Exp1 Corrosion

Objectives

1. To distinguish between galvanic and electrolytic cells.

2. To measure the relative reduction potentials for a number of redox couples in a galvanic cell.

3. To develop an understanding of the movement of electrons ,anions ,cations in a galvanic cell.

4. To identify the reactions occurring at the anode and cathode during the electrolysis of various aqueous salt solutions.

Introduction

A Galvanic cell consists of two half-cells. In its simplest form, each half-cell consists of a metal and a solution of a salt of the metal. The salt solution contains a cation of the metal and an anion to balance the charge on the cation. In essence, the half-cell contains the metal in two oxidation states and the chemical reaction in the half-cell is an oxidation-reduction (redox) reaction . In a galvanic cell one metal is able to reduce the cation of the other and, conversely, the other cation can oxidize the first metal. The two half-cells must be physically separated so that the solutions do not mix together. A salt bridge or porous plate is used to separate the two solutions yet keep the respective charges of the solutions from separating, which would stop the chemical reactions.The number of electrons transferred in both directions must be the same, so the two half-cells are combined to give the whole-cell electrochemical reaction.

Electrolytic cells is like galvanic cells, are composed of two half-cells ,one is a reduction half-cell, the other is an oxidation half-cell. Though the direction of electron flow in electrolytic cells may be reversed from the direction of spontaneous electron flow in galvanic cells, the definition of both cathode and anode remain the same .Reduction takes place at the cathode and oxidation occurs at the anode. When comparing a galvanic cell to its electrolytic counterpart, as is done in , occurs on the right-hand half-cell. Because the directions of both half-reactions have been reversed, the sign, but not the...