A voltaic cell is created by using a copper cathode and a magnesium anode. The cathode is immersed in a solution of Cu2 ions, and the anode is immersed in a solution of Mg2 ions. A salt bridge of Na2SO4 is also used. What happens to the ions in the salt bridge as the reaction proceeds

As the reaction proceeds in the given voltaic cell, the Na₂SO₄ present in the salt bridge will dissociate into Na⁺ and SO₄²⁻ ions. As the copper ions in the solution are being deposited on the copper cathode as neutral copper atoms, the solution will become more negative, therefore the Na⁺ ions in the salt bridge will migrate into the the solution in order to maintain electrical neutrality. At the anode, as the Mg metal dissolve into the solution as Mg⁺² ions, the  solution will tend to become more positive. Therefore, the SO₄²⁻ ions present in the salt bridge will migrate into the solution in order to maintain electrical neutrality.

Explanation:

A voltaic or galvanic cell is an example of an electrochemical cell.

An electrochemical cell is a device that produces an electric current from chemical reactions occuring within it.

Electrochemical cells have two electrodes; the anode and the cathode. The anode is defined as the electrode where oxidation occurs while the cathode is the electrode where reduction occurs.

The voltaic cell uses two different metal electrodes each immersed in an electrolyte solution. The two electrodes are connected to each other by means of a wire which allows the flow of electrons from the anode to the cathode. The electrolytes are connected by means of a salt bridge which is a junction that connects the electrolytic solution in the anode and cathode compartment. The salt bridge usually consists of a strong electrolyte like NaCl, KCl, Na₂SO₄, etc.

The electrolyte in the salt bridge serves two purposes: it completes the circuit by providing a path for electron flow and it maintains electrical neutrality in both solutions by allowing ions to migrate between them.

As the reaction proceeds in the given voltaic cell above, the Na₂SO₄ present in the salt bridge will dissociate into Na⁺ and SO₄²⁻ ions. As the copper ions in the solution are being deposited on the copper cathode as neutral copper atoms, the solution will become more negative, therefore the Na⁺ ions in the salt bridge will migrate into the the solution in order to maintain electrical neutrality. Also, at the anode, as the Mg metal dissolve into the solution as Mg⁺² ions, the  solution will tend to become more positive. Therefore, the SO₄²⁻ ions present in the salt bridge will migrate into the solution in order to maintain electrical neutrality.