CHM 2046C Module 14 Sample Name: __Answers_____

Part J: Chapter 17 Discussion Questions 10 points

1. Which electrode is the anode and which electrode is the cathode in an electrochemical cell?

The anode is the electrode at which the oxidation occurs. It is negative charged. The cathode is the electrode at which the reduction occurs. It is positive charged.

2. What is a salt bridge? Why is such a device necessary?

A salt bridge provides a means by which the electric circuit through an electrochemical cell can be completed without allowing the solutions in the two half cells to mix. The salt bridge contains a solution of an electrolyte-a salt. As metal ions are removed from the reduction half cell, they are balanced by the addition of cations or removal of the anions via the salt bridge. Cations move through the bridge from the anode to the cathode and anions move from cathode to anode.

3. What is the difference between a primary cell and a secondary cell?

A primary cell can not be recharged. Once the cell has reached equilibrium no farther electrical energy can be obtained. It is “Dead”.

A secondary cell can be recharged. Applying a reverse potential reverses the reaction.

4. What is the relationship between charge, potential, and energy?

Energy (J) = potential (V) x change (C)

5. What is the standard electrode? What is a standard electrode-reduction potential? Write the half cell reaction. What is its symbol?

The standard electrode, to which all other electrodes are compared, is the standard hydrogen electrode (SHE.). The hydrogen gas is at 1 Bar (1 atm) pressure and the concentration of acid is 1.0M. The SHE is assigned a half cell potential = zero

2 H₃O ¹⁺ (aq) + 2 e ^1- --à 2 H₂O (l) + 2 H₂ (g) Eo=0.00V

By convention, half cell potentials are always listed as standard reduction potentials.

The symbol is E^o. Cell potential is calculated by adding the half-cell potentials: E^o_cell = E^o_oxid + E^o_red