Thermodynamics - Assignment 4 (Solutions & Colligative properties) 1. What is the difference between molar volume and partial molar volume? Under what condition are they equal? 2. Define Raoult’s law and Henry’s law? What are ideal solutions and ideal dilute solutions? 3. What type of liquids show ideal behavior? What type of liquids show positive and negative deviations? 4. Derive a relation between depression of freezing point and molar mass of solute? 5. What is van’t Hoff factor for electrolytic solutions? Derive a relation between van’t Hoff factor and degree of dissociation of a weak electrolyte. 6. Write a short note on molar mass determination using colligative properties. 7. 0.2 moles of glucose are dissolved in 1L of water and same amount is dissolved in 1L benzene. Will elevation in boiling point be same for both solutions? Give reason. 8. 0.1 mole of glucose is dissolved in 1L water. In another solution 0.1 mole of urea is dissolved in 1L of water. Will the depression in freezing point be same for both solutions? Give reason. 9. Molar mass of benzoic acid was determined by osmotic pressure determination for solutions in water and in benzene. The molar mass was found to be different in both the cases. Explain. 10. A 0.1M solution of glucose and same concentration of NaCl in water will have equal or different elevation in boiling point? Explain. 11. 0.1M solution of NaCl in water and 0.1M solution of acetic acid in water will have same or different elevation in boiling point? Explain. 12. What will happen if a cell is placed in a solution of NaCl? 13. What will happen if a cell is placed in deionized water? 14. A mixture of NaCl and ice is used for storing ice cream. Explain. 15. In cold countries salt is sprinkled on roads covered with snow to clear them. Explain. 16. What weight of glycerol would have to be added to 1000 gram of water in order to lower its -1 freezing point by 10K? Freezing point depression constant Kf for water is 1.86 Kkgmol . 17. An aqueous solution contains 20 grams of glucose per L. Calculate its osmotic pressure at 298K. 18. An aqueous solution freezes at 271.5K. Calculate its normal boiling point and vapor pressure -1 -1 at 298K if Kf (water) = 1.86 K.Kgmol and Kb (water) = 0.51 K.Kgmol . -1 19. 2g of benzoic acid dissolved in 25g of benzene, Kf = 4.90K.kgmol , produce a freezing point depression of 1.62K. Calculate the molar mass of benzoic acid. 20. The heat of fusion of acetic acid is 11.72kJmol-1 at its melting point is 16.6 ˚C. Calculate its cryoscopic constant. 1 21. 30g of sucrose (C12H22O11) and 30g of glucose (C6H12O6) were dissolved in 804g of water. What is the vapor pressure of this solution at 303K, if the vapor pressure of water is 31.82 mmHg. 22. The boiling point of ethyl alcohol is 78.4˚C and its heat of vaporization is 39.42kJmol-1 calculate the molal boiling point elevation constant for ethyl alcohol. 23. Pure benzene freezes at 5.4˚C and a solution of 0.223g of phenyl acetic acid (C6H5CH2COOH) in 4.4g benzene freezes at 4.47˚C. The molar enthalpy of fusion of benzene is 9.89kJmol-1. Calculate the apparent molar mass phenyl acetic acid and comment on its form in the solution. 24. The chemical potential of pure water -285.84kJmol-1. What is the chemical potential of water in a solution containing 0.1 mole of a solute in 120g of water at 298K and 1 atm . 25. The freezing point of a solution of 0.138g of a nonvolatile solute in 15.2g benzene is 0.53K less than the freezing point of pure benzene. What are the molar mass of the substance and -1 -1 the normal boiling point of the solution. Kf=5.082Kkgmole and Kb=2.53Kkgmole and freezing point of pure benzene is 800C. 26. The vapor pressure of a solution of urea is 736.2 mmHg at 100˚C. What is the osmotic pressure of this solution at 15˚C. 27. An aqueous solution contains 5% by mass of urea, 1% by mass of KCl and 10% by mass of glucose. Calculate its freezing point assuming complete ionization of KCl. (Kf for water = 1.86 KKgmol-1). 28. 1.25g of benzoic acid when dissolved in 100 mL of benzene produces osmotic pressure of 1.73 atm at 300K. Calculate the %age of benzoic acid in dimerised state. 29. Is the lowering of chemical potential of a solvent in an ideal solution an enthalpy effect or an entropy effect? Explain. 30. Why is the boiling point of a solution greater than of a pure solvent? 31. In an infinitely dilute solution of NaCl in water, the van’t Hoff factor is equal to two but in a concentrated solution it is less than two. Explain. 32. The van’t Hoff factor for a solution of acetic acid in water depends on the concentration of the solution. Explain. 33. A mixture of toluene and benzene contains 35% by weight of toluene. At 30˚C the vapor pressure of pure benzene is 118.2mmHg and of toluene is 36.7 mmHg. Calculate total pressure and partial pressure of each component. 34. A 0.2 molal aqueous solution of KCl freezes at -0.68˚C. Calculate van’t Hoff factor and the -1 osmotic pressure at 0˚C if the Kf for water is1.86K kgmol . 35. A metal M(Atomic Mass ═ 96) reacts with F(Atomic Mass ═ 19) to form MFx. When 9.18g sample of salt was dissolved in 100g water the boiling point of solution was 374.38K. What -1 is the formula of the salt given Kb ═ 0.512Kkgmol and normal boiling point of water is 373.15K. 36. Why does a salt solution fail to quench thirst? Explain. 2 37. A 10m solution of Urea is cooled to -14.88˚C. What mass of Urea will separate out if 100g -1 solution is taken? Kf(Water) ═ 1.86Kkgmol . 3 .