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Molality is a measure of the concentration of a solute in a solution. It's expressed as moles of solute per kilogram of solvent. This is different from molarity, which is moles of solute per liter of solution. To understand molality, it's important to recognize why we use it, especially in boiling point elevation problems. It's useful because it depends only on the amount of solute and solvent, not the temperature or pressure, providing a very stable measure of concentration.
To calculate molality, you need:

• Moles of solute: This is given by the amount of solute, often found using its chemical formula and molar mass.
• Mass of solvent in kilograms: This might require converting from grams, making sure to subtract any solute mass from the total solution mass.

For example, if you dissolve NaHSO鈧� in water, you find the number of moles of NaHSO鈧� and the mass of water in kilograms, then divide the two to find molality. In the provided exercise, the molality of NaHSO鈧� was found to be 0.101 mol/kg, showing how these calculations come about in real-world problems.

The Van't Hoff factor, commonly designated as "i", indicates the number of particles a solute generates when it dissolves. It's crucial in colligative properties, such as boiling point elevation and freezing point depression, because these depend on the number of particles in a solution, not the type of particles.
For electrolytes like NaHSO鈧�, which dissociate in solution, the Van't Hoff factor helps us understand how many ions are produced. NaHSO鈧� dissociates into two ions: Na鈦� and HSO鈧勨伝. Thus, the Van't Hoff factor for NaHSO鈧� is 2.
The Van't Hoff factor plays a significant role in the formula for boiling point elevation:

• 螖T鈧� = Kb 脳 molality 脳 i

Here, "i" directly affects the boiling point elevation. The more particles produced, the higher the boiling point elevation. Understanding this concept is essential for applying colligative properties in solutions where electrolyte dissociation occurs.

Molarity is another way to express the concentration of a solution, often denoted as M. It is the number of moles of solute per liter of solution. In contrast to molality, molarity depends on the entire volume of the solution, which can vary with temperature and pressure.
Calculating molarity involves knowing:

• The amount of solute in moles: Usually derived from the solute's weight and molar mass.
• The volume of the solution in liters: This includes both solute and solvent.

For the NaHSO鈧� solution in the example, the initial concentration was given as 0.10 M. Molarity was important here as a starting point before converting to molality for the boiling point elevation calculation. While molarity is easy to calculate and widely used, it can be less precise than molality in certain scientific calculations, especially where temperature changes are involved.