Question 1

What is molality?

Accepted Answer

Molality (m) is a measure of concentration defined as moles of solute per kilogram of solvent. It is different from molarity, which uses liters of solution. The symbol for molality is lowercase m, while molarity uses uppercase M.

Question 2

Why use molality instead of molarity?

Accepted Answer

Molality is temperature-independent because mass does not change with temperature, while volume does. This makes molality preferred for calculating colligative properties (boiling point elevation, freezing point depression, osmotic pressure).

Question 3

Is the solvent mass the same as the solution mass?

Accepted Answer

No. Solvent mass is only the mass of the solvent (e.g., water), not including the solute. Solution mass = solvent mass + solute mass. This is a common source of errors.

Question 4

How do I convert between molarity and molality?

Accepted Answer

For dilute aqueous solutions, molarity and molality are approximately equal. For concentrated solutions: m = M / (density - M × molar mass / 1000), where density is the solution density in kg/L.

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