`=>` Another class of solutions consists of solids dissolved in liquid. For example, sodium chloride, glucose, urea and cane sugar in water and iodine and sulphur dissolved in carbon disulphide.
`=>` Some physical properties of these solutions are quite different from those of pure solvents. For example, vapour pressure.
`=>` We know that under equilibrium conditions the pressure exerted by the vapours of the liquid over the liquid phase is called vapour pressure .
`=>` 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, the vapour pressure of the solution is decreased as the vapour pressure is solely from the solvent alone.
`=>` In the solution, at surface both solute and solvent molecules are there; thereby the fraction of the surface covered by the solvent molecules gets reduced and the number of solvent molecules escaping from the surface get reduced. Hence, 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.
`=>` For example, decrease in the vapour pressure of water by adding `1.0` mol of sucrose to one kg of water is nearly similar to that produced by adding `1.0` mol of urea to the same quantity of water at the same temperature.
`=>` Raoult’s law in its general form is stated as, for any solution the partial vapour pressure of each volatile component in the
solution is directly proportional to its mole fraction.
`color{green}("Explanation") :` In a binary solution, let us denote the solvent by `1` and solute by `2`. When the solute is non-volatile, only the solvent molecules are present in vapour phase and contribute to vapour pressure. Let `p_1` be the vapour pressure of the solvent, `x_1` be its mole fraction, `p_1^0` be its vapour pressure in the pure state. Then according to Raoult’s law
`color{red}(p_1 ∝ x_1)`
and `color{red}(p_1 = x_1 p_1^0)` .....................(8)
The proportionality constant is equal to the vapour pressure of pure solvent, `p_1^0`.
A plot between the vapour pressure and the mole fraction of the solvent is linear.
`=>` Another class of solutions consists of solids dissolved in liquid. For example, sodium chloride, glucose, urea and cane sugar in water and iodine and sulphur dissolved in carbon disulphide.
`=>` Some physical properties of these solutions are quite different from those of pure solvents. For example, vapour pressure.
`=>` We know that under equilibrium conditions the pressure exerted by the vapours of the liquid over the liquid phase is called vapour pressure .
`=>` 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, the vapour pressure of the solution is decreased as the vapour pressure is solely from the solvent alone.
`=>` In the solution, at surface both solute and solvent molecules are there; thereby the fraction of the surface covered by the solvent molecules gets reduced and the number of solvent molecules escaping from the surface get reduced. Hence, 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.
`=>` For example, decrease in the vapour pressure of water by adding `1.0` mol of sucrose to one kg of water is nearly similar to that produced by adding `1.0` mol of urea to the same quantity of water at the same temperature.
`=>` Raoult’s law in its general form is stated as, for any solution the partial vapour pressure of each volatile component in the
solution is directly proportional to its mole fraction.
`color{green}("Explanation") :` In a binary solution, let us denote the solvent by `1` and solute by `2`. When the solute is non-volatile, only the solvent molecules are present in vapour phase and contribute to vapour pressure. Let `p_1` be the vapour pressure of the solvent, `x_1` be its mole fraction, `p_1^0` be its vapour pressure in the pure state. Then according to Raoult’s law
`color{red}(p_1 ∝ x_1)`
and `color{red}(p_1 = x_1 p_1^0)` .....................(8)
The proportionality constant is equal to the vapour pressure of pure solvent, `p_1^0`.
A plot between the vapour pressure and the mole fraction of the solvent is linear.