Electron, Electricity and Electrochemistry.pptx

This Units deals with the effects of electricity on the Chemistry of substances.

1. By: KAMAGA rasuli

2. Electrolysis And Electrochemistry Electrolytic Conductivity And Molar Conductivity

3. Factors affecting electrolytic conductivity of a solution The factors include: Temperature Concentration

4. The effect of the above factors depends on the nature of the electrolyte i.e. strong or Weak in nature.

5. Temperature For strong electrolytes, increase in temperature increase electrolytic conductivity, Why ? As temperature increases , the average kinetic energy of the conducting ions increases . The viscosity of the water decreases and the ionic mobility increases

6. Temperature For weak electrolytes, the effect depends on enthalpy changes accompanied with ionization of the weak electrolytes i.e. gives out heat ( Exothermic ) or absorbs heat ( Endothermic )

7. Temperature For a weak electrolyte that ionizes exothermically , increase in temperature decreases the degree of dissociation according to Le Chatelier’s principle, decreasing the number of conducting ions per unit volume of solution thus decreasing the electrolytic conductivity

8. Temperature For a weak electrolyte that ionizes endothermically , increase in temperature increases the degree of dissociation according to Le Chatelier’s principle , increasing the number of conducting ions per unit volume of solution thus increasing the electrolytic conductivity.

9. Molar Conductivity

10. Factors affecting Molar Conductivity Temperature of the solution Magnitude of the charge on the ions Ionic radius Viscosity of the solvent Concentration of the solution Temperature

11. 1.Temperature of solution For strong electrolytes molar conductivity increases with increase in temperature Explanation Increase in temperature increases the average kinetic energy of conducting ions, decreasing the viscosity of water, increasing the ionic mobility.

12. 1.Temperature of solution For weak electrolytes the effect of temperature depends on the enthalpy change accompanying ionization of the electrolyte. For weak electrolyte that ionizes exothermically , increase in temperature decreases the degree of ionization according to Le Chatelier’s principle, decreasing the number of conducting ions per unit volume, thus decreasing the molar conductivity

13. 1.Temperature of solution For a weak electrolyte that ionizes endothermically , increase in temperature increases the degree of dissociation according to Le Chatelier’s principle, increasing the number of conducting ions per unit volume of solution thus increasing the molar conductivity .

14. Trial Question Distinguish between electrolytic conductivity and molar conductivity The molar conductivity of ethanoic acid containing is 8.50 units at 18 and 14.7 units at 100 . Explain the difference in molar conductivities at the two temperatures .

15. 2. Magnitude of the charge on the ions Molar conductivity increases with increase in the magnitude of ionic charge. Why? Ions with high charges are more strongly attracted by the oppositely charged electrode and move faster.

16. 3. Ionic radius Molar conductivity increases with increase in ionic radius. The higher the ionic radius, the lower the charge density and the less hydrated the ion. The less hydrated ions move more faster than heavily hydrated ions hence ions with smaller ionic radius are more conducting than ions with higher ionic radius

17. Trial Questions Explain why the: (a) magnesium ion has a higher molar conductivity than the sodium ion (b) sulphate ion has a higher molar conductivity than the chloride ion. (c) the molar conductivity of the lithium ion is smaller than that of the sodium ion.

18. 4. Viscosity of the solvent The higher the viscosity of the solvent, the lower the ionic mobility hence the lower the molar conductivity

19. 5. Concentration of the solution The sketches below show the variation of molar conductivity with the square root of concentration for both a strong electrolyte and a weak electrolyte

20. Explanation of the shapes of the graphs For potassium chloride (strong electrolyte), increase in concentration, decreases molar conductivity. WHY ? Increase in concentration increases the total number of conducting ions per unit volume, decreasing inter ionic distance, increasing ionic interference decreasing ionic mobility.

21. Explanation of the shapes of the graphs At zero concentration (infinite dilution), molar conductivity reaches a maximum value called molar conductivity at infinite dilution because ionic interference is negligible

22. Explanation of the shapes of the graphs Note : Molar conductivity at infinite dilution is obtained from the graph by extrapolation .

23. Explanation of the shapes of the graphs For Ethanoic acid (Weak electrolyte), Increase in concentration decreases molar conductivity. WHY? Being a weak electrolyte, Increase in concentration decreases the degree of dissociation decreasing the number of conducting ions per unit volume of solution. Instead of concentration, reciprocal of concentration( ), also called dilution can be used.  

24. 5. Concentration of the solution The sketches below show the variation of molar conductivity with the dilution for both a strong electrolyte and a weak electrolyte.

25. Explanation of the shapes of the graphs For potassium chloride (Strong electrolyte), Increase in dilution increases molar conductivity to a maximum value at which it remains constant at infinite dilution . WHY? Increase in dilution increases inter-ionic distance decreasing ionic interference, increasing ionic mobility.

26. Note : At zero concentration ( infinite dilution ), the ionic interference is negligible . Molar conductivity at infinite dilution is obtained from the graph by extrapolation .

27. Explanation of the shapes of the graphs For Ethanoic acid (Weak electrolyte), Increase in dilution increases molar conductivity. WHY? B eing a weak electrolyte, Increase in dilution increases degree of dissociation increasing the number of conducting ions per unit volume of solution.

28. Graphs NOTE : 1. Neither the graph of molar conductivity against concentration nor those against dilution begin from the origin. 2. The graphs DO NOT coincide anywhere too.

29. Trial Questions The table below shows values of molar conductivity of ethanoic and potassium chloride at different concentrations. Concentration (moldm -3 ) 0.0001 0.001 0.01 0.1 1 2 3 129.1 127.3 122.4 112.0 98.3 92.6 88.3 107.0 41.0 14.3 4.6 1.32 0.80 0.54 Concentration (moldm -3 ) 0.0001 0.001 0.01 0.1 1 2 3 129.1 127.3 122.4 112.0 98.3 92.6 88.3 107.0 41.0 14.3 4.6 1.32 0.80 0.54

30. (a). On the same axes, plot graphs for molar conductivity against the square root of concentration. (b). State and explain the shapes of the graphs in (a) above.

31. UNEB QUESTION BANK For more Questions, Kindly Check: 1. 2006/P1/No.11 2. 2005/P2/No.4 3. 1996/P1/No.15 And more,

32. KOHLRAUSCH’S LAW OF INDEPENDENT MIGRATION OF IONS AND ITS APPLICATION.

33. KOHLRAUSCH’S LAW OF INDEPENDENT MIGRATION OF IONS Kohlrausch Friedrich investigated the molar conductivity at infinite dilution of a large number of strong electrolytes, found that it was a sum of two quantities i.e. anion and cation Today the terms are called “ molar conductivities of ions

34. KOHLRAUSCH’S LAW OF INDEPENDENT MIGRATION OF IONS States that “the molar conductivity at infinite dilution of an electrolyte is equal to the sum of the molar conductivities at infinite dilution of the ions produced by the electrolyte” i.e. For Sodium Chloride (NaCl) + = +  

35. KOHLRAUSCH’S LAW OF INDEPENDENT MIGRATION OF IONS For Sodium sulphate, (Na 2 SO 4 ) For Aluminum Sulphate (Al 2 (SO 4 ) 3 ) = + 3 For ethanoic acid (CH 3 COOH) =  

36. APPLICATION OF KOHLRAUSCH’S LAW Indirect determination of molar conductivity at infinite dilution for weak electrolyte, Determine solubility of sparingly soluble electrolytes, Determine solubility product of sparingly soluble electrolyte, Determine the degree of dissociation and equilibrium constants of weak electrolyte.

37. D etermination of molar conductivity at infinite dilution for weak electrolyte

38. Infinite dilution The concept of  infinite dilution  is used in the chemistry to analyze the substance's dissolution nature in solvents.   Infinite dilution  is a hypothetical state of the solution where solute concentration is considered to be zero .

39. Molar conductivity at infinite dilution Also called “limiting molar conductivity” Can be obtained if the molar conductivities of selected strong electrolyte are known. For instance:

40. Example #1 For instance; For ethanoic acid, molar conductivity at infinite dilution can be obtained from the molar conductivities at infinite dilution of HCl, CH 3 COOK and KCl. …………………….( i ) ….(ii)  

41. ………………….( iii ) ….( iv ) Equation ( iv ) can be obtained by adding ( ii ) and (iii) and subtracting equation ( i ) )=[ )]  

42. Cont’d ( (HCl)- (KCl) Given the molar conductivities at infinite dilution of some electrolytes are as shown below.   Compound ( Sodium chloride 113.0 Ammonium chloride 134.1 Sodium hydroxide 225.2 Sodium ethanoate 101.2 Hydrochloric 397.8 Compound Sodium chloride 113.0 Ammonium chloride 134.1 Sodium hydroxide 225.2 Sodium ethanoate 101.2 Hydrochloric 397.8

43. Cont’d (a). Calculate the molar conductivity at infinite dilution of: ( i ). Methanoic acid ( ). = (101.2+397.8-113.0) Scm 2 mol -1 = 386 Scm 2 mol -1  

44. Cont’d (ii). Ammonia solution . = (134.1+225.2-113.0) Scm 2 mol -1 = 246.3 Scm 2 mol -1  

45. Cont’d (iii). Ammonium methanoate (HCOONH 4 ). = (101.2+134.1-113.0) Scm 2 mol -1 = 122.3 Scm 2 mol -1  

46. Cont’d (b). Explain the difference in your answers in a( i ) and (iii) above. The molar conductivity at infinite dilution of methanoic acid is higher than that of ammonium methanoate because the H + ion in methanoic acid has a higher molar conductivity than the ammonium ion in ammonium methanoate .

47. Example #2 The molar conductivity at infinite dilution of the sulphate ions is 160 Scm 2 mol -1 . if the molar conductivity at infinite dilution of Aluminium sulphate is 858 Scm 2 mol -1 . Calculate the molar conductivity at infinite dilution of Aluminium ions.

48. Example #2 858 = + 3(160) = 858-480 = 378 = = 189  

49. UNEB 1995/P1/No.15 (a) ( i ). ( i ). State the Kohlrausch’s law of Ionic conductivity at infinite dilution. (ii). Calculate the molar conductivity of methanoic acid at infinite dilution. ( =9.50x10 -2 Scm 2 mol -1 ; =1.26x10 -1 Scm 2 mol -1 ; x10 -1 Scm 2 mol -1 ).  

50. Solution = = ( 9.50x10 -2 ) +(4.26x10 -1 )-(1.26x10 -1 ) Scm 2 mol -1 =(0.521-0.126) Scm 2 mol -1 = 0.395 Scm 2 mol -1  The molar conductivity at infinite dilution is 0.395 Scm 2 mol -1  

51. UNEB QUESTION BANK 1996/P1/No.15 (c) 1999/P1/13 (b) 2004/P1/No.12 2004/P2/No.2 (b) 2006/P1/No.11 (c) 2007/P1/No. 17 (b) And many more.

52. Application No.#2 Determination of solubility and solubility product of sparingly soluble electrolytes.

53. Thanks