Lowering of vapour pressure pdf

Jump to Page. Search inside document. Vapor Pressure Lowering of Solution When a non-volatile solute one that does not exert vapor pressure is dissolved in liquid, the vapour pressure exerted by the liquid decreases. Allen A Espinosa. Mukesh Hacker. German Tortosa. Romulo Vincent Perez. Heather Wright. Dong Phan Cong. Subhasish Sau. Eredson Libutlibut.

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Floating Leaf Disks for Investigating Photosynthesis. Pilm Wizard. Swapnil Kumar. Direct immersion single drop micro-extraction method for multi-class. These properties can be observed clearly if the solution is very dilute, the solute is non-volatile and the solute does not dissociate or associate in the solution. There are four colligative properties of solutions.

The Concept of Vapour Pressure:. If a container is partially filled with a liquid, a portion of the liquid evaporates to fill the remaining volume of the container with vapour. The molecules of liquid evaporated are in continuous random motion, they collide with the walls of the container and with each other.

Thus they create pressure on the walls of the container and on the liquid. At the same time some molecules which have left liquid return back to the liquid, the process is called condensation. After some interval of time, an equilibrium is established between the two phases of substance.

At this stage, the rate of evaporation is equal to the rate of condensation. The pressure exerted by the vapours of the liquid on the surface of the liquid when equilibrium is established between liquid and its vapour is called vapour pressure of the liquid.

The temperature at which vapour pressure of the liquid is equal to the external pressure is called boiling temperature at that pressure. Relation Between Vapour Pressure and Temperature:. Clausius Clapeyron Equation:.

Using this relation we can find vapour pressure at some another temperature when its value at some temperature is known. Lowering of Vapour Pressure:.

Liquids at a given temperature vapourize and under equilibrium conditions, the pressure exerted by the vapours of the liquid over the liquid phase is called vapour pressure [Fig a ]. In a pure liquid, the entire surface is occupied by the molecules of the liquid. If a non-volatile solute is added to a solvent to give a solution [Fig. This vapour pressure of the solution at a given temperature is found to be lower than that of the pure solvent at the same temperature.

In the solution, the surface has both solute and solvent molecules; thereby the fraction of the surface covered by the solvent molecules gets reduced. Consequently, the number of solvent molecules escaping from the surface is correspondingly reduced thus, the vapour pressure is also reduced.

The decrease in the vapour pressure of solvent depends on the quantity of non-volatile solute present in the solution, irrespective of its nature. Reasons for Lowering of Vapour Pressure:. The evaporation of liquid and evaporation of the liquid is a surface phenomenon. It is directly proportional to the surface area available for evaporation.

Due to the addition of non-volatile solute the surface area of liquid decreases. If a solution only acquired from two components is solvent and solute. The correlation between both mole fractions can be expressed as:. This third expression is what we can use to calculate how big the vapor pressure lowering number of a solution is.

To find the vapor pressure lowering, we can see it from the first and third expression. Bear in mind that if we used the first expression, then the mole fraction that is used is Xp solvent mole fraction , but if we use the third expression, the mole fraction that is used is Xt solute mole fraction. The above explanation focused more on a solution with a non-volatile solute while what happened if a solution is made from a volatile solute? Where the ideal solution can be acquired if an interaction between solute — solute, solvent — solvent, or solute — solvent got an almost equal number.

When a dissolving of a solute inside a solvent is freed by heat exoterm , then the eltalphy is negative. A strong interaction between acetone — water or acetone chloroform is caused by a hydrogen bond between each substance.