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

Equivalent conductance increases on dilution.

Step 1: Understanding Equivalent Conductance

Equivalent conductance (93) of an electrolyte is a measure of how well ions conduct electricity in solution when one equivalent of the electrolyte is dissolved. It is calculated using the formula 93 = 9b imes c, where 9b is the molar conductance and c is the concentration in equivalents per liter.

Step 2: Predicting Dilution Effect

With dilution, the concentration (c) of the strong electrolyte decreases as more solvent is added. This reduces the overall concentration of ions in the solution, thus increasing the distance between ions.

Step 3: Analyzing Conductance Change

When dilution occurs, the increase in distance between ions reduces the inter-ionic interactions, allowing ions to move more freely. This increased movement leads to an increase in molar conductance (9b), thereby increasing the equivalent conductance (93) as well.

Step 4: Final Conclusion

Based on the behavior of ions upon dilution, the equivalent conductance of a strong electrolyte increases. Therefore, the correct answer is option (c): increase on dilution.

Key Concepts

Strong Electrolyte

A strong electrolyte is a type of substance that completely dissociates into ions when dissolved in water. This complete ionization makes strong electrolytes excellent conductors of electricity. Some common examples include materials like sodium chloride (NaCl) and hydrochloric acid (HCl).
When these compounds dissolve, they produce a large number of free ions, which facilitate the conduction of electric current through the solution.
The key factor that distinguishes strong electrolytes from weak ones lies in the extent of ionization. Whereas strong electrolytes completely dissociate, weak electrolytes only partially dissociate, resulting in fewer free ions.

• Complete dissociation into ions
• Excellent electrical conductors
• Examples: NaCl, HCl

The properties of a strong electrolyte make them ideal for studying the effects of dilution on conductance. Their complete dissociation ensures a clear and measurable increase in conductance upon dilution.

Dilution Effect in Chemistry

In chemistry, dilution refers to the process of reducing the concentration of a solute in a solution, usually by adding more solvent. This concept is central to understanding how dilution affects the properties of solutions, especially electrical conductance.
For strong electrolytes, dilution decreases the concentration of ions per unit volume, thus increasing the distance between ions within the solution.
This reduction in ionic concentration affects how ions interact with each other. With more space to move around, the ions experience fewer collisions and less inter-ionic force, allowing them to move more freely.

• Addition of solvent reduces concentration
• Increased distance between ions
• Reduced inter-ionic interactions

Consequently, the mobility of ions in a diluted solution is enhanced, leading to increased conductance. This is because ions that can move more freely are better able to carry electrical charges across the solution, thus increasing the equivalent conductance.

Molar Conductance

Molar conductance (\(\Lambda_m\)) is an important concept in understanding how solutions conduct electricity. It refers to the conductance of all ions produced by one mole of an electrolyte in a solution. When a solution becomes more diluted, the molar conductance generally increases.
This increase is because the ions in solution experience less crowding and have more space to move freely and efficiently carry an electric current throughout the solution.
The increased freedom of movement for ions results in a higher capacity for the solution to conduct electricity.

• Reflects ions' contribution to conductance per mole
• Increases with dilution
• Enhanced ion mobility in dilute solutions

The relationship between concentration and molar conductance is inversely proportional. As dilution decreases the concentration, molar conductance increases. In the case of strong electrolytes, this increase is generally more pronounced, further resulting in an increase in equivalent conductance.