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Redox reactions and electrode processes - class-XI

Description: Redox reactions and electrode processes
Number of Questions: 15
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Tags: oxidation- reduction reactions redox reactions chemistry
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The life span of a Daniel cell may increased by:

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

  1. large Cu electrode

  2. lowering of CuSO$ _{4}$ concentration

  3. lowering of ZnSO$ _{4}$ concentration

  4. large zinc electrode

Show answer
Correct Option: D
Explanation:

In a daniel cell at anode Zn gets converted to $Zn^{2+}$
$\therefore$ If the size of electrode is increases more zinc can be oxidized,
hence the life span of the cell may be increased

Hence, option d is correct.

Estimate the cell potential of a Daniel cell having $1.0 M - Zn^{2+}$ and originally having $ 1.0 M - Cu^{2+}$ after sufficient ammonia has been added to the cathode compartment to make the $ NH _{3}$ concentration 2.0 M. Given: $ _{zn^{2+}|Zn}^{0} = 0.76 V, E _{Cu^{2+}|Cu}^{0} = + 0.34 V, K _{f}$ for $ Cu (NH _{3}) _{4}^{2+} = 1 \times 10^{12}.$

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

  1. 1.10 V

  2. 0.704 V

  3. 0.396 V

  4. 1.496 V

Show answer
Correct Option: B

The passage of electricity in the Daniel cell when Zn and Cu electrodes are connected 

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

  1. from Cu to Zn inside the cell

  2. from Cu to Zn outside the cell

  3. from Zn to Cu inside the cell

  4. from Zn to Cu outside the cell

Show answer
Correct Option: B,C

In a Daniel cell when $Cu$ and $Zn$ electrodes are connected current flows from:

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

  1. $Cu$ to $Zn$ within the cell

  2. $Cu$ to $Zn$ outside the cell

  3. $Zn$ to $Cu$ outside the cell

  4. all of the above

Show answer
Correct Option: C
Explanation:
We know outside the cell, electron flow from anode to cathode in the external current. Chemical energy is converted into electrical energy. The net reaction is the sum of two half-cell reactions.

For daniel cell, $Zn$ is at the anode and $Cu$ at the cathode.
The electron current flows from Zn to Cu.

So, the correct option is ( C )

In the electrochemical cell $H _{2}(g),1atm|H^{+}(1M)||Cu^{2+}(1M)|Cu(s)$, which one of the following statements is true? 

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

  1. H$ _{2}$ is cathode, Cu is anode

  2. Oxidation occurs at Cu electrode

  3. Reduction occurs at H$ _{2}$ electrode

  4. H$ _{2}$ is anode, Cu is Cathode

Show answer
Correct Option: D
Explanation:

At anode oxidation takes place and at cathode reduction take place
$\therefore H _2$ is anode and Cu is cathode

The standard EMF of a Daniel cell at 298 K is $E _{1}$. When the concentration of $ZnSO _{4}$ is 1.0 M and that of $CuSO _{4}$ is 0.01 M, the EMF becomes $E _{2}$ at 298 K. The correct relationship between $E _{1}$ and $E _{2}$ is

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

  1. $E _{1} = E _{2}$

  2. $E _{2}=0$

  3. $E _{1} > E _{2}$

  4. $E _{1} < E _{2}$

Show answer
Correct Option: C

If a current of 1.0 A is drawn from the Daniel cell for 96.5 min, the cathode will gain in weight by (Cu = 63.5, Zn = 65.4)

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

  1. 1.905 g

  2. 1.962 g

  3. 3.81 g

  4. 3.924 g

Show answer
Correct Option: A

If a battery of $1.6V$ is connected to Daniel cell, current flows:

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

  1. into the cell

  2. out of the cell

  3. neither in nor out of the cell

  4. both ways

Show answer
Correct Option: B
Explanation:

Flow of current occurs when there is voltage drop.Voltage drop happens when there is imbalance in charge. Daniel cell has voltage $1.5V$. If a battery of $1.6V$is connected to the Daniel cell. There is a flow of current out of the cell. 

Electrochemical Battery

An electrochemical battery is a device powered by oxidation and reduction reactions that are physically separated. So that the electrons must travel through a wire from the reducing agent to the oxidizing agent. 

The reducing agent loses electrons and is oxidized in a reaction that takes place at an electrode is called the anode. The oxidizing agent gains electrons and is reduced in a reaction that takes at an electrode is called the cathode.  

To maintain a net zero charge in each compartment, there is a limited flow of ions through a salt bridge. 
For example, in a car battery the reducing agent is oxidized by the following reaction, which involves a lead ( $Pb$ ) anode and sulfuric acid ( $H _2SO _4$). Lead sulfate ( $PbSO _4$ ), protons ( $H$ ), and electrons ( $e^-$) are produced.

At the cathode, the below reaction occurs :

$PbO _2+H _2SO _4+2H^++2e^-\rightarrow$ PbSO_4+2H_2O$
 
At the anode, the below reaction occurs :

$Pb+H_2SO_4 \rightarrow PbSO_4+2H^++2e^-$

Electrons are produced by a chemical reaction that takes place at the:

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

  1. anode.

  2. cathode.

  3. lead oxide electrode.

  4. oxidizer.

  5. salt bridge.

Show answer
Correct Option: A
Explanation:

At the anode, oxidation of metal takes place;

oxidation is the process of removal of the electron;

So, the electrons that are produced in the chemical reaction take place at the anode.

Hence, option (A) is correct

Assertion: In a Daniell cell, electrons flow from zinc electrode to copper electrode outside the cell.
Reason: In Daniell cell, Zn electrode is anode and Cu is cathode.
chemistry oxidation- reduction reactions redox reactions and electrode processes redox and electrode processes applications of redox reaction

  1. Both Assertion and Reason are true and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

  3. Assertion is true but Reason is false

  4. Assertion is false but Reason is true

  5. Both Assertion and Reason are false

Show answer
Correct Option: D
Explanation:

In a Daniell cell, Zn is anode
So $e^{-}$ flow from Zn to Cu electrode.

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 $[Zn^{+2}]$

Show answer
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

Show answer
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

Show answer
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

Show answer
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.

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