# Why lowering of vapour pressure is not a colligative property?

In my textbook, it is written that lowering of vapour pressure is not a colligative property but relative lowering of vapour pressure is a colligative property. But why is that? There is literally no explanation given in my textbook as to why this is true. Please someone explain. I am so confused. Please help. (By lowering of vapour pressure I mean $$P_{0} - P_{S}$$ where $$P_{0}$$ is the vapour pressure of pure solvent and $$P_{S}$$ is the vapour pressure of the solvent containing non-volative solute. Relative Lowering in Vapour Pressure means $$\frac{P_{0} - P_{S}}{P_{0}}$$).

• Could you clarify with respect to the difference between 'relative lowering' and 'lowering'? May 6 at 18:27
• Consider reporting the whole sentences May 7 at 9:10
• Yeah, like @Alchimista said, please give us the complete quote; plus please include a full citation to the textbook (author, name, publication year, publisher, edition, etc.). Jun 23 at 4:23

A colligative property is a property which depends on number of solute particles and not on nature of solute particles. Relative lowering in vapour pressure is equal to the mole fraction of the solute . This can be derived using $$P_s=P_0\cdot x_\text{solvent}$$ where $$x$$ is the mole fraction and Po is the vapour pressure of pure solvent. Lowering of vapour pressure is also a colligative property as it is equal to $$\frac{x_\text{solute}}{P_0}$$. $$P_0$$ is a property of the solvent, not the solute.