Question:medium

In an electrochemical cell, the standard electrode potential of \( \text{Zn}^{2+}/\text{Zn} \) is \( -0.76 \, \text{V} \) and that of \( \text{Cu}^{2+}/\text{Cu} \) is \( +0.34 \, \text{V} \). What is the standard EMF of the cell formed by these electrodes?

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To calculate the EMF of a galvanic cell, subtract the standard reduction potential of the anode from that of the cathode. A positive EMF indicates a spontaneous cell reaction.
Updated On: Nov 26, 2025
  • \( 0.42 \, \text{V} \)
  • \( 1.10 \, \text{V} \)
  • \( -1.10 \, \text{V} \)
  • \( -0.42 \, \text{V} \)
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The Correct Option is B

Solution and Explanation

The standard electromotive force (EMF) of an electrochemical cell is determined by the difference between the standard electrode potentials of the cathode and anode, as expressed by the equation:\[\text{EMF} = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}}\]In this formula:- \( E^\circ_{\text{cathode}} \) denotes the standard reduction potential at the cathode, where reduction occurs.- \( E^\circ_{\text{anode}} \) denotes the standard reduction potential at the anode, where oxidation occurs.The provided standard electrode potentials are:- For \( \text{Zn}^{2+}/\text{Zn} \): \( -0.76 \, \text{V} \)- For \( \text{Cu}^{2+}/\text{Cu} \): \( +0.34 \, \text{V} \).In a galvanic cell, the half-cell with the higher standard reduction potential functions as the cathode (site of reduction), while the half-cell with the lower standard reduction potential acts as the anode (site of oxidation). Comparing the given potentials:- \( E^\circ (\text{Cu}^{2+}/\text{Cu}) = +0.34 \, \text{V} \) is the higher potential, thus designated as the cathode.- \( E^\circ (\text{Zn}^{2+}/\text{Zn}) = -0.76 \, \text{V} \) is the lower potential, thus designated as the anode.The cell representation is:\[\text{Zn} | \text{Zn}^{2+} || \text{Cu}^{2+} | \text{Cu}\]The standard EMF is calculated as:\[\text{EMF} = E^\circ_{\text{Cu}^{2+}/\text{Cu}} - E^\circ_{\text{Zn}^{2+}/\text{Zn}}\]Substituting the values:\[\text{EMF} = 0.34 \, \text{V} - (-0.76 \, \text{V}) = 0.34 \, \text{V} + 0.76 \, \text{V} = 1.10 \, \text{V}\]A positive EMF value signifies that the cell reaction proceeds spontaneously as depicted.Therefore, the standard EMF of the described cell is \( 1.10 \, \text{V} \).
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