# lab 9 - EXPERIMENT 9 CONDUCTOMETRIC TITRATIONS 07F...

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EXPERIMENT 9 CONDUCTOMETRIC TITRATIONS 07F Measurement of the conductivity of a solution (generally aqueous) is perhaps the easiest way to determine whether the compound is a strong electrolyte, a weak electrolyte, or a non- electrolyte. The conductivity (or conductance) of a solution, L , is defined as the reciprocal of the electrical resistance, R, the directly measured quantity: 1 , 1 = ohm R L The resistance of a solution is proportional to the distance between the electrodes, d , and inversely proportional to the size or cross sectional area of the electrodes, A . {Compare with the electrical resistance of wire.} In addition, the resistance of a solution depends on the concentrations of charge carriers in the solution and how fast they move in solution in an applied electric field (voltage difference). For a solution, the following equations hold ρ κ 1 1 1 = = = = = d A d A R L A d R In this equation, ρ is the specific resistance of the solution (which depends on the concentrations and types of ions in solution and not the experimental apparatus) and κ is the specific conductivity of the solution, which is also a function of the solution and not the apparatus. For aqueous solutions of electrolytes, the specific conductivity (conductance) of the solution, κ , increases with increasing concentration of ions in solution, and is very nearly proportional to the concentration of ions (for low to moderate concentrations), as shown in the figure below. Conductivity vs. Concentration y = 384.29x y = 213.18x y = 103.6x 0 10 20 30 40 50 60 70 80 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 Normality, Eq/L Specific Conductivity, 10 -3 ohm -1 HCl NaOH NaCl Linear (HCl) Linear (NaOH) Linear (NaCl) The plots above (data from International Critical Tables) show a nearly linear increase in specific conductivity with increasing concentration for HCl, NaOH, and NaCl. However, the 1

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## This note was uploaded on 04/13/2008 for the course CHEM 119H taught by Professor Munson during the Fall '07 term at University of Delaware.

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lab 9 - EXPERIMENT 9 CONDUCTOMETRIC TITRATIONS 07F...

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