Q. 145.0( 5 Votes )
Which of the following statements is false?
A. Two different solutions of sucrose of same molality prepared in different solvents will have the same depression in freezing point.
B. The osmotic pressure of a solution is given by the equation II = CRT
(where C is the molarity of the solution).
C. Decreasing order of osmotic pressure for 0.01 M aqueous solutions of barium chloride, potassium chloride, acetic acid and sucrose is
BaCl2 > KCl > CH3COOH > sucrose.
D. According to Raoult’s law, the vapour pressure exerted by a volatile component of a solution is directly proportional to its mole fraction in the solution.
Depression in freezing point = i × m × Kf
Now, i = van’t Hoff factor, m is the molality and Kf is the freezing constant of the solvent.
Now Kf is the property of the solvent and is different for different solvent.
Two different solutions of sucrose of the same molality prepared in different solvents will have different depression in freezing point.
Thus, statement (i) is false.
At a given temperature osmotic pressure is given by a formula i.e.
Where is the osmotic pressure, is the van’t Hoff factor, M is the molar concentration, R is the universal gas constant and T is the temperature.
Thus, statement (ii) is correct.
When the concentration of the solute is same osmotic pressure depends on the van’t Hoff factor.
Van’t Hoff factor for BaCl2 is 3, for KCl is 2, for CH3COOH is 2 and sucrose it is 1.
Since KCl is ionic it will completely dissolve in the solution its osmotic pressure is greater than that of CH3COOH.
Thus statement (iii) is also correct.
According to Raoult’s law, the partial vapor pressure of each component in the solution is directly proportional to its mole fraction.
Thus, for a component C in a solution
Where PC is the partial pressure of component C and xc is a mole fraction of C in a solution.
Thus statement (iv) is also correct.
Rate this question :
A statement of assertion followed by a statement of reason is given. Choose the correct answer out of the option given below each equation.
Assertion : When NaCl is added to water a depression in freezing point is observed.
Reason : The lowering of vapour pressure of a solution causes depression in the freezing point.
Chemistry - Exemplar
Match the laws given in Column I with expressions given in Column II.