Question:

For the Daniel cell, $Zn\left| Zn^{2+}\right|\left| Cu^{2+}\right| Cu$ with $E_{\text{cell}} = 1 . 1\, V$, the application of opposite potential greater than $1 . 1\, V$ results into flow of electron from cathode to anode. $Zn$ is deposited at anode and $Cu$ is dissolved at cathode.

Updated On: Jul 2, 2022
  • If both assertion and reason are true and reason is the correct explanation of the assertion
  • If both assertion and reason are true but reason is not the correct explanation of the assertion
  • If assertion is true, but reason is false
  • Both assertion and reason are false statements
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The Correct Option is B

Solution and Explanation

Both (A) and (R) are correct but (R) is not the correct explanation of (A) . Correct explanation: On applying an external voltage greater than $1.1 V$ in a Daniell cell, the current flows in the reverse direction i.e., from $Zn$ to $Cu$ (cathode to anode) and electrons flow from $Cu$ and $Zn$. $Zn$ is deposited at $Zn$ electrode and $Cu$ dissolves at $Cu$ electrode. The reaction is: $Zn ^{2+}+ Cu \rightarrow Zn + Cu ^{2+}$
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Concepts Used:

Electrochemical Cells

An electrochemical cell is a device that is used to create electrical energy through the chemical reactions which are involved in it. The electrical energy supplied to electrochemical cells is used to smooth the chemical reactions. In the electrochemical cell, the involved devices have the ability to convert the chemical energy to electrical energy or vice-versa.

Classification of Electrochemical Cell:

Cathode

  • Denoted by a positive sign since electrons are consumed here
  • A reduction reaction occurs in the cathode of an electrochemical cell
  • Electrons move into the cathode

Anode

  • Denoted by a negative sign since electrons are liberated here
  • An oxidation reaction occurs here
  • Electrons move out of the anode

Types of Electrochemical Cells:

Galvanic cells (also known as Voltaic cells)

  • Chemical energy is transformed into electrical energy.
  • The redox reactions are spontaneous in nature.
  • The anode is negatively charged and the cathode is positively charged.
  • The electrons originate from the species that undergo oxidation.

Electrolytic cells

  • Electrical energy is transformed into chemical energy.
  • The redox reactions are non-spontaneous.
  • These cells are positively charged anode and negatively charged cathode.
  • Electrons originate from an external source.