Factors Affecting Variation of Conductivity

A liquid that conducts electricity is called an electrolyte. It contains ions that are formed due to the splitting of the compounds present in the liquid. Every electrolyte differs in its capacity to allow an electric current to pass through it.

The conduction of electricity forms the basis for a lot of phenomena that we observe in today’s world. Though primarily, the conduction of electricity is observed in solids, the same phenomenon in liquids plays a major role in many important technologies like batteries.

It is important to measure the capacity of electrolytes to transfer electricity. This value is measured by calculating the conductivity of the electrolytic solution. It is also important to understand how this conductivity changes with respect to different factors in the environment.

Conductivity

In physics, every material is considered to have a characteristic amount of resistance irrespective of what shape or size it is in. This characteristic resistance is termed the specific resistance of the material. The Greek letter, (rho) denotes resistivity.

Electricity is passed through a liquid when a special substance called an electrolyte is dissolved in it. Usually, electrolytes are dissolved in water to create an electrolytic solution. Applying voltage to an electrolytic solution causes electricity to pass through it, and it provides a certain resistance to this electricity.

By measuring the amount of resistance that an electrolytic solution provides to the passing current in it, and then by using Ohm’s law, we can calculate the specific conductance or conductivity of the electrolytic solution. Conductivity is usually measured in Siemens per metre. In the industries, a smaller unit called micro Siemens per metre is also used. 

The greek letter (kappa) is used to denote conductivity. The equation for conductivity can be found as 

According to Ohm’s law

Factors affecting variation of Conductivity

Temperature

Electrolytic solutions are formed by dissolving electrolytes into a solvent like water. The conducting capacity of an electrolytic solution hinges on the electrolyte dissolving and dissociating to produce ions in the solution.

Temperature plays a huge role in the solubility of an electrolyte. It is observed that with a rise in temperature, the solubility of an electrolyte in any given solvent also increases. This means that as the temperature increases, more and more electrolytes get dissolved which results in more dissociation and release of more ions. As more ions are released, the conduction capacity of the solution increases and therefore the conductivity of the solution increases.

Concentration of ions

Electricity passes through solids when there is movement of electrons. But electrolytic solutions do not conduct electricity via the movement of electrons. Rather the conduction of electricity through an electrolytic solution depends completely on the production of ions and their movement.

Electrolytes when dissolved in a solvent like water, dissociate to form positive and negative ions. The movement of these ions generates electricity. A greater number of ions make it easier to pass electricity through the solution. Conductivity of the solution measures the ease with which electricity is passed through the solution and with higher concentration of ions, the conductivity of the solution also increases.

Nature of the Electrolytes

Two broad classifications are made in regards to the strength of an electrolyte. Electrolytes can be classified into either strong or weak electrolytes. The strength of an electrolyte refers to the degree to which an electrolyte will undergo dissociation when an electric current is passed through it to facilitate its conduction

Depending on the nature of the electrolyte that is dissolved, the conductivity of the solution changes. If a strong electrolyte is dissolved, it readily dissociates and this creates a large concentration of ions in the solution which causes the conductivity of the solution to increase.

On the other hand, if a weak electrolyte is dissolved in the solution, it has a tendency to not dissociate readily. Only a fraction of the total dissolved electrolyte gets dissociated. This means a low amount of ions are present in the solution which results in less conductivity of the solution.

Factors affecting variation of Molar Conductivity

Conductivity is often measured as the conductivity per mole of an electrolyte and this is called the molar conductivity of the solution. The factors that affect the variation of molar conductivity include

Specific Conductance

Molar conductivity has a direct relationship with specific conductance and therefore for electrolytes that have higher specific conductance, the molar conductivity is also high.

Concentration

Strong electrolytes

For strong electrolytes, molar conductivity first increases and then decreases if the concentration decreases after a certain point. That is, for most strong electrolytes, molar conductivity and concentration have a direct relationship. With an increase in dilution, the concentration of ions decreases since no more new ions are produced.

This is due to the fact that strong electrolytes have a high tendency to almost completely dissociate into their constituent ions once they are dissolved in a solvent. When dilution happens, no more new ions are produced as the amount of solvent per ion increases. This means that the conducting capacity of the electrolytic solution decreases since the concentration of ions decreases. This decrease is translated as a decrease in molar conductivity.

Weak Electrolytes

When considering weak electrolytes, molar conductivity and molar concentration share an inverse relationship. With an increase in dilution of the weak electrolytic solution, the molar conductivity of the solution is observed to increase.

This happens because weak electrolytes do not completely dissociate when dissolved in a solvent. Only a fraction of the weak electrolytes get dissociated when it is first dissolved in a solvent. But when more solvent is added, further dissociation takes place.

Due to this extra dissociation, the number of ions that are present in the solution increases. A greater number of ions causes the conduction capacity of the solution to increase which is translated as an increase in the molar conductivity of the solution.

Conclusion

The temperature of the solution, number of ions and nature of the electrolytes are the factors that affect the variation of conductivity. As the temperature increases, more and more electrolytes get dissolved which results in more dissociation and release of more ions.

As more ions are released, the conduction capacity of the solution increases and therefore the conductivity of the solution increases. Conductivity of the solution measures the ease with which electricity is passed through the solution and with higher concentration of ions, the conductivity of the solution also increases.