Q28 of 55 Page 1

I) A) State Raoult’s law for a solution containing volatile components. Name the solution which follow Raoult’s at all concentrations and temperatures.

B) Calculate the boiling point elevation for a solution prepared by adding 10 g of to 200 g of water. ()


OR


Define the following terms:


i) Azeotropes


ii) Osmotic pressure


iii) Colligative properties


b) Calculate the molarity of 9.8% (w/w) solution of if the density of the solution is 1.02 g/ml. (Molar mass of is 98 g/mol)


A) Raoult's law states that for a solution of volatile liquids, the partial vapour pressure of each component in the solution is directly proportional to its mole fraction. Thus, if there is a solution of two liquid components 1 and 2, then

for component 1,


p1∝ x1


And,



For component 2,



Where,


p1 and p2 = Partial vapour pressure of two volatile components 1 and 2 of the solution


and = Vapour pressure of pure components 1 and 2


= Mole fractions of the components 1 and 2


The solution which follow Raoult’s at all concentrations and temperatures is called as an ideal solution.


B) elevation in the boiling point is determined by the formula:



Where,


– elevation in boiling point


- molal elevation constant


– molality of the solution


As we know,



Where,


- mass of solute in g


- mass of water/solvent in g


– molar mass of the solute in g


Using the equations, we get,




m = 0.450 m


now, putting the of m in the first eq.



0.450



Thus, the rise in the boiling point is 0.23 K


OR


a) i) Azeotropes can be defined as the mixture of two liquids with constant boiling point. Those solutions will have constant composition throughout distillations.
The boiling point of azeotrope can be either higher or lower to the boiling point of the components of the mixture.
For instance, Ethanol with water
Acetonitrile, water and methanol


ii) Osmotic pressure – It is the pressure required to prevent the solvent from passing through a semipermeable membrane from a region of higher concentration to a lower concentration region.


iii) Colligative properties are those properties of a solutions which depend upon the ratio of the number of solute particles to the number of solvent molecules in a solution. The properties include relative lowering of vapor pressure, elevation of boiling point, Osmotic pressure and depression of freezing point.


b) Given,


Composition = 9.8% (w/v) solution of


density = 1.02 g/ml.


Molar mass = 98 g/mol)


Molarity =






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