Problem: A voltaic cell using a standard hydrogen electrode (SHE). The anode half-cell is Zn metal in a Zn(NO3)2 (aq) solution, and the cathode half-cell is the SHE in an HNO3(aq) solution.Why do Na+ ions migrate into the cathode half-cell as the cell reaction proceeds?

FREE Expert Solution

We have to determine why the Naions migrate into the cathode half-cell as the cell reaction proceeds.


Step 1. Write the two half-cell reactions and determine the half-cell potentials (refer to the Standard Reduction Potential Table)
Step 2. Identify the reduction half-reaction (cathode) and the oxidation half-reaction (anode)

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Problem Details

Two beakers are filled with liquid, and are connected by a salt bridge.  The beaker on the left is the anode half-cell, and contains a Zn anode while the beaker on the right is the cathode half-cell, and contains the standard hydrogen electrode (SHE).  The SHE is a glass tube filled with H2 gas that contains a thin wire. The reaction in the left beaker is Zn (solid) goes to Zn2+ (aqueous) plus 2 e-.  The reaction in the right beaker is H+ (aqueous) plus 2 e- goes to H2 (gas).  A voltmeter is connected to both electrodes; electron flow through the voltmeter is from the Zn anode toward the SHE cathode, and registers 0.76 volts.  Through the salt bridge, NO3- migrates toward the anode and Na+ migrates toward the cathode.
A voltaic cell using a standard hydrogen electrode (SHE). The anode half-cell is Zn metal in a Zn(NO3)(aq) solution, and the cathode half-cell is the SHE in an HNO3(aq) solution.

Why do Na+ ions migrate into the cathode half-cell as the cell reaction proceeds?

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