Tag: chemistry

Questions Related to chemistry

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

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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

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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

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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

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

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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

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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

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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.

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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

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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 $[Zn^{+2}]$

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Correct Option: A