Tiêu đề IONIC EQUILIBRIUM.pdf ✅

 Digital www.allendigital.in [ 149 ] Introduction The study of ionic reactions at equilibrium is known as ionic equilibrium According to Conductivity Substances are of two Types (1) Non-Conductor - Those substances which do not show the flow of current or electricity. Ex. Non - metals, plastics, rubber, wood etc. Exception – Graphite is a non-metal but shows conductivity due to motion of free electrons. (2) Conductors – Those substances which show conductivity or flow of current are called conductors and these are of two types: (a) Metallic conductors – Those conductors which show conductivity due to motion of free electrons. Ex. All metals (b) Ionic conductors – Those conductors which show conductivity due to movement of free ions. Ions are in free state in the solutions of ionic compounds. On passing electric current through the solution, ions move towards oppositely charged electrodes, i.e., the cation moves towards cathode (negative electrode) and the anion moves towards anode (positive electrode). Due to this reason, they are called as cations and anions respectively. The current flows through the solution due to the movement of the ion. According to Strength, Ionic Conductors Can be Classified as – (1) Strong electrolytes – Those ionic conductors which are almost completely ionized in aqueous solution are called as strong electrolytes. For strong electrolytes, the value of degree of ionisation is almost 100% i.e.  = 1 Ex. (2) Weak electrolytes – Those electrolytes which are partially ionized in aqueous solution are called as weak electrolytes. For weak electrolytes the value of  is less than one. Ex. 04 Ionic Equilibrium (a) All Strong Acids : H2SO4, HCl, HNO3, HClO4, HBr, HI (b) All Strong Bases : KOH, NaOH, Ba(OH)2, CsOH, RbOH (c) All Ionic Salts : NaCl, KCl, CuSO4 etc. (a) All Weak acids : HCN, CH3COOH, HCOOH, H2CO3, H3PO3, H3PO2, B(OH)3 or H3BO3, etc. (b) All Weak bases : NH4OH, Cu(OH)2, Zn(OH)2, Fe(OH)3, Al(OH)3 etc.
NEET : Chemistry [ 150 ] www.allendigital.in  Digital Arrhenius Concept (a) According to Arrhenius, when an electrolyte dissolves in water, it splits up into two oppositely charged particles i.e. cation and anion. (b) In an electrolytic solution (aqueous solution of electrolyte), total +ve charge = total –ve charge i.e. solution is electrically neutral. In an electrolytic solution number of +ve ions may or may not be equal to the number of negative ions. (c) Properties of an electrolytic solution are defined by its ions. Ex. Blue colour of CuSO4 solution is due to Cu+2 ions (dark blue colour) (d) When electric current is passed through aqueous solution of an electrolyte then cation shows migration towards cathode where as anion shows migration towards anode. (e) When a weak electolyte is dissolved in water an equilibrium is set up between unionized species and ionized species. This condition of the reversible ionic reaction is known as ionic equilibrium. AB (aq.)  A+ (aq.) + B– (aq.) Illustration 1: No. of total ions and resultant total charge in A2B3 electrolyte: (1) Five and + 1 (2) Five and – 1 (3) 0 and 0 (4) None of them Solution: (4) Illustration 2: Assertion: H2SO4 is a strong acid. Reason: H2SO4 is almost completely ionised in aqueous solution. (1) A (2) B (3) C (4) D Solution: (1) According to Law Of Mass Action. K = Ionisation Constant
Ionic Equilibrium  Digital www.allendigital.in [ 151 ] Ostwald's Dilution Law  Ostwald was the first to apply law of mass action to ionic equilibrium.  Ostwald dilution law is applicable only for weak electrolytes. Statement: dilution    At infinite dilution,  = 100% Thus, for weak electrolytes the degree of ionisation is directly proportional to square root of dilution or inversely proportional to square root of concentration. This law is known as Ostwald’s Dilution Law. ➢ At infinite dilution the value of  becomes equal to one. Application of Ostwald's Dilution Law: 2 K C=  According to Ostwald's dilution law when solution of a weak electrolyte is diluted then the degree of ionization of weak electrolyte is increases, and at infinite dilution it remains 100% dissociated. Let AB(aq) ⇌ A+ (aq) + B– (aq) Initial concentration C 0 0 At Equilibrium (C – C) (C) (C)  = Degree of Ionization (a) For mono basic weak acid (HA) (b) For mono acidic weak base (BOH) Application of Ostwald's Dilution Law According to Ostwald’s dilution law when solution of a weak electrolyte is diluted then the degree of ionization of weak electrolyte increases, and at infinite dilution it remains 100% dissociated.
NEET : Chemistry [ 152 ] www.allendigital.in  Digital (a) For mono basic weak acid (HA) (ii) [H+] (Concentration of H+) [H+] = C ........(1) Ka = C2 or  = Ka C .......(2) from Eq. (1) and (2) [H+] = C × Ka C [H+] = K C a  (iii)pH = –log [H+] put the value of [H+] pH = – log ( K C a  ) = – log (Ka × C)1/2 pH = – 1 2 [log Ka + log C] pH = – 1 2 log Ka – 1 2 log C pH = 1 2 pKa – 1 2 log C Summary: 1. Ka = C2 2. [H+] = C = K C a  3. pH = – log [H+] or pH = 1 2 pKa – 1 2 log C (b) For mono acidic weak base (BOH) Ionization constant (Ka) HA ⇌ H+ + A– Initial Concentration C 0 0 At equilibrium C – C C C  is Degree of Dissociation   <<<< 1  (1 –  ) ≈ 1  Ka = C2  (i) BOH ⇌ B+ + OH– Initial Concentration C 0 0 At equilibrium C – C C C   <<<< 1  (1 –  ) ≈ 1 Ionization constant (Kb)  is Degree of Dissociation  Kb = C2  (i)