0.10 Electrochemistry and alchemy  (Page 7/5)

Electrochemistry and alchemy:

Molar mass of cu and turning cu into au

Objectives

• To learn Faraday’s two laws of electrolysis
• To relate an electric current to the passage of an amount of electric charge
• To discuss electrolysis in molten salts and in aqueous solutions
• To determine the molar mass of copper by electrodeposition from an aqueous solution
• To turn copper into “gold” (please bring a penny that is pre-1982 to lab with you)

Grading

You grade will be determined according to the following:

• Pre-lab (10%)
• Report Form (80%)
• TA evaluation of lab procedure (10%) which includes bringing a pre-1982 penny to lab

Before coming to lab …

• Read and complete the pre-lab
• Read the background information
• Read and be familiar with the Lab Instructions
• Find a pre-1982 penny and bring it with you to lab

 introduction  

Electrochemistry describes the interaction between electrical energy and chemical processes. Electricity continues to intrigue us, as it has since people first observed the sky shattered by bolts of lightning. Electrochemistry is of great practical value to contemporary living. Consider the number of batteries used for powering the many portable items of pleasure and need – everything from cassette recorders to hearing aids, from calculators to pacemakers. Pure metals are produced from natural ores, inorganic and organic compounds are synthesized, metal surfaces are plated with other metals or coated with paint to enhance their value and utility – all through electrochemistry.

Electricity is a moving stream of electrical charges. This flow, or electric current , can occur as electrons moving through a wire or as ions flowing through an aqueous solution. If the electrons lost and gained in a spontaneous reaction can flow through a wire on their pathway from the substance oxidized to the substance reduced, the energy of the reaction is released as electrical energy. Conversely, a non-spontaneous redox reaction can be driven forward by the introduction into the system of electrical energy from another source. Any device in which either process can occur is called an electrochemical cell.

There are two types of electrochemical cells. The first type generates electrical energy from a spontaneous redox reaction. These are called voltaic or galvanic cells , common household batteries are classic examples. An Italian physicist, Allesandro Volta in 1800 explained that electricity is generated by the connection of two dissimilar metals separated by any moist body (not necessarily organic). A simple voltaic cell, similar to that made by Volta, can be assembled using twelve pennies and twelve nickels (construct a column of alternating pennies and nickels with each coin separated by disk-size pieces of wet filter paper soaked in salt water).

In the second type of electrochemical cell, called an electrolytic cell, a non-spontaneous redox reaction is caused by the addition of electrical energy from a direct current source such as a generator or a storage battery. The process of generating a non-spontaneous redox reaction by means of electrical energy is called electrolysis.