FAC 0025, Trimester January 2013CHEMISTRY II (FAC0025) TUTORIAL 1 1. Look at following reactions and find which ones of them have solubility increasing with temperature. I. XY(s) + Heat → X2+(aq) + Y2II. XY2(s) → X2+(aq) + 2Y- (aq) + Heat III. XY3(s) → X3+(aq) + 3Y- (aq) + Heat 2. What is the order of solubility of NaCl in the following solvents; I. Pure water II. NaNO3(aq) III. Na2SO4(aq) 3. Why is it that ceric sulphate which is a solid inorganic salt becomes less soluble in water as the temperature increases? 4. Hydrogen sulfide, H2S, is a toxic gas responsible for the odor of rotten eggs. The solubility of H2S (g) in water at STP is 0.195 M. What is the solubility in water at 0oC and a partial pressure of 25 mm Hg. 5. The vapor pressure of pure water at 600C is 149 torr. The vapor pressure of water over a solution at 600C containing equal numbers of moles of water and ethylene glycol is 67 torr. Is the solution ideal in terms of Raoult’s law? Justify your answer. 6. At 63.50C, the vapor pressure of H2O is 175 torr, and that of ethanol, C2H5OH, is 400 torr. A solution is made by mixing equal masses of H2O and C2H5OH. (a) What is the mole fraction of ethanol in the solution? (b) Assuming ideal-solution behavior, what is the vapor pressure of the solution at 63.50C? (c) What is the mole fraction of ethanol in the vapor pressure above the solution? 7. Lactose, C12H22O11, is a naturally occurring sugar found in mammalian milk. A 0.335 M solution of lactose in water has a density of 1.0432 g/mL at 20oC. Calculate: (a) the mole fraction, (b) the mass percentage, (c) the molality of the solution. 1 FAC 0025, Trimester January 2013 8. Using data from Table Q8, calculate the freezing and boiling points of each of the following solutions. (a) 0.17 m glycerol in ethanol (b) 1.92 mol of naphthalene, C10H8, in 16.8 chloroform (c) 5.44 g KBr and 6.35 g glucose, C6H12O6, in 200 g of water Table Q8 Solvent Normal Boiling Point (0C) Kb (0C/m) Normal Freezing Point (0C) Kf (0C/m) Water, H2O 100.0 0.52 0.0 1.86 Benzene, C6H6 80.1 2.53 5.5 5.12 Ethanol, C2H5OH 78.4 1.22 -114.6 1.99 Carbon tetrachloride, CCl4 76.8 5.02 -22.3 29.8 Chloroform, CHCl3 61.2 3.63 -63.5 4.68 9. Lysozyme is an enzyme that breaks bacterial cell walls. A solution containing 0.150 g of this enzyme in 210 mL of solution has an osmotic pressure of 9.53 torr at 25 0C. What is the molar mass of this substance? 10. (a) Calculate how much strontium fluoride will dissolve in 1 L of water given Ksp = 2.5 x 10-9 at 25oC. (b) Chemical analysis gave [Sr2+] = 0.012 M, and [F-] = 0.024 M in a solution. Is the solution saturated, supersaturated or unsaturated? (c) Will a precipitate form if 0.100 L of 0.30 M Ca(NO3)2 is mixed with 0.200 L of 0.060 M NaF? (Ksp for CaF2 at 25oC is 3.2 x 10-11) 11. (a) Write an expression for the solubility product, Ksp, of calcium hydroxide, Ca(OH)2. (b) In a titration experiment in the chemistry laboratory, 20.0 cm3 of an aqueous calcium hydroxide solution is completely neutralised by 18.2 cm3 of hydrochloric acid solution with a molar concentration of 0.050 moldm-3. (i) Determine the hydroxide ion concentration. (ii) Calculate the solubility product of calcium hydroxide. (iii) State one use of calcium hydroxide which depends on its solubility in water. 12. Estimate the solubility of barium sulfate in a 0.020 M sodium sulfate solution. The solubility product constant for barium sulfate is 1.1 x 10-10. 2