Solutions . Calculate the potential of hydrogen electrode in contact with a solution whose pH is . . Calculate the emf of the cell in which the following reaction takes place: Ni(s) + 2Ag + ( .
M) ® Ni + ( . M) + 2Ag(s) Given that = . V . The cell in which the following reaction occurs: ( ) − → aq aq aq 2Fe 2I 2Fe I s has = .
V at K. Calculate the standard Gibbs energy and the equilibrium constant of the cell reaction. * Electronically conducting polymers – In MacDiarmid, Heeger and Shirakawa discovered that acetylene gas can be polymerised to produce a polymer, polyacetylene when exposed to vapours of iodine acquires metallic lustre and conductivity. Since then several organic conducting polymers have been made such as polyaniline, polypyrrole and polythiophene.
These organic polymers which have properties like metals, being composed wholly of elements like carbon, hydrogen and occasionally nitrogen, oxygen or sulphur, are much lighter than normal metals and can be used for making light-weight batteries. Besides, they have the mechanical properties of polymers such as flexibility so that one can make electronic devices such as transistors that can bend like a sheet of plastic. For the discovery of conducting polymers, MacDiarmid, Heeger and Shirakawa were awarded the Nobel Prize in Chemistry for the year . It can be seen from Table .
that the magnitude of conductivity varies a great deal and depends on the nature of the material. It also depends on the temperature and pressure at which the measurements are made. Materials are classified into conductors, insulators and semiconductors depending on the magnitude of their conductivity. Metals and their alloys have very large conductivity and are known as conductors.
Certain non-metals like carbon-black, graphite and some organic polymers * are also electronically conducting. Substances like glass, ceramics, etc., having very low conductivity are known as insulators. Substances like silicon, doped silicon and gallium arsenide having conductivity between conductors and insulators are called semiconductors and are important electronic materials. Certain materials called superconductors by definition have zero