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Learning Log -Solutions-2010/11 I. PROBLEMS: Solve the following problems. Show all work concentration problems (31, 35a , 37a) vapor pressure (47) freezing and boiling points (51) Molar Mass from osmotic pressure (61) Molar Mass by freezing point depression(59) II. CONCEPTS: Explain the following concepts and give an example a). Solution Process-- explain the solute-solvent interactions that cause polar and ionic solutes to dissolve in a polar solvent like water and nonpolar solutes to dissolve in nonpolar solvents like CCl4. Answer question 3 b) What happens to the following colligative properties of a liquid when a non-volatile solute is added: 1) vapor pressure 3) freezing point 2) boiling point 4) osmotic pressure PROBLEM: The formula and the molecular weight of an unknown hydrocarbon compound are to be determined by elemental analysis and the freezing point depression method. a) The hydrocarbon is found to contain 93.46 % carbon and 6.54 % hydrogen. Calculate the empirical formula of the unknown hydrocarbon. b) A solution is prepared by dissolving 2.53 grams of p-dichlorbenzene (MM=147.0) in 25.86 g of naphthalene (MM = 128.2) . Calculate the molality of the p-dichlorobenzene solution. c) The freezing point of pure naphthalene is determined to be 80.2oC The solution prepared in “b” is found to have an initial freezing point of 75.7oC. Calculate the molal freezing point constant of naphthalene. d) A solution of 2.43 grams of the unknown hydrocarbon is dissolved in 26.7 g of naphthalene is found to have an initial freezing point of 75.7oC. Calculate the apparent molecular weight of the unknown hydrocarbon on the basis of the freezing point depression experiment above. e) What is the molecular formula of the unknown hydrocarbon?