Advertisements
Advertisements
प्रश्न
Derive the relationship between relative lowering of vapour pressure and molar mass of nonvolatile solute.
उत्तर
Let W2 g of solute of molar mass M2 be dissolved in W1 g of solvent of molar mass M1 . Hence number of
mole of solvent n1 and number of mole of solute n2 in solution.
`n_1=W_1/M_1 ` and `n_2=W_2/M_2` `(because "Number of moles (n)"="mass of the substance"/"molar mass of the substance")`
The mole fraction of solute x2 is given by
`x_2=n_2/(n_1+n_2)`
`x_2=(W_2/M_2)/(W_1/M_1+W_2/M_2)` .....(1)
For a solution of two components A1 and A2 with mole fraction x1 and x2 respectively, if the vapour pressure of pure component A1 is
`P_1^0 ` and that of component A2 is p_2^0 The relative lowering of vapour pressure is given by,
`(Deltap)/p_0^1=(p_1^0-p)/p_1^0`
`(Deltap)/p_0^1=(p_1^0x_2)/p_1^0`
`(Deltap)/p_0^1=x_2` .....(2)
Combining equations (1) and (2)
`(Deltap)/p_0^1=(p_1^0-p)/p_1^0=x_2=(W_2/M_2)/(W_1/M_1+W_2/M_2)`
For dilute solutions n1 >> n2. Hence n2 may be neglected in comparison with n1 in equation (1) and thus equation (3) becomes
`(Deltap)/p_0^1=n_2/n_1=(W_2/M_2)/(W_1/M_1)=(W_2M_1)/(W_1M_2)`
Knowing the masses of non-volatile solute and the solvent in dilute solutions and by determining experimentally vapour pressure of pure solvent and the solution, it is possible to determine molar mass of a non-volatile solute.
APPEARS IN
संबंधित प्रश्न
Vapour pressure of water at 293 K is 17.535 mm Hg. Calculate the vapour pressure of water at 293 K when 25 g of glucose is dissolved in 450 g of water.
The temperature at which vapour pressure of a liquid becomes equal to the atmospheric
pressure is _______.
(A) melting point
(B) boiling point
(C) 273 K
(D) 373 K
Which one of the statements given below concerning properties of solutions, describes a colligative effect?
12 g of urea is dissolved in 1 litre of water and 68.4 g of sucrose is dissolved in 1 litre of water. The lowering of vapour pressure of first case is ____________.
Relative lowering of vapour pressure is a colligative property because:
(i) It depends on the concentration of a non electrolyte solute in solution and does not depend on the nature of the solute molecules.
(ii) It depends on number of particles of electrolyte solute in solution and does not depend on the nature of the solute particles.
(iii) It depends on the concentration of a non electrolyte solute in solution as well as on the nature of the solute molecules.
(iv) It depends on the concentration of an electrolyte or nonelectrolyte solute in solution as well as on the nature of solute molecules.
Vapour pressure of a solution of a non-volatile solute is always ______
At 20°C, the vapour pressure of benzene is 70 torr and that of methyl benzene is 20 torr. The mole fraction of benzene in the vapour phase at 20°C above an equimolar mixture of benzene and methylbenzene is ______ × 10-2. (Nearest integer)
A non-volatile solute 'X' (molar mass = 50 g mol−1), when dissolved in 78 g of benzene, reduced its vapour pressure to 90%. Calculate the Mass of X dissolved in the solution.
The vapour pressure of pure water at a certain temperature is 23.80 mm Hg. If 1 mole of a non-volatile non-electrolytic solute is dissolved in 100g water, Calculate the resultant vapour pressure of the solution.
