Question

The concentration of a solution can be expressed in molarity, normality, formality, and molality. Among them, which mode of expression is the most accurate for all conditions?

• A. Molarity
• B. Formality
• C. Normality
• D. Molality

Hint:

For accurate measurements, especially in experiments with temperature variations, always prefer molality over volume-based concentration units like molarity.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Accuracy in concentration terms depends on their dependence on temperature. Molarity, normality, and formality are volume-dependent, and volume changes with temperature.

Step 2: Detailed Explanation:
• Molarity (M): Moles of solute per liter of solution. Volume of solution is temperature-dependent. • Normality (N): Gram equivalents of solute per liter of solution. Also volume-dependent. • Formality (F): Formula weight of solute per liter of solution. Volume-dependent. • Molality (m): Moles of solute per kilogram of solvent. Mass is independent of temperature, making molality the most accurate concentration term under varying temperature conditions.

Step 3: Final Answer:
Molality is the most accurate expression as it is independent of temperature, which corresponds to option (D).