The Construction of Simple Voltaic Cells

It maintains the electrical neutrality in each half-cell as ions flow into and out of the salt bridge. 

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Describe the construction of simple voltaic cells from half-cells and a salt bridge, and understand the function of each component... 

Counting Electrons Coulometry and Faraday s Law of Electrolysis 21-7 Commercial Applications of Electrolytic Cells Voltaic or Galvanic Cells 21-8 The Construction of Simple Voltaic Cells... 

A simple voltaic cell, known as the Daniell cell (Figure 9.39), can be constructed by placing a zinc electrode in a solution of zinc sulfate and a copper electrode in a solution of copper(ii) sulfate. The two electrodes are connected via wires and a high-resistance voltmeter. This is known as the external circuit and allows electrons to flow. This is a spontaneous process and no external energy source is required. The circuit is completed by a salt bridge which allows ions to flow in order to maintain electrical neutrality (Chapter 19). A simple salt bridge consists of a filter paper soaked in saturated potassium nitrate. Potassium and nitrate ions are chosen because they will not react with the other ions in solution or with the electrodes. 

Electricity interacts with matter because electrons are part of matter and form the chemical bonds. When electrons are transferred from one molecule to the other we call it a redox reaction. Since electric current is the movement of electrons, micro electric currents then exist in the solution where redox reactions take place. If all these micro-currents were made to flow in one direction we should be able to measure them as one macro electric current. Batteries (which are also called galvanic cells or voltaic piles ) are devices which do exactly this they produce electric current by making redox reactions take place at electrodes, i.e. at the metal solution boundary. The metal can be either the source or the sink for electrons. Thus electric current is made to flow from the metal into the solution or from the solution into the metal. Can one do the reverse Can one induce redox reactions by passing through the solution current from a source The answer is definitely yes . The instrument by which such changes are produced is an electrolytic cell . A simple cell can be constructed from two pieces of dissimilar metals dipping into a solution of some electrolyte in a beaker. The metal pieces are now the electrodes. This book is concerned with chemical reactions produced by electric current or electric current produced by chemical reactions at electrodes. It is concerned with redox reactions in cells. 

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