Chem 4300 Conductivity Conductance G = 1/R, expressed in W-1(mho) or S (siemens) where 1 W-1 = 1 S Conductance is a extensive property, the intensive version is conductivity, k k = G * l / A where l = distance between electrodes and          A = area of electrodes Experimentally we will just convert l/A to a cell constant so k = k G = k / R k is just determined by the measurement of the conductance or resistance of a solution for which the conductivity is known, generally a KCl solution. The units of specific conductivity (k) are generally in W-1 cm-1 the units of the constant k are in cm-1. Since we are working in a solution of some concentration we make one further conversion to either molar conductivity (Lm) or equivalent conductivity (L) Lm = k/c and L = k/n where c = molar concentration (in units of mol/cm3) and           n = equivalent concentration (in units of equiv./cm3) Kohlrausch's Law relates the variation of molar conductivity with concentration for strong electrolytes. Lm = Lom - K c1/2 where K = is a constant that is dependent on solvent and electrolyte            Lom = the limiting molar conductivity            c = molar concentration Limiting molar conductivity (Lom) and Kohlrausch's constant (K) can be obtained from a fit of molar conductivity (Lm) versus the square root of concentration (c1/2) Kohlrausch also noted that the limiting conductivity of a salt in solution was related to the limiting conductivity of the ions according to the following equation Lom = n+ l+ + n- l- where l's are the conductivity of the ions and n's are the number of ions For weak electrolytes conductivity data can be used to calculate the fraction dissociated (a) a = Lm/Lom so for a 1:1 weak electrolyte Kd = c a2 /[(1 - a) co] = c(Lm/Lom)2/[(1 - Lm/Lom) co] linearizing 1/Lm = 1/Lom + (Lm c)/[Kd (Lom)2] so fit 1/Lm vs (Lm * c) your intercept, b = 1/Lom or Lom = 1/b and you slope, m = 1/[Kd (Lom)2] or Kd = b2/m 