Problem 110 - Advanced Problems in Physical Chemistry for Competitive Examinations

Question

The molar conductance of a strong electrolyte at infinite dilution (a) tends to a finite value, which is above that at higher concentration (b) tends to a finite value, which is below that at higher concentration (c) tends to zero (d) tends to a finite value, which is equal

Step-by-Step Solution

Answer

The molar conductance of a strong electrolyte at infinite dilution tends to a finite value, which is above that at higher concentration.

Step 1: Understanding Molar Conductance at Infinite Dilution

The molar conductance of an electrolyte is defined as the conductance of all ions present in a solution containing one mole of electrolyte, and it increases with dilution. At infinite dilution, where the electrolyte is completely dissociated into its constitutive ions, the molar conductance reaches a maximum because the ions are far apart and there is minimal ion-ion interaction.

Step 2: Comparing Molar Conductance Values

As the concentration of the electrolyte decreases, i.e., as we move towards infinite dilution, the molar conductance increases because ions experience less electrostatic interaction and can move more freely. The value at infinite dilution is a finite number and represents the maximum molar conductance of the electrolyte.

Step 3: Selecting the Correct Answer

Based on the concept of molar conductance at infinite dilution, we can determine that the molar conductance of a strong electrolyte at infinite dilution tends to a finite value, which is above that at higher concentration. Therefore, the correct answer is (a).

Key Concepts

Electrolyte Dissociation

Electrolyte dissociation is a fundamental concept in understanding the behavior of electrolytes in solution. Electrolytes are substances that, when dissolved in water, disintegrate into positively and negatively charged ions. This dissociation process is crucial for the conductance of electricity in the solution, as the free ions are the carriers of electric charge.

The degree of dissociation is a measure of the extent to what an electrolyte splits into ions. Strong electrolytes, such as sodium chloride (NaCl), dissociate completely into their constituent ions (Na^+ and Cl^-) when dissolved in water. This is why strong electrolytes tend to have higher conductance, as they produce a greater number of ions to carry electrical current. In contrast, weak electrolytes only partially dissociate, resulting in fewer charge carriers and lower conductance.

At infinite dilution, the concept of electrolyte dissociation reaches its theoretical peak, since every ion is surrounded by enough solvent molecules to prevent recombination, and thus, conductance is maximized.

Ion-Ion Interaction

Ion-ion interaction refers to the forces between positively and negatively charged ions in a solution. These interactions can have a significant influence on the properties of the solution, including its conductance. In a concentrated solution, ions are closer together and tend to interact more intensely. These interactions can slow down the movement of ions because they are attracted or repelled by neighboring ions, somewhat akin to traffic congestion.

As a solution is diluted, the distance between ions increases, leading to a reduction in these interactions. At infinite dilution, it is assumed that these interactions are minimized to the extent that each ion behaves independently, without significant interference from other ions. This theoretical state is important for calculating intrinsic properties of ions, such as their individual contributions to the molar conductance, known as the limiting molar ionic conductivities.

Conductance in Chemistry

Conductance in chemistry is the measure of a solution's ability to conduct electricity. It depends on the presence of ions in the solution and their mobility. The higher the concentration of ions and the faster they can move, the greater the conductance.

The conductance of an electrolyte solution is often quantified through two specific terms: molar conductance and specific conductance. Molar conductance is defined as the conductance of a solution containing one mole of electrolyte per unit volume and is dependent on the concentration of the electrolyte. Specific conductance, on the other hand, is simply the conductance of a solution per unit length of the conductor and cross-sectional area.

At infinite dilution, where each ion contributes to conductance without being affected by the presence of other ions, molar conductance reaches its maximum value, termed as the limiting molar conductance. This value is key to understanding the intrinsic conductive properties of electrolytes, aiding in the study of electrochemical reactions, battery design, and various applications in electrochemistry.