Conductometry

Conductometry is a method used to analyse ionic species and observe chemical reactions by determining the electrolytic conductivity of the reaction mixture or products. The process of conductometry is  quite prominent in the field of analytical chemistry. Conductivity can be measured either directly with a conductivity metre or indirectly through the analytical procedure of conductometric titration.

Conductometry is commonly employed in analytical chemistry, with conductometric titration being a typical technique. In analytical chemistry, the word conductometry is often used interchangeably with conductometric titration. Conductometry is an extensively used technique for determining the total conductance of a chemical solution or examining the ion titration process’s endpoint.

The practice of conductometry on electrolytes goes way back to the 18th century, Andreas Baumgartner being the first to notice that salt and mineral water conducts electricity.  The analytical process of conductometry or in the vernacular term of analytical chemistry, conductometric titration was then further modified and developed by Friedrich Kohlrausch in the 1860s. Kohlrausch began his further understanding in conductometry when he subjected water, acids and other chemical solutions to alternating current. The experiments conducted by Kohlrausch were able to answer the question “What is conductometry?”. The effective technique of conductometry was earlier used to test the purity of water. One of the present applications of conductometry is testing the efficiency of water purifiers. 

Theory and Principle of Conductometry

The principle of conductometry is based on the fact that throughout the titration, one of the ions is replaced by the other, and these two ions usually differ in their ionic conductivity, causing the conductivity of the solution to vary during the titration. Movement of ions in an electrolytic solution is highly dependent on the concentration of the ions. The equivalence point in the process of conductometry is the phase at which the conductivity of the electrolytic solutions undergoes a sudden variation. Most common changes in the conductance are associated and dependent on the varying concentrations of the conducting ions. The fundamental benefits of conductometry are its applicability to very dilute and colourful solutions, as well as systems with relatively incomplete reactions.

By displaying the variation in conductance as a factor of the volume of titrant, the equivalence point may be identified visually. There are some rules stated under the principle of conductometry which are utilised to alleviate the errors while producing the conductance data, because even a small error can cause a large deviation. 

Movement of ions in an electric field

The resulting data will be more accurate if the ion that replaces the reactive ion has a lower conductivity. For example, titrating a silver salt using lithium chloride rather than HCl is optimal. Because these ions have poor conductivity, cations are often titrated with lithium salts and anions with acetates. 

The principle of conductometry is precisely based and backed up by Ohm’s law which states that current I is directly proportional to Electromotive force or emf E and inversely proportional to the resistance R of the conductor. The formula is given by-

  I = E/R

The reciprocal of resistance is known as conductance. As given in the equations below-

The formula of resistance in terms of length, area of cross section and resistivity is given by-                                 

  R = ρl/a

A solution’s electrical conductance is a measurement of its current carrying capability and is thus governed by its overall ionic strength. Conductance of a solution is its non-specific property.

Conductance C is inversely proportional to Resistance R, thus the formula for conductance in terms of length, area of cross section and conductivity K is the exact reciprocal of the formula for resistance.

   C = 1/R

     =a/kl

Comparing both the formulae we reach the conclusion that Conductivity K is also inversely proportional to resistivity ρ. 

Applications of conductometry 

The main application of conductometry is in the branch of chemical kinetics, which includes determining and measuring the rate of reactant used and rate of the product formed in the reaction.

Acid-Base titration is one of the most used applications of conductometry especially at minimal concentrations. Because conductance is a non-specific property, direct conductance measurements are useless unless the solution contains just the electrolyte to be evaluated or the concentrations of remaining ionic species in the solution are known.               

Conductometric titration is used to monitor water contamination and alkalinity in both stagnant and flowing water bodies. Conductometry is applied in chemical analytics to determine the rate of solubility in sparingly soluble salts. 

Conclusion

Conductometric titration is a method of continually measuring the electrolytic conductivity of a reaction mixture when one reactant is introduced through a burette. It is also used to determine the concentration of the chemical substance to be tested, which is referred to as an analyte. In analytical chemistry, conductometric titration is sometimes used interchangeably with the word conductometry. Conductometry is used to determine the total conductance of any solution or to examine the endpoint of ion titrations. The principle of conductometry is significant and is typically used on coloured and turbid solutions.