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Sunday, May 24, 2020

Which of the following pair of solution (aq.) contain isotonic solution at same temperature? (Assume 100 % ionisation of electrolytes) (1) 0.1 M NaCI and 0.2 M CaCI2(2) 0.1 M NaCI and 0.3 M AICI3 (3) 0.3 M NaCI and 0.1 M AICI3 (4) 0.3 M NaCI and 0.2 CaCI2

Freezing point of pure liquid A is T K. If some amount of non-electrolyte non-volatile impurity is added in A, an ideal solution is formed. On cooling at 200 K, only 30% (by mass) liquid A is present and at 201 K, 60 % (by mass) liquid A is present. The value of T is .

Liquid A and B form ideal solution at temperature T. Mole fraction of A in liquid and vapour phase are 0.4 and 4/13 respectively, when total pressure is 130 torr. The vapour pressure (in torr) of A and B in pure state at temperature T are respectively.

We know that partial pressure of components of a binary solution containing A and B component.
(1) In liquid state:
P_A= P°_A X_A and  P_B= P°_B X_B
(2) In Vapour phase: 
P_A= P_T Y_A  and P_B= P_T Y_B

Where X_A and X_B is mole fraction in liquid state while Y_A and Y_B is mole fraction in vapour phase

What is the relation between Raoult' law and Dalton's ?

According to Raoult's Law: The partial pressure of any volatile component of a solution at any temperature is equal to the vapour pressure of the pure component multiplied by the mole fraction of that component in the solution.
      Where XA­ and XB is the mole fraction of the component A and B in liquid phase respectively

According to Dalton's Law:
The vapour behaves like an ideal gas, then according to Dalton's law of partial pressures, the total pressure PTis given by:
 Partial pressure of the gas = Total pressure x Mole fraction
                                        PA = PT YA and PB =PT YB
Where YA­ and YB is the mole fraction of the component A and B in gas phase respectively
Combination of Raoult's and Dalton's Law:
(3) Thus, in case of ideal solution the vapour phase is phase is richer with more volatile component i.e., the one having relatively greater vapour pressure

Graph Between 1/YA Vs 1/XA:
According to Dalton's law of partial pressures, the total pressure PT is given by:
 Partial pressure of the gas = Total pressure x Mole fraction
Where YA­ and YB is the mole fraction of the component A and B in gas phase respectively
According to Raoult's law:
On rearrangement of this equation we get a straight line equation:
Illustrative Examples: