} + E _{RP _{cathode}}$

  2. $E _{cell} = E _{OP _{LHS}} + E _{RP _{RHS}}$

  3. $E _{cell} =$ higher oxidation potential - lower oxidation potential

  4. $E _{cell} =$ lower oxidation potential - higher oxidation potential

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Correct Option: A,B,C
Explanation:

The correct expressions for the standard cell potentials of a galvanic cell are as given below.
$E _{cell} = E _{OP _{anode}} + E _{OP _{cathode}}$
$E _{cell} = E _{OP _{LHS}} + E _{OP _{RHS}}$
$E _{cell} =$lower oxidation potential $-$ higher oxidation potential.
Thus, only option D is correct and options A to C are incorrect.

Identify the true statement regarding Daniel cell:

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

  1. Zinc ions flows across salt bridge 

  2. ${K}^{+}$ ions move from salt bridge to $Cu/{Cu}^{+2}$ half cell

  3. Oxidation takes place at copper electrode

  4. Flow of current takes place from copper electrode to zinc electrode

Show answer
Correct Option: D
Explanation:

Daniell cell is  perform the spontaneous redox reaction between zinc and cupric ions to produce an electric current. It consists of two half-cells. The  left half cell contains a zinc metal electrode dipped in $ZnSO _4$ solution.The half right half cell consists of copper metal electrode in a solution $CuSO _4$. The half-cells are joined by a salt bridge that prevents the mixing of the solution.
In Daniel cell flow of current takes place from copper electrode to zinc electrode.
Hence option D is correct.

For the galvanic cell, $Cu|Cu^{2+}||Ag^+|Ag$. Which of the following observations is not correct?

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

  1. Cu acts as anode and Ag acts as cathode

  2. Ag electrode loses mass and Cu electrode gains mass

  3. Reaction at anode, $Cu\rightarrow Cu^{2+}+2e^-$

  4. Copper is more reactive than silver

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Correct Option: B
Explanation:

Redox reactions are reactions in which both oxidation and reduction takes place together. In a Galvanic cell oxidation occurs at anode and reduction occurs at cathode. Here $Cu$ is an anode and $Ag$ is a cathode. As in Oxidation, the electrons get released to form aqueous ions in the solution and hence reduces the mass of the electrode as the electrons are released from the electrode. Here,$Cu$ electrode loses mass. Similarly,the released electrons are gained by silver ions i.e $Ag^ { +} $ and the electrode mass of $Ag$ gets increased. Hence, B is the wrong option.

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 : 

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

  1. 0.180 g

  2. 0.141 g

  3. 0.126 g

  4. 0.242 g

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Correct Option: C

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

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

  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

Show answer
Correct Option: B
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.

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

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

  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

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Correct Option: A
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 $1.09V$.

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?

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

  1. $2.13 Volts$

  2. $1.13 Volts$

  3. $2.26 Volts$

  4. $3.42 Volts$

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Correct Option: B
Explanation:

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

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

Which of the following statement is TRUE for the electrochemical Daniel cell :

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

  1. Electron flow from Zinc electrode to Copper electrode.

  2. Current flows from zinc electrode to copper electrode.

  3. Cation moves towards copper electrode.

  4. Cation moves towards zinc electrode.

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Correct Option: A
Explanation:

During reaction of $Zn\rightarrow{Zn}^{2+}+{2e}^{-}$ extra electron goes from anode to cathode or flow of $e^-$ from Zinc to Copper takes place and current flows from Copper to Zinc.