MOLE FRACTION AND MOLALITY IS INDEPENDENT OF TEMPERATURE BUT NORMALITY AND MOLALITY CHANGES WITH TEMPERATURE, WHY?
Mole fraction and molality are independent of temperature because they are defined based on the number of moles of solute and solvent, respectively, which do not change with temperature. On the other hand, normality and molarity change with temperature because they are defined based on the volume of solution, which can vary with temperature.
Let's explain each of these terms in more detail:
1. Mole fraction (X): It is the ratio of the moles of a solute to the total moles of solute and solvent in a solution. Mathematically, it is expressed as:
X = moles of solute / (moles of solute + moles of solvent)
Since the number of moles of solute and solvent do not change with temperature, the mole fraction remains constant regardless of temperature changes.
2. Molality (m): It is defined as the number of moles of solute per kilogram of solvent. Mathematically, it is expressed as:
m = moles of solute / mass of solvent (in kg)
Molality is also independent of temperature because it is based on the mass of the solvent, which does not tend to change significantly with temperature.
3. Normality (N): It is a measure of the concentration of an acid or base solution, which is defined as the equivalent weight of solute per liter of solution. Mathematically, it is expressed as:
N = (equivalent weight of solute) / (volume of solution in liters)
The volume of the solution can change with temperature due to thermal expansion or contraction. Hence, normality is temperature-dependent as it involves the volume measurement.
4. Molarity (M): It is defined as the number of moles of solute per liter of solution. Mathematically, it is expressed as:
M = moles of solute / volume of solution (in liters)
Molarity is also temperature-dependent because it is based on the volume of the solution, which can change with temperature.
In summary, mole fraction and molality remain unaffected by temperature since they are based on the number of moles (independent of volume). On the other hand, normality and molarity can change with temperature since they are based on the volume of the solution, which can vary with temperature.