Solution and Colligative Properties Exercise # 2

Exercise # 2 1. [Multiple Correct Choice Type Questions] For the given electrolyte AxBy, the degree of dissociation '' can be given as (A)  = 2. Part # I i –1 x + y –1 (B) i = ( 1– )+ x + y (C)  = 1– i 1– x – y (D) None P vs d (where P is osmotic pressure of solution of a solute of mol. wt. m and d is its d density at temperature T. Pick out the correct statements about the plots : P ST ST (A)  d  = (B) The intercept of the plot  d 0 m m A graph plotted between P (C) The intercept of the plot =  d   d0 P (D)  d  is independent of temperature d0 3. Which of the following is/are correct for an ideal binary solution of two volatile liquids (eg. benzene & toluene)? (A) Its vapour is always richer in the more volatile component (compared to the liquid). (B) The liquid will gradually become richer in the less volatile component if such a mixture is boiled (distilled). (C) The PT (ie. the total pressure) above the solution will be the sum of the vapor pressures of the two pure components. (D) The boiling point of the solution will be less than the boiling points of the two components. 4. The diagram given below represents boiling point composition diagram of solution of component A and B, which is/are incorrect among the following? (A) The solution shows negative deviation (B) A-B-interactions are stronger than A-A and B-B (C) The solution is ideal solution (D) The solution shows positive deviation. TºA TºB T(k) xB 5. According to Henry’s law , the partial pressure of gas (Pg) is directly proportional to mole fraction of gas in dissolved state , i.e., Pgas = KH . Xgas where KH is Henry’s constant. Which are correct ? (A) KH is characteristic constant for a given gas–solvent system (B) Higher is the value of KH , lower is solubility of gas for a given partial pressure of gas (C) KH has temperature dependence (D) KH increases with temperature 6. Which of the following concentration factors can be calculated if the mole fraction and density of an aqueous solution of HCl are known ? (A) Molality 7. (B) Molarity Consider following solutions : I : 1 M aqueous glucose solution II : 1M aqueous sodium chloride solution III : 1M aqueous ammonium phosphate solution IV : 1M benzoic acid in benzene Select correct statements for the above solutions : (A) All are isotonic solutions (B) III is hypertonic of I, II and IV (C) IV is hypotonic of I, II and III (D) II is hypotonic of III but hypertonic of I and IV (C) Percent by mass (D) Normality SOLUTION AND COLLIGATIVE PROPERTIES 8. Which combination of (I) vapour pressure, (II) intermolecular forces and (III) Hvap (latent heat of vaporisation) is matched correctly I II III (A) high weak small (B) high s trong large (C) low weak large (D) low strong s mall 9. Which is/are true about ideal solutions ? (A) The volume of mixing is zero (B) The enthalpy of mixing is zero (C) The entropy of mixing is zero (D) The enthalpy of mixing is negative 10. Freezing point lowering expression is Tf = Kfm (molality) Which of the following assumptions are considered for the validity of above equation ? (A) The solution is dilute (B) The Hf (latent heat of fusion of solvent) is independent of temperature between the actual and normal freezing point (C) The solid-phase consists of pure solvent when solution is allowed to cool (D) Tf is not equal to 3Kf for 3 mol L–1 solution 11. At 35°C, the vapour pressure of CS2 is 512 mmHg, and of acetone is 344 mmHg. A solution of CS2 and acetone in, which the mole fraction of CS2 is 0.25, has a total vapour pressure of 600mmHg. Which of the following statements is/are correct ? (A) A mixture of 100 mL of acetone and 100 mL of CS2 has a volume of 200 mL (B) When acetone and CS2 are mixed at 35°C, heat must be absorbed in order to produce a solution at 35°C (C) Process of mixing is exothermic (D) Entropy of mixing is zero 12. Which is/are correct statement(s) ? (A) When mixture is more volatile, there is positive deviation from Raoult’s law (B) When mixture is less volatile, there is negative deviation from Raoult’s law (C) Ethanol and water form ideal solution (D) CHCl3 and water form ideal solution 13. At 40°C, vapour pressure in Torr of methanol and ethanol solution is P = 119x + 135 where x is the mole fraction of methanol. Hence (A) vapour pressure of pure methanol is 119 Torr (B) vapour pressure of pure ethanol is 135 Torr (C) vapour pressure of equimolar mixture of each is 127 Torr (D) mixture is completely immiscible 14. Which one of the statements given below concerning properties of solutions, describes a colligative effect ? (A) Boiling point of pure water decreases by the addition of ethanol (B) Vapour pressure of pure water decreases by the addition of nitric acid (C) Vapour pressure of pure benzene decreases by the addition of naphthalene (D) Boiling point of pure benzene increases by the addition of toluene 15. For a dilute solution having molality m of a given solute in a solvent of mol.wt. M , b.pt. T b and heat of vaporisation   Tb  per mole H ;  is equal to :    m  m 0 (A) Molal elevation constant of solvent RTb2 M (B) ΔH ; where M in kg Hvap and R in J mol–1 vap RTb2 M (C) ΔS ; where M in kg ; Svap and R in J mol–1 vap RTb2M (D) 1000ΔH ; where M in g ; R and Hvap expressed in same unit of heat. vap 16. Which facts are true when we use van’t Hoff equation PV = CST for osmotic pressure P of dilute solutions ? (A) The equation is identical to that of ideal gas equation (B) The solute particles in solution are analogous to the gas molecules and the solvent is analogous to the empty space between the gas molecules (C) Solute molecules are dispersed in the solvent the way the gas molecules are dispersed in empty space (D) The equation is not identical to that of ideal gas equation 17. Which statements are correct about antifreeze mixtures to use to melt ice or snow on roads ? (A) Antifreeze mixture of CaCl2 + water (f.pt. – 500 C) is preferred over KCl + water (f.pt. – 100 C) (B) The low freezing point of aq. CaCI2 solution is due to its vant Hoff factor i = 3. (C) The use of antifreeze for salt solutions causes major problems of corrosion of steel car bodies and reinforcement bars in concrete road structures. (D) More is the amount of salt spreaded on road, easier is melting of ice. 18. The vapour pressure of a dilute solution of a solute is influenced by : (A) Temperature of solution (C) M.pt. of solute 19. (B) Mole fraction of solute (D) Degree of dissociation of solute In the depression of freezing point experiment , it is found that the : (A) Vapour pressure of the solution is less than that of pure solvent (B) Vapour pressure of the solution is more than that of pure solvent (C) Only solute molecules solidify at the freezing point (D) Only solvent molecules solidify at the freezing point 20. Which of the following statements are correct for van’t Hoff factor ‘i’ for a solution of weak electrolyte AxBy ? (A) i = 1 – a + Xa + Ya (B) i > 1 at normal dilution (C) i increases more rapidly with dilution and attains a limiting value of (x + y) at infinite dilution (D) The increase in ‘i’ with dilution is due to increase in molality of solution with dilution SOLUTION AND COLLIGATIVE PROPERTIES Part # II [Assertion & Reason Type Questions] Directions : Each question has 5 choices (A), (B), (C), (D) and (E) out of which only one is correct. (A) (B) (C) (D) (E) 1. Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1. Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1. Statement-1 is True, Statement-2 is False. Statement-1 is False, Statement-2 is True. Both Statements are False. Statement -1 : The molar mass obtained for benzoic acid in benzene is found to be nearly 244. Statement -2 : Benzoic acid has the formula HOOC COOH 2. Statement-1 : The difference in the boiling points of equimolar solution of HCl and HF decreases as their molarity is decreased. Statement-2 : The extent of dissociation decreases steadily with increasing dilution. 3. Statement-1 : When ‘a’ mL of a 0.1 molal urea solution is mixed with another ‘b’ mL of 0.1 molal glucose solution, the boiling point of the solution is no different from the boiling points of the samples prior to mixing but if ‘a’ mL of 0.1 molal urea is mixed with ‘b’ mL of 0.1 molal HF the boiling point of the mixture is different from the boiling points of the separate samples . Statement-2 : HF is an electrolyte (weak) whereas glucose is a non electrolyte. 4. Statement-I : 0.02 m solutions of urea and sucrose will freeze at same temperature. Statement-II : Freezing point of a solution is inversely proportional to the conc. of solution. 5. Statement-I : When mercuric iodide is added to the aqueous solution of KI, the freezing point is raised. 2– Statement-II : HgI2 reacts with KI forming complex ion [HgI4] . 6. Statement-I : 1 M solution of Glauber's salt is isotonic with 1 M solution of KNO3. Statement-II : Solutions having same molar concentration of solute may or may not have same osmotic pressure. 7. Statement-I : 0.1 M solution of NaCl has greater osmotic pressure than 0.1 M solution of glucose at same temperature. Statement-II : In solution, NaCl dissociates to produce more number of particles. 8. Statement-I : Relative lowering of vapour pressure is equal to mole fraction of the solvent. Statement-II : Relative lowering of vapour pressure is a colligative property. 9. Statement-I : Molal elevation constant depends on the nature of solvent. Statement-II : Molal elevation constant is the elevation in boiling point when 1 mole of the solute is dissolved in 1 kg of solvent. 10. Statement-I : If decimolal solution of sodium chloride boils at 101.2°C, then decimolal solution of calcium chloride will also boil at the same temperature. Statement-II : For same molal concentration of aqueous solutions of electrolytes, the elevation of boiling point may not be same. ANSWER KEY EXERCISE - 2 : PART # I 1. 7. 13. 19. A, B, C B, C, D B A, D 2. 8. 14. 20. A, B, C A B, C A, B, C 3. A, B 9. A, B 15. A, B, D 4. A, B, C 10. A, B, C 16. A, B, C 5. A, B, C, D 11. B 17. A, B, C, D PART # II 1. C 2. C 3. A 4. B 5. A 6. D 7. A 8. D 9. B 10. D 6. A, B, C, D 12. A, B 18. A, B, D