MOLAR CONDUCTIVITY AT INFINITE DILUTION OF ELECTROLYTES LAB REPORT

OBJECTIVETo determine the molar conductivity at infinite dilution (Ʌ0) of sodium chloride, hydrochloric acid, sodium acetate, and acetic acid at 250c. INTRODUCTION Electrolytes are substances which dissolve in water to produce solutions which conduct electrical current. Such substances produce ions when dissolve in water, and the ions carry the current through solution. Nonelectrolytes are the substances whose aqueous solution do not contain ions and hence do not conduct electrical current. Electrolytes are classified as either strong electrolytes or weak electrolytes. Strong electrolytes when dissolved in water ionize completely to produce ions. For example, when NaCl is dissolved in water: NaCl (s) → Na+ (aq) + Cl- (aq) There are no dissolved NaCl molecule present in the solution. Solutions of strong electrolytes are good conductor of electricity because they contain a relatively high concentration of ions. Strong Electrolytes The electrolytic conductivity (K) (S cm-1) of a solution increases with concentration. However, quantity K is not a suitable quantity for comparing the conductivities of different solutions. If a solution of one electrolyte is much more concentrated than another, it may have a higher conductivity simply because it contains more ions. Instead, molar conductivity (Ʌ) (S cm-1) should be adopted for comparison. It is defined as (K/concentration). Quantity Ʌ decreases as the concentration increases. Onsager showed theoretically for strong electrolytes in dilute solution that the effect of ionic attraction reduces the molar conductivity as in Eq. (1) Ʌ = Ʌ0 - K√c (1) Quantities c and Ʌ0 denote concentration of the electrolyte of the molar conductivity at in finite dilution. Below concentrations of about 0.1 M, a plot of Ʌ against √c result in a straight line . The intersection of this line with the ordinate is the Ʌ0. The Ʌ0 values are found to be additive. Kohlrausch assumed that in such a system the molar conductivity at infinite dilution is simply the sum of the independent contribution of the ions. . HCl 3) 0.1 M sodium acetate. when ion-ion interactions are at a minimum that the law strictly holds. NaCl 2) 0. CHEMICALS 1) 0. NaAc APPARATUS 1) Digital conductivity meter (1) 2) 100 mL volumetric flask (18) 3) 50 mL burette (3) 4) 100 mL beaker (9) 5) Magnetic stirrer with stirring bar (1) 6) Conductivity probe holder (1) PROCEDURES 1) A clean burette was filled with 0.1 M hydrochloric acid. This equation has been written for infinite dilution since it only under such conditions.Consider a strong electrolytes that yields ions A and B solution: ApBq → pAz+ + qBzKohlrausch’s law of independent migration of ions proposed: Ʌ0 = pƛ0+ + qƛ0For a 1-1 electrolyte A+BɅ0 = ƛ0+ + ƛ0(3) (2) Quantity ƛ0 denotes molar ionic conductivity at infinite dilution. (S cm2 mol-1).1 M NaCl solution.1 M sodium chloride. It is the applicable to both strong and weak electrolytes. 0005 and 0.  NaCl  Concentration = 0.05.001. quantities of K was corrected as (K-Kwater). 0. NaAc) 0n the same graph paper. 0. If the K values of the solutions are comparable to the DI water.0001 M.88 mS cm-1 at 250c.2) The required volume of 0. 3) The digital conductivity meter was calibrated with conductivity standard of 1413 μS cm -1 or 12. Probe was support with probe holder.005.01. 5) The beaker was filled with 50 mL deionized water and stirring bar was placed in. The NaCl solution was begin with the lowest concentration first.0001 M Λ (S cm2 mol-1) = . 7) The probe was immersed to a depth approximately 5 cm in the solution. RESULTS AND DISCUSSIONS 1) Tabulate the results.  Refer to the appendix 2) Determine the Ʌ (S cm2 mol-1) for each of the strong electrolyte solutions. then plot Ʌ versus √c (unit of c in mol cm-3). 4) Stirring bar and conductivity probe was rinsed by using DI water. 0. 8) The magnetic stirrer was switch on and the electrolytic conductivity (K) of the DI water at 250c was recorded. You may include all the three plots (NaCl. 6) The beaker was placed on the magnetic stirrer. 0. 9) Steps 4-8 were repeated with the diluted NaCl. 11) All electrolytic conductivity measurements was measured at 250c.1 M NaCl was drained out into each volumetric flask and top up with DI water to prepared the following molarities. 0. HCl. 10) Steps 1-9 by using HCl and NaAc solutions. 1 S cm2 mol-1  Concentration = 0.001 M Λ (S cm2 mol-1) = = ( ) [ ] = 168.8 S cm2 mol-1  Concentration = 0.005 M Λ (S cm2 mol-1) = .= ( ) [ ] = 509 S cm2 mol-1  Concentration = 0.0005 M Λ (S cm2 mol-1) = = ( ) [ ] = 207. 0001 M .2 S cm2 mol-1  Concentration = 0.05 M Λ (S cm2 mol-1) = = ( ) [ ] = 114.= ( ) [ ] = 127 S cm2 mol-1  Concentration = 0.2 S cm2 mol-1  HCl  Concentration = 0.01 M Λ (S cm2 mol-1) = = ( ) [ ] = 123. Λ (S cm2 mol-1) = = ( ) [ ] = 1995 S cm2 mol-1  Concentration = 0.001 M Λ (S cm2 mol-1) = = ( ) [ ] = 423 S cm2 mol-1 .0005 M Λ (S cm2 mol-1) = = ( ) [ ] = 430 S cm2 mol-1  Concentration = 0. 05 M Λ (S cm2 mol-1) = = ( ) [ ] = 394.005 M Λ (S cm2 mol-1) = = ( ) [ ] = 418 S cm2 mol-1  Concentration = 0.01 M Λ (S cm2 mol-1) = = ( ) [ ] = 412 S cm2 mol-1  Concentration = 0.6 S cm2 mol-1 . Concentration = 0. 001 M Λ (S cm2 mol-1) = = ( ) [ ] . NaAc  Concentration = 0.0001 M Λ (S cm2 mol-1) = = ( ) [ ] = 371 S cm2 mol-1  Concentration = 0.0005 M Λ (S cm2 mol-1) = = ( ) [ ] = 144.4 S cm2 mol-1  Concentration = 0. 005 M Λ (S cm2 mol-1) = = ( ) [ ] = 92.05 M Λ (S cm2 mol-1) = = ( ) [ ] .2 S cm2 mol-1  Concentration = 0.= 128 S cm2 mol-1  Concentration = 0.7 S cm2 mol-1  Concentration = 0.01 M Λ (S cm2 mol-1) = = ( ) [ ] = 85. 2 3.= 84.2361 x 10 -4 -3 -3 Ʌ (S cm2 mol-1) HCl 1995 430 423 418 412 394.1623 x 10-4 7.005 0.8 509 207.1 127 123.2 85. determine the value of Ʌ0 for each of the solution.0000 x 10 2.1623 x 10-3 7.0 M concentration.4 128 92. The value of Ʌ 0 for each solution were determined by extended the straight line to the 0.7 84.001 0.8 168.05 3. .0712 x 10-3  Graph of Ʌ versus √c  Refer to the appendix 3) From the linear regressions.0005 0.8 S cm2 mol-1  Table of Ʌ versus √c c (mol L-1) √c (mol cm-3) NaCl 0.6 NaAc 371 144.0712 x 10 1.  From the graph:  Ʌ0 (NaCl) = 230 S cm2 mol-1  Ʌ0 (HCl) = 475 S cm2 mol-1  Ʌ0 (NaAc) = 100 S cm2 mol-1  The value of slope for the graph of Ʌ versus √c are negative.01 0.2 114.0001 0.  Molar conductivities of weak electrolytes.Λmo can be easily calculated with the help of Kohlrausch's law.+ λ0Na+ Ʌ0HCl = λ0H+ + λ0ClɅ0NaCl = λ0Na+ + λ0ClTherefore: Ʌ0CH3COOH = Ʌ0CH3COONa + Ʌ0HCl .Ʌ0NaCl . determine the value of Ʌ0 for acetic acid (HAc). 5) From the Ʌ0 value.+ λ0H+ Ʌ0CH3COONa = λ0CH3COO.4) Report the standard errors in the Ʌ0.    Ʌ0 (NaCl) = 230 S cm2 mol-1 Ʌ0 (HCl) = 475 S cm2 mol-1 Ʌ0 (NaAc) = 100 S cm2 mol-1 Ʌ0CH3COOH = λ0CH3COO.  The equivalent conductivity of weak electrolytes increases steeply at very low concentrations (see the above graph) and hence their limiting values (Λo) cannot be determined by extrapolating the Λc to zero concentration. 4 76. HCl.6 38.11 + 76.4 40.34 = 126.34 78.34 = 425.9 = 349.6 + 76.69 50.50 106.45 S cm2 mol-1 .94 S cm2 mol-1  NaCl Ʌ0NaCl = λ0Na+ + λ0Cl= 50.11 73. NaAc and HAc.1 76. Cations H+ Li+ Na+ K+ Mg2+ Ca2+ Ba2+  HCl Ʌ0HCl = λ0H+ + λ0Cl- λ+0 /S cm2mol-1 349.28 anions OHClBrISO42NO3CH3COO- λ-0 /S cm2mol-1 199.12 119.00 127.8 159.6 71.= (100 + 475 – 230) S cm2 mol-1 = 345 S cm2 mol-1 6) Using the table of molar ionic conductivities of electrolyte at in finite dilution in aqueous solution at 250c find the Ʌ0 of NaCl. 9 + 50.5 S cm2 mol-1 7) Compare Ʌ0.6 = 390.89% % error (HCl) = x 100 = x 100 .01 S cm2 mol-1  HAc Ʌ0CH3COOH = λ0CH3COO. Describe possible sources for systematic errors and degree of their importance.theory determined from the standard data.exp with the Ʌ0.11 = 91.+ λ0H+ = 40.+ λ0Na+ = 40. NaAc Ʌ0CH3COONa = λ0CH3COO.9 + 349. % error (NaCl) = x 100 = x 100 = 81. REFERENCES 1) http://www.88%  Possible factor that affect the errors:  Interionic attractions: depends on solute-solute interactions.51% % error (NaAc) = x 100 = x 100 = 9.com/physical/electrochemistry/kohlrausch/kohlrausch-law.  Temperature: Electrolytic conduction increase with increase in temp.adichemistry.htm .  Concentration of solution: Higher concentration of solution less is conduction.html 2) http://en. If weak electrolyte. for HCl is 475 S cm2 mol-1.  Viscosity solvent: depends upon solvent-solvent interactions.jesuitnola. for NaAc is 100 S cm2 mol-1 and for HAc is 345 S cm2 mol-1.org/upload/clark/labs/PerError. CONCLUSION From the experiment.= 11.  Solvation of ions: depends on solute-solvent interactions.wikipedia. ionization is less & if strong electrolyte. the value of Ʌ0 at 250c for NaCl is 230 S cm2 mol-1.org/wiki/Conductivity_%28electrolytic%29 3) http://www.