Free Solutions and Colloids MCQs with Answers

31. The lowest vapour pressure for 0.1 M solution exists for:

• A. Glucose
• B. NaCl
• C. BaCl2
• D. Al2(SO4)3

Explanation: The lowest vapour pressure would be observed in the case Al2SO4)3as it gives maximum no. of solute particles when dissolved due to dissociation.

32. A solution of glucose (C6H12O6) is isotonic with 4 g of urea (NH2 - CO - NH2 ) per liter of solution. The concentration of glucose is :

• A. 4 g/l
• B. 8 g/l
• C. 12 g/l
• D. 14 g/l

Explanation: Isotonic solutions are those solutions, which have the same osmotic pressure, this means that they have the same concentrations.

33. If liquids A and B form an ideal solution.

• A. the entropy of mixing is zero
• B. the free energy of mixing is zero
• C. the free energy as well as the entropy of mixing are each zero.
• D. the enthalpy of mixing is zero

Explanation: When A and b form an ideal solution, ∆Hmax = 0.

34. For which of the following parameters the structural isomers C2H5OH and CH3OCH3 would be expected to have the same values? (Assume ideal behavour)

• A. Boiling points
• B. Vapour pressure at the same temperature
• C. Heat of vaporization
• D. Gaseous densities at the same temperature and pressure

Explanation: Gas density is defined as the mass of the gas occupying a certain volume at specified pressure and temperature. Gaseous densities of ethanol and dimethyl ether would be same at same temperature and pressure because they have the same masses. The heat of vaporization, V.P. and b.pts will differe due to H - bonding in ethanol.

35. Equimolar solutions in the same solvent have:

• A. Different boiling and different freezing points
• B. Same boiling and same freezing points
• C. Same freezing point but different boiling points
• D. Same boiling point but different freezing points

Explanation: The elevation in the boiling point and the depression in the freezing point are colligative properties and depend on the number of solute particles.Equimolar solutions of non-electrolytes have the same number of solute particles.Hence, equimolar solutions of two non-electrolytes in the same solvent have the same boiling point and same freezing point.

36. Binary liquid mixtures which exhibit positive deviations from Raoult's law boil at ..... Temperature than the expected b.pt :

• A. Lower
• B. Higher
• C. Same
• D. Can't be said

Explanation: In mixtures showing a positive deviation from Raoult's Law, the vapour pressure of the mixture is always higher than from an ideal mixture.

37. Vapour pressure of a solvent containing non-volatile solute:

• A. More than the vapour pressure of a solvent
• B. Less than the vapour pressure of solvent
• C. Equal to the vapour pressure of solvent
• D. None of these

Explanation: Addition of non-volatile solute always lowers the vapour pressure.

38. Assuming each salt to be 90% dissociated, then which of the following will have highest osmotic pressure?

• A. Decimolar Al2(SO4)3
• B. Decimolar BaCl2
• C. Decimolar Na2SO4
• D. A solution obtained by mixing equal volumes and filtering

Explanation: Decimolar Al2(SO4)3 furnishes maximum number of ions.

39. The osmotic pressure of a solution can be accurately measured in the shortest possible time by:

• A. Berkeley and Hartley method
• B. Morse and Frazer method
• C. Pfeffer method
• D. None of the above

Explanation: It is more precise and takes minimum time.

40. At high altitudes the boiling point of water decreases because:

• A. Atmospheric pressure is low
• B. Temperature is low
• C. Atmospheric pressure is high
• D. None of the above

Explanation: The boiling occurs at lower temperature if atmospheric pressure is lower than 76 cm Hg.