Introduction
Molality and molarity are two different ways to express the concentration of a solution. While both are related to the amount of solute in a given amount of solvent, there are situations where the molality of a solute may not be equal to its molarity.

Molality vs. Molarity
Molality is defined as the number of moles of solute per kilogram of solvent, while molarity is defined as the number of moles of solute per liter of solution. In other words, molality takes into account the mass of the solvent, while molarity does not.

When Molality ≠ Molarity
The molality of a solute will not be equal to its molarity when the density of the solution changes with temperature. This can occur because the mass of the solvent changes with temperature, while the volume remains constant. As a result, the concentration of the solution changes, even though the amount of solute remains the same.

Example
For example, consider a solution of sucrose (C12H22O11) in water. Suppose we have 1 mole of sucrose dissolved in 1 liter of water at 25°C. At this temperature, the density of the solution is 1.04 g/mL, which means that the mass of the solution is 1040 g.

If we increase the temperature of the solution to 50°C, the density of the solution decreases to 1.02 g/mL. This means that the mass of the solution is now 1020 g. However, the amount of solute (1 mole of sucrose) remains the same.

As a result, the molality of the solution has changed from 1 mole/kg to 0.98 mole/kg, while the molarity remains the same at 1 mole/L.

Conclusion
In conclusion, the molality of a solute may not be equal to its molarity when the density of the solution changes with temperature. This is because molality takes into account the mass of the solvent, while molarity does not. It is important to keep this in mind when working with solutions that are sensitive to changes in temperature.

Molality of a solution cannot be equal to the molarity of a solution. Until and unless volume of solution is equal to weight of solvent, molarity is never equal to molality.