Distribution law
Distribution law According to Nernst’s Distribution law (1891) or Partition law, “When a solute is taken up with two immiscible liquids, in both of which the solute is soluble, the solute distributes itself between the two liquids in such a way that the ratio of its concentration in the two liquid phases is constant at a given temperature provided the molecular state of the distributed solute is same in both the phases”. I.e. Where are the concentrations of the solute in two phases. is called distribution coefficient or...
read moreHennery’s law
According to Henry, “The ratio of concentration of a gas in the liquid phase to that in the gaseous phase is constant at constant temperature”. i.e. Or “The mass of the gas (m) that dissolves in a given volume of the liquid at a constant temperature is proportional to the partial pressure (p) of the gas in equilibrium with the liquid”. i.e. or m = kp where ‘k’ is called Henry constant.
read moreDepression of freezing point
We know that a liquid freezes only when its vapour pressure becomes equal to that of its solid form. But since the vapour pressure of a liquid is lowered by the addition of a solute, hence the freezing point of the solution is lowered which is known as depression of freezing point It also depends upon the number of moles of the added non-volatile solute. Thus, where = molal freezing point lowering constant cryoscopic constant and ‘m’ =molality of the solute. According to Van’t Hoff, where ‘T’= freezing...
read moreElevation of boiling point
Elevation of boiling point It is known that a liquid boils only when its vapour pressure becomes equal to the atmospheric pressure. But when a non-volatile solute is added to the solvent, the vapour pressure is lowered. In order to boil the solution, the temperature has to be raised further so as to make its vapour pressure equal to atmospheric pressure. The raising of temperature is known as elevation of boiling point . It depends upon the number of moles of the added non-volatile solute. Thus, Where = molal boiling point elevation...
read moreOsmotic pressure
It is the flow of solvent molecules from the solvent or less concentrated solution to solution or more concentrated solution through a. semi-permeable membrane. The osmotic pressure is developed by osmosis. It may be defined as, “The excess pressure which must be applied to the solution in order to just prevent the flow of the solvent into it through a semi permeable-membrane”. OR “The excess of pressure which must be applied to the solution in order to increase its vapour pressure until it becomes equal to that of the...
read moreRaoult’s law
Raoult’s law (1887) According to this law, “The relative lowering of vapour pressure is equal to the ratio of the moles of the solute and the total number of moles in the solution”, i.e., the mole fraction of the solute present in solution. Thus, where ‘n’ = Number of moles of solute and ‘N’ = Nmuber of moles of solvent. For very dilute solution, N >> n, the above equation may be written as: Let ‘w’ be the mass of solute, ‘W’ be the mass of solvent, ‘m’ the...
read moreVapour pressure
Vapour pressure of a liquid is the pressure exerted by the vapour in equilibrium with the liquid at a specific temperature. The vapour pressure of a solvent is constant at constant temperature. But when a non-volatile solute is dissolved in it, the vapour pressure is lowered and the lowering of vapour pressure is proportional to the amount of solute dissolved. Let ‘p’ be the vapour pressure of pure solvent and pS be that of solution, the lowering of vapour pressure will be The ratio of the lowering of vapour pressure to the...
read moreTypes of Solutions
The solutions may be classified on the basis of solubility. The extent to which a solute dissolves in a solvent to form a saturated solution is a measure of solubility. It depends upon: (a) Nature of solute and solvent (b) Temperature (c) Pressure (If gas is a solute) All solutions containing less amount of solute than the saturated solution at a given temperature are said to be unsaturated solutions. While a solution holding more amount of the solute than the saturated solution at the same temperature is called a...
read moreSolution
A homogeneous mixture of two or more substances having uniform properties such as density, refractive index etc., is known as solution. The substance which is present in smaller quantity in the solution is called solute and which is present in larger quantity is called solvent. E. g. In the aqueous solution of sugar, sugar is solute and water is solvent. The concentration of solutions is expressed by following different ways: 1. As percentage by weight: If w g of solute is present in W g of solution then 2. As gram per litre : It is...
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