8 7. 1 Electrolyte and electrolytic solution Out-class reading Levine, pp. 294-310 Section 10.6 solutions of electrolytes Section 10.9 ionic association pp512515 Section 16.6 electrical conductivity of electrolyte solutions
§7.1 Electrolyte and electrolytic solution Out-class reading: Levine, pp. 294-310 Section 10.6 solutions of electrolytes Section 10.9 ionic association pp. 512-515 Section 16.6 electrical conductivity of electrolyte solutions
87.1 Electrolyte and electrolytic solution 5. Conducting mechanism of electrolyte Motion of ions in the solution: 1)diffusion: due to difference in concentration Electric transfer of ion in solution 2)convection: due to the difference in density under electric field 3)transfer/migration: due to the effect of How can current cross the electrode electric field solution interface
•Electric transfer of ion in solution under electric field + + + + + + + + − + Motion of ions in the solution: 1) diffusion: due to difference in concentration 2) convection: due to the difference in density 3) transfer/migration: due to the effect of How can current cross the electrode / electric field solution interface ? I E 5. Conducting mechanism of electrolyte §7.1 Electrolyte and electrolytic solution
87.1 Electrolyte and electrolytic solution CI At anode: At cathode 2CI→Cl2+2e-↑ 2H++2e→H2个 Conducting mechanism: 1) Transfer of ion in solution under electric field 2)electrochemical reaction at electrode/solution interface
Cl− e − e − e − At cathode: 2H+ + 2e− → H2 Cl− Cl− Cl− Cl− Cl− Cl− Cl− H+ e − H+ e − H+ e − H+ H+ H+ H+ H+ H+ Cl− At anode: 2Cl− → Cl2 + 2e− H+ Cl− Conducting mechanism: 1) Transfer of ion in solution under electric field; 2) electrochemical reaction at electrode/solution interface. §7.1 Electrolyte and electrolytic solution
87.1 Electrolyte and electrolytic solution 6. Law of electrolysis For quantitative electrolysis Number 110 2sM Faraday’sLaw where m is the mass of liberated matter; Q the electric coulomb, z the number of electron gained/lost during reactions, F a proportional factor named as Faraday constant, M the molar weight of the matter Faraday 's constant FARADAY DICCTISSION F=(16021917×1019×6022169×1023)Cmol-l= Micheal Faraday 96486. C mol- usually round off as 96500 C. mol-,is Great Britain 1791-1867 the charge carried by l mole of electron Invent the electric motor and generator and the principles of electrolysis
6. Law of electrolysis where m is the mass of liberated matter; Q the electric coulomb, z the number of electron gained/lost during reactions, F a proportional factor named as Faraday constant, M the molar weight of the matter. M zF Q m = For quantitative electrolysis: Micheal Faraday Great Britain 1791-1867 Invent the electric motor and generator, and the principles of electrolysis. Faraday’s Law Faraday’s constant F = (1.6021917 10-19 6.022169 1023 ) C·mol-1 = 96486.69 C·mol-1 usually round off as 96500 C·mol-1 , is the charge carried by 1 mole of electron. §7.1 Electrolyte and electrolytic solution
87.1 Electrolyte and electrolytic solution Current efficiency (n) Application of faraday's law 1)Definition of ampere: Q theoretical 77 effective 7 IUPAC. constant current that would effective theoretical deposit 0.0011180 g of silver per second from AgNO3 solution in one second: 1 Current efficiency is lower than 100% ampere due to side-reactions. For example, 2) Coulometer: copper /silver/gas(H2, 02) evolution of hydrogen occur during coulometer electro-deposition of copper 3)Electrolytic analysis -electroanalysis O← 4)Electrochemical capacitance
Current efficiency () effective theoretical Q Q = theoretical effective m m = Current efficiency is lower than 100% due to side-reactions. For example, evolution of hydrogen occur during electro-deposition of copper. 1) Definition of ampere: IUPAC: constant current that would deposit 0.0011180 g of silver per second from AgNO3 solution in one second: 1 ampere. Application of Faraday’s law 2) Coulometer: copper / silver / gas (H2 , O2 ) coulometer 3) Electrolytic analysis – electroanalysis Q ↔m ↔ n ↔ c §7.1 Electrolyte and electrolytic solution 4) Electrochemical capacitance
87.1 Electrolyte and electrolytic solution 7. Transfer of ion under electric field measure ionic mobility using moving boundary method How do we describe the motion of ions under electric field? MA. MA have an ion in common 1)Ionic mobility Rate of electric transfer: lonic velocity The boundary, rather different in color, BHB refractivity, etc. IS sharp de E V∝ A日A Ionic mobility(0): the ionic velocity CdcI per unit electric field, is a constant Cd tE
7. Transfer of ion under electric field 1) Ionic mobility d d E l d d E U l = Ionic mobility (U) : the ionic velocity per unit electric field, is a constant. Rate of electric transfer: Ionic velocity How do we describe the motion of ions under electric field? measure ionic mobility using moving boundary method MA, MA’ have an ion in common. The boundary, rather different in color, refractivity, etc. is sharp. x v t = v x U V tE l = = §7.1 Electrolyte and electrolytic solution
87.1 Electrolyte and electrolytic solution 8. Transference number Transference number(transfer/ transport number ), is the fraction of the current transported by an ion plane a Q=2++e O Q t+t=?
I = I＋ + I－ Q = Q＋ + Q－ j j j I Q t I Q = = t+ + t - = ? 8. Transference number Transference number (transfer/ transport number), is the fraction of the current transported by an ion. plane A I－ I＋ I + + + I Q t I Q = = - - - I Q t I Q = = §7.1 Electrolyte and electrolytic solution
87.1 Electrolyte and electrolytic solution 8. Transference number (1) Principle for measuring transference number C A B For time t: 0+ =AU+tC+Z+ F O=AUtC_Z_F Owing to electric migration, on the left side of plane a, there are more anions, while on the right side, more cations. Is this real?
For time t: Q+ = A U+ t c+ Z+ F Q − = A U− t c−Z−F (1) Principle for measuring transference number Owing to electric migration, on the left side of plane A, there are more anions, while on the right side, more cations. Is this real? A I＋ C B U t − 8. Transference number §7.1 Electrolyte and electrolytic solution
87.1 Electrolyte and electrolytic solution 8. Transference number (1) Principle of Hittorf method(1853) Example: Electrolysis of HCl ⊙④ SolutIon IF anodic region bulk solution cathodic region When 4 Faraday pass through the electrolytic cell 4CI-4e→ 3 mol H 3 mole 4I++4e 2C2个 I mol cl 2H final result For anodic region: residual reacted t C transfered anodic region bulk solution cathodic region
(1) Principle of Hittorf method (1853) Example: Electrolysis of HCl solution When 4 Faraday pass through the electrolytic cell anodic region bulk solution cathodic region + + + + + + + + + + + + + + + + + + − − − − − − − − − − − − − − − − − − + = 1 F + + + + + + + + + + + + + + + + + + − − − − − − − − − − − − − − − − − − 4Cl- -4e- → 2Cl2 4H+ +4e- → 2H2 3 mol H+→ 1 mol Cl- 3 mol H+→ 1 mol Cl- 8. Transference number anodic region bulk solution cathodic region + + + + + + + + + + + + + + − − − − − − − − − − − − − − final result For anodic region: residual initial reacted transfered c = c −c + c §7.1 Electrolyte and electrolytic solution
87.1 Electrolyte and electrolytic solution 8. Transference number EXAMPLE ④oo-lt Pt electrode FeCl solution 动( ock stopper In cathode compartment Initial: FeCl3 4.00 mol- dm Final FeCh, 3. 150 mol dm. FeCl,1.000 mol- dm Calculate the transference number of Fe3+ What factors will affect the accuracy of the Anode Cathode chamber chamber measurement? Hittorf's transference cell
EXAMPLE Pt electrode, FeCl3 solution: In cathode compartment: Initial: FeCl3 4.00 mol·dm-3 Final: FeCl3 3.150 mol·dm-3 FeCl2 1.000 mol·dm-3 Calculate the transference number of Fe3+ Hittorf’s transference cell Anode chamber Cathode chamber Cock stopper What factors will affect the accuracy of the measurement? 8. Transference number §7.1 Electrolyte and electrolytic solution
