Problem 43 - A Complete Resource Book in Chemistry for JEE Main

Question

What is the effect of dilution on the equivalent conductance of strong electrolyte? (a) decrease on dilution(b) remains unchanged (c) increase on dilution (d) none of these

Step-by-Step Solution

Answer

(c) Increase on dilution.

Step 1: Understanding Equivalent Conductance

Equivalent conductance (\(\lambda_{eq}\)) is defined as the conductivity of an electrolyte solution divided by the molarity of the solution. It relates how well ions in a solution can carry electrical current when the solution is optimally diluted.

Step 2: Effect of Dilution on Ion Mobility

Diluting a solution results in a greater degree of ion dissociation for strong electrolytes, as they are fully ionized in solution. This increases the mobility of ions as the ions are less crowded and are more free to move.

Step 3: Relation Between Dilution and Conductance

As dilution increases, the distance separating ions increases, reducing the interactive forces such as electrostatic attractions or repulsions between ions. Consequently, the ions are able to move more freely through the solution, which increases the equivalent conductance.

Step 4: Conclusion

From the above understanding, we can deduce that for strong electrolytes, equivalent conductance increases upon dilution due to enhanced ion mobility and decreased ion-ion interactions.

Key Concepts

Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions when dissolved in a solvent like water. Unlike weak electrolytes, which only partially ionize in solution, strong electrolytes break apart fully, allowing the ions to conduct electricity efficiently. This characteristic makes them crucial in discussions about electrical conductivity in solutions.
Examples of strong electrolytes include salts like sodium chloride (NaCl), strong acids like hydrochloric acid (HCl), and strong bases like potassium hydroxide (KOH). When these substances dissolve, they release all their constituent ions into the solution, significantly increasing the solution's conductivity.
Some key points about strong electrolytes:

• They fully dissociate into ions in solution.
• They have a higher conductivity compared to weak electrolytes.
• They are often used in batteries and electrochemical applications.

Understanding strong electrolytes is essential, especially when considering how changes like dilution impact their conductivity.

Ion Mobility

Ion mobility refers to the ease with which ions can move through a solution. When a solution is dilute, ions have more space to move around as they are no longer packed closely together. This increased freedom leads to higher ion mobility because ions face less resistance. In concentrated solutions, ions are close to each other, facing high interaction forces such as mutual attraction or repulsion, which can hinder their movement. However, in more dilute solutions, these interactions decrease, allowing ions to move swiftly. Factors affecting ion mobility include:

• Concentration of the solution: Lower concentrations reduce interactions.
• Viscosity of the solvent: Less viscous solvents facilitate easier ion movement.
• Temperature: Higher temperatures usually increase mobility.

Grasping the concept of ion mobility helps in understanding why the conductivity of a solution might increase when a strong electrolyte is diluted.

Dilution Effect

The dilution effect describes how the conductivity of a solution changes as it is diluted. For strong electrolytes, diluting the solution typically increases the equivalent conductance. This happens because the ions are more spread out and can move more freely. When a solution contains fewer ions per unit volume, they experience less interaction with each other, essentially letting them travel unimpeded. Dilution decreases the concentration but increases ion mobility, and this increase in mobility outweighs the lower ion density, leading to higher equivalent conductance.
Considerations for the dilution effect include:

• The extent of ion dissociation, which is total for strong electrolytes.
• The influence on ion interaction forces, which diminish with dilution.
• The overall impact on equivalent conductance, which generally goes up.

In essence, as the solution becomes more dilute, ions move with less restriction, enhancing the overall conductivity and demonstrating the dilution effect.