Chemistry · Solutions. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Colligative properties of a dilute solution depend only on the number of solute particles in a given amount of solvent, not on what the particles are. They are lowering of vapour pressure, elevation of boiling point, depression of freezing point and osmotic pressure.
A non-volatile solute lowers the vapour pressure of the solvent. The solution must then be heated more before it boils and cooled more before it freezes. These changes are proportional to the molality, so they can be used to find the molar mass of a solute.
Hydration is water molecules surrounding ions. Hydrolysis is the reaction of the ions of a salt with water, which makes the solution acidic or basic.
Students use the mass of the solvent in grams in the molality, or give ΔT as the answer. Change grams of solvent to kg, then add ΔTb to the boiling point or subtract ΔTf from the freezing point.
Answer: 120 g mol−1
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