Question

In which mode of expression, the concentration of a solution remains independent of temperature?

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

Hint:

Molality is used in colligative properties calculations because it remains constant irrespective of temperature changes.

Answer 1

The Correct Option is D

Step 1: {Understanding concentration units} 
Molarity \( (M) \) and normality \( (N) \) depend on volume, which changes with temperature. However, molality \( (m) \) is defined as: \[ m = \frac{{Moles of solute}}{{Mass of solvent in kg}} \] Since mass is unaffected by temperature changes, molality remains constant. 
Step 2: {Why molality is temperature-independent} 
Molality does not involve volume, which expands or contracts with temperature. Hence, it is the preferred unit in temperature-dependent studies. 
 

Answer 2

Step 1: Understand different modes of expressing concentration
Common ways to express the concentration of a solution include:
- Molarity (mol/L)
- Molality (mol/kg)
- Normality (eq/L)
- Mole fraction (unitless ratio)
- Mass percent or volume percent

Step 2: How temperature affects concentration units
Some of these concentration expressions depend on volume (e.g., molarity, normality), and volume changes with temperature due to thermal expansion or contraction.
Others depend on mass (e.g., molality), and mass is unaffected by temperature.

Step 3: Define molality
Molality (m) = \( \frac{\text{moles of solute}}{\text{mass of solvent in kg}} \)
Since both moles and mass are independent of temperature, molality remains unchanged when the temperature changes.

Step 4: Final Answer
The mode of concentration that remains independent of temperature is:
Molality