• Freezing point of a substance is the temperature at which it’s liquid and solid phases have same vapour pressure. Depression in freezing point may be defined as the decrease of freezing point of a solvent on the addition of a non-volatile solute.
• E.g. Ethylene glycol is used as an antifreeze in car radiators which depresses the freezing point of water below 273K.
• Relation between depression of freezing point and molar mass of solute,
If w2 gram of a solute having molar mass M2 is present in w1 gram of the solvent and produces a depression in freezing point Tf of the solvent, then the molality of the solute is given by,
m = w2/M2 1000/w1
Thus, the relation can be given by
Tf = Kfm.
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