SOLUTIONS QUIZ-5

Q1. Observe the following abbrevations π_obs= observed colligative property π_cal= theoretical colligative property assuming normal behaviour of solute. Van’t Hoff factors (i) is given by

•  i=π_obs ×π_cal
•  i=π_obs+π_cal
•  i=π_obs-π_cal
•  i=π_obs/(π_cal )

Solution
Van’t Hoff factor (i) is given by i=(observed value of colligative property)/(normal value of colligative property ) The normal value of colligative property is the theoretically calculated value assuming no association or dissociation. ∴ i=π_obs/π_cal

Q2.Normality of 2 M H_2 〖SO〗_4 is

•  2 N
•  4 N
•  N/2
•  N/4

Solution
∵ Basicity of H_2 〖SO〗_4 = 2 Normality = molarity× basicity of acid =2×2=4 ∴ 2 M H_2SO_4 = 4 N H_2SO_4

Q3.  20 g of binary electrolyte (mol. wt. =100) are dissolved in 500 g of water. The depression in freezing point of the solution is 0.74℃ (k_f=1.86 Km^(-1)) the degree of ionisation of the electrolyte is

•   50%
•  75%
•  100%
•  0%

Solution
∆T=(1000×k_f×w)/(m×500) 0.74=(1000×1.86×20)/(m×500) m=100 Actual molecular mass =100 ∴ The degree of ionisation of the electrolyte is 0% .

Q4. Molarity of 0.2 N H_2 SO_4 is

•  0.2
•  0.4
•  0.6
•  0.1

Solution
Normality of acid = molarity × basicity Molarity = N/basicity = 0.2/2=0.1M

Q5.The condition under which Nernst distribution law will not hold true is :

•  None of the above
•  The solute does not cause any change in the mutual solubility of the two solvents
•  The molecular state of the solute is the same in both solvents
•  Temperature is constant

Solution
 In a,b,c the choices reflect for the validity of law

Q6. Which of the following associated with isotonic solutions is not correct?

•  They will have the same osmotic pressure
•  They have same weight concentrations
• Osmosis does not take place when the two solutions are separated by a semipermeable membrane
•  They will have the same vapour pressure

Solution
The solutions having the same osmatic pressure are called isotonic solution. They have same weight concentrations

Q7.The distribution law holds good for :

•  None of these
•  Both (C) and (D)
•  Heterogeneous systems
•  Homogeneous systems

Solution
The two solvents in which a solute is to be distributed shows K=c_1/c_2 only when two liquids are immiscible, i.e., No. of phase ≥ 2 or heterogeneous systems

Q8.The energy that favours dissolution of a solute in water is known as :

•  Exothermic energy
•  Hydration energy
•  Lattice energy
•  Ionization energy

Solution
More is the hydration energy of an ionic solute, more is its solubility.

Q9.Which is correct about Henry’s law?

•  There should not be any chemical interaction between the gas and liquid
•  All of the above
•  The pressure applied should be high
•  The gas in contact with the liquid should behave as an ideal gas

Solution
According to Henry’s law, the gas in contact with the liquid should behave as an ideal gas

Q10. During depression of freezing point in a solution the following are in equilibrium :

•  Liquid solvent, solid solute
•  Liquid solvent, solid solvent
•  Liquid solute, solid solute
• Liquid solute, solid solvent

Solution
During freezing of a solution only solvent freezes out and the equilibrium exists between solid and liquid forms of solvent.