255. Define the following terms: (i) Cathodic protection, (ii) Electrochemical series, (iii) Cell constant, (iv) Equivalent conductivity, (v) Strong and weak electrolytes.

(i) Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded sacrificial metal to act as the anode.
for example zinc is used to prevent iron
Zinc is more electro-positive than iron. Therefore, as long as zinc is there on the iron pipe, zinc acts as anode and the iron as cathode. As a result, rusting of iron is prevented.


(ii)Electrochemical series is a series of chemical elements arranged in order of their standard electrode potentials. The hydrogen electrode. H⁺(aq) + e^- →← 1/2H₂(g) is taken as having zero electrode potential. An electrode potential is, by definition, a reduction potential


(iii)The quantity 1/A is called cell constant denoted by the symbol. G*. It depends on the distance between the electrodes and their area of cross -section and has the dimension of length^-1 and can be calculated if l and A 
G* =l/A =Rk


(iv) A strong electrolyte is a solute that completely, or almost completely, ionizes or dissociates in a solution. While the specific conductance of a solution increases with concentration, the equivalent conductance decreases as the concentration increases. unit of equivalent conductance ${\mathrm{\Omega }}^{-1}{\mathrm{cm}}^{-2}{\mathrm{equi}}^{-1}$


(v)electrolytes :A substance that when dissolved in water produced a solution that can conduct electric current.
there are two electrolytes 
1. strong 
2.weak

strong Electrolytes conduct current very efficiently. Completely ionized or dissociate when dissolved in water
a. Soluble Ionic compounds
b. Strong acids (HNO3(aq), H2SO4(aq), HCl(aq))

HNO3--> H⁺ + NO^3-     (100% ionization)

c. Strong bases (KOH and  NaOH)

KOH -->K⁺    +OH ^-     (100% dissociation)

Weak electrolytes conduct only a small current
Slightly ionized in solution 
a. Weak acids (organic acids-->acetic, citric, butyric,malic, etc.)

                  HC₂H₃O₂  <==> H⁺  + C₂H₃O₂^-

b. Weak bases (ammonia)

                        NH₃ + H₂O <==> NH⁴⁺ + OH^-