1. Electric conductivity
Those substance which allow the electric current to pass through them are called electric conductors and property is called electric conductivity.
On the basis of Electric conductivity, substances are of two types -
1.1 Non-conductors :
Those substance which do not allow the electric current to pass through them are called nonconductors. eg. All covalent compounds & nonmetals.
1.2 Conductors :
Those substance which allow the electric current to pass through them are called conductors. eg. all metals, alloys, all acid and bases, salt and graphite etc.
On the basis of conducting units conductors are of two types -
1.2.1 Metallic or Electric Conductors :
Electricity conduct them due to the presence of free and mobile electron which act as electricity conducting unit called metallic or electric conductors. eg. Metals, Alloys, Graphite, Gas, Carbon etc.
1.2.2 Ionic Conductors or Electrolytes :
Conductors in which the current is passes through them due to the presence of free ions are called Ionic Conductors or Electrolyte or Electrolytic conductors.
Ionic conductors are further divided into two types on the basis of their strengths -
(a) Strong electrolytes :
(i) Those substance which are almost completely ionize into ions in their aqueous solution are called strong electrolytes.
(ii) Degree of ionisation for this type of electrolyte is one i.e. a ≈1. eg. HCl, H2SO4, NaCl.HNO3, KOH, NaOH, HNO3 , AgNO3, CuSO4, etc. Means all strong acids and bases and all types of salts.
(b) Weak electrolytes :
(i) Those substance which are ionize to a small extent in their aqueous solution are known weak electrolytes.eg. H2O, CH3COOH, NH4OH, HCN, HCOOH, Liq. SO2etc. Means all weak acids and bases.
(ii) Degree of ionization for this types of electrolytes in a <<< 1.
Arrhenius theory of Electrolytic Dissociation or Ionization
(a) When an electrolyte dissociates into water, it gives two types of charged particles called ions.
(b) Ions which carry ( ) ve charge and move towards cathode are called as `Cations' while ions carrying (-) ve charge and moving towards anode called as `anion'.
(c) Every electrolytic solution is always neutral in nature.
(d) Quantity or part of electrolyte which is ionized or decomposed or dissociate called as "Degree of Ionisation".
(e) Electrolyte which gives H ions after dissociation in the aqueous solution is called as acid while that which gives OH- after dissociation in the aqueous solution is called as base.
(f) Acidic strength of acids is directly proportional to the dissociation constant Ka.
pKa = - log Ka
Thus, Acidic strength
(g) Similarly basic strength of bases is directly proportional to Kb.
pKb = - log Kb
Basic strength of base α Kb α α pKa α
(h) Conductivity of solution depends upon the number of ions produced by the electrolyte, such as -
Conduction of solution µ number of ions produced by the electrolyte
(i) Solution of strong electrolyte has more electric conductivity property as compared to weak electrolyte.
(j) Only weak electrolyte followed the law of mass action and Ostwalds dilution law.
(k) When electricity passed through in the electrolytic solution, it gives only direction to movement of ions towards the electrodes.
(l) Movement of ions is inversely proportional to the molecular mass or atomic mass of ions.
Limitations of Arrhenius Concept :
(a) H+ and OH- ions exist as hydrated ions.
(b) He was unable to explain the acidic nature of CO2, SO2 etc. and basic nature of NH3, CaO, Na2CO3 etc.
(c) He could not explain the acid base reaction in the absence of water.
SO3(g) + CaO(s) ⇒ CaSO4(g)