Question

The increase in equivalent conductance of a weak electrolyte with dilution is due to : (a) Increase in degree of dissociation and decrease in ionic mobility (b) Decrease in degree of dissociation and decrease in ionic mobility (c) Increase in degree of dissociation and increase in ionic mobility (d) Decrease in degree of di?sociation and increase in ionic mobility

Short answer

(c) Increase in degree of dissociation and increase in ionic mobility.

Step-by-step solution

Understanding Equivalent Conductance

Equivalent conductance of an electrolyte is a measure of its ability to conduct electricity in solution. It is dependent on two factors - the degree of dissociation of the electrolyte into ions and the mobility of these ions.

Impact of Dilution on Degree of Dissociation

Diluting a weak electrolyte typically results in increased dissociation. This is because dilution decreases ion-ion interactions, making it easier for the electrolyte to dissociate into its constituent ions.

Impact of Dilution on Ionic Mobility

As the electrolyte solution is diluted, ion-ion and ion-solvent interactions change. Typically, reduced interactions result in increased ionic mobility because ions can move more freely through the solution.

Analyzing the Options

Based on the understanding of the effects of dilution on weak electrolytes, we can determine that the correct answer must involve an increase in both degree of dissociation and ionic mobility as a result of dilution.

Choosing the Correct Answer

Since dilution increases both the degree of dissociation and ionic mobility for weak electrolytes, the correct option is (c) Increase in degree of dissociation and increase in ionic mobility.

Key concepts

Degree of Dissociation

The degree of dissociation is a measure of the extent to which a substance breaks down into its constituent ions when dissolved in a solvent. It is a crucial factor in determining the conductivity of an electrolyte solution. Through dilution, the concentration of the electrolyte decreases, and it becomes less likely for ions to recombine into the undissociated molecule. This increased separation of ions enhances the degree of dissociation and therefore increases the solution's ability to conduct electricity. For weak electrolytes, such as acetic acid, the degree of dissociation is not complete and significantly depends on the concentration of the electrolyte. In dilute solutions, weak electrolytes exhibit a higher degree of dissociation, which explains their increased conductivity upon dilution.

Ionic Mobility

Ionic mobility refers to the velocity at which an ion moves through a solvent in response to an electric field. It is a key parameter in assessing an electrolyte's conductance. When an electrolyte solution is diluted, the ions are further apart, reducing the frequency of ion-ion collisions. This reduction in collisions allows ions to move more freely, increasing their mobility.Moreover, the solvation shell, which is the layer of solvent molecules surrounding an ion, is less crowded in a dilute solution. This can lead to a decrease in the viscosity of the solution and further facilitate ion movement, augmenting ionic mobility. Higher ionic mobility results in better conductivity of the solution because ions can travel faster to the electrodes when an electric potential is applied.

Electrolyte Dilution

Electrolyte dilution involves adding a solvent, typically water, to decrease the concentration of the electrolyte in the solution. Diluting an electrolyte impacts several properties of the solution, including ionic strength, degree of dissociation, ionic mobility, and conductivity.With dilution, the ionic strength of the solution decreases, which weakens the electrostatic interactions between ions. As a consequence, there's a decrease in the recombination rate of the ions, promoting a greater degree of dissociation. Moreover, the relative dielectric constant of water being high, further helps in stabilizing the ions apart, thus improving dissociation upon dilution.Overall, dilution of an electrolyte solution typically leads to improved conductance, especially for weak electrolytes, due to both increased degree of dissociation and ionic mobility.

Conductivity in Solutions

Conductivity is a fundamental property that indicates how well a solution can carry an electric current. It depends on the presence of free ions capable of transporting electric charge. In electrolyte solutions, conductivity is influenced by the concentration of ions, their mobility, and the degree of dissociation.The conductance of an electrolyte solution is quantified by its ability to allow electric current to pass, which in turn is dependent on the free movement of ions. Thus, factors that increase ionic mobility, such as electrolyte dilution, will enhance the solution's conductivity. Conversely, higher concentrations of electrolytes, where ions are closely packed, may lead to decreased conductivity due to increased ion-ion interactions that limit mobility.Ultimately, the relationship between electrolyte concentration and solution conductivity is non-linear, with weak electrolytes showing a marked increase in conductivity at higher dilutions due to a significantly increased degree of dissociation.