Ch 12 and 13 Practice Problems

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1 Ch 12 and 13 Practice Problems The following problems are intended to provide you with additional practice in preparing for the exam. Questions come from the textbook, previous quizzes, previous exams, and other sources. A solutions manual is supplied in a separate document. 1. Which of the following has the substances in order of decreasing boiling point? CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 OH HOCH 2 CH 2 OH CH 3 CH 2 CH 2 Cl 2. What property of water allows a needle to float on it without sinking? 3. The scent wintergreen includes methyl salicylate (C 8 H 8 O 3 ) and has a vapor pressure of 2.52 mm Hg at 70 C. The vapor pressure at 100 C is 12.8 mm Hg. Calculate the vapor pressure of methyl salicylate at 154 C. 4. A g sample of CO 2 was compressed into a 2.61 L flask at 10.0 C. Which answer correctly reflects the contents of the flask? You may find the phase diagram at the right helpful. (The density of CO 2(l) at 10 C and 10 atm is 0.77 g/ml.) A. Solid only B. Liquid only C. Gas only D. A mixture of solid and liquid E. A mixture of solid and gas F. A mixture of liquid and gas 5. Answer the following questions, regarding the following two series of compounds. I. CH 3 OH Xe CCl 4 PF 3 II. Cl 2 H 3 PO 4 CH 3 Br CH 2 F 2 a. For each series, place in order of increasing inter-molecular forces. b. For each series, which will have the highest vapor pressure at 25 C?

2 6. Fractional distillation is used to separate the various hydrocarbons in crude oil. You set up a fractional distillation where g of ortho-xylene was combined with g of para-xylene yielding a homogeneous mixture in your distillation apparatus. You heat the liquid to 120 C. What is the mole fraction of para-xylene in the vapor as it enters the fractionating column? o-xylene p-xylene molecular formula C 8 H 10 C 8 H 10 density (g/ml) Normal b.p. ( C) P vap (120 C), mmhg H vap (kj/mol) For the following compounds, place an X in the box for all of the intermolecular forces present for that compound. Hydrogen bonding Dipole-dipole London Forces H 3 C-CCl 3 1-octanol SO 2 N 2 oxalic acid b. Which will have the highest boiling point? 8. Calculate the enthalpy of vaporization (ΔH vap in kj/mol) of diethyl ether which has a normal boiling point of 34.6 C and atm at 25.0 C.

3 9. For the following combinations of substances, determine if a homogenous mixture would be observed. Will the solid be soluble in the solvent? Will the two liquids be miscible or immiscible (not miscible)? Justify your answer inside each box to the right. Cmpd 1 Cmpd 2 Homogeneous (Y/N) Justification a. Br 2(s) CHCl 3(l) b. C 5 H 12 C 2 Cl 4 c. acetone H 2 O d. C 5 H 12 H 2 O e. 0.05g NaCl f. 0.50g NaCl 100 ml CH 3 OH 10 ml C 5 H The freezing point of an aqueous solution prepared with 176 g H 2 O was determined to be 5.02 C after g of a soluble, unknown ionic solid was added. Which ionic compound was added: sodium nitrate (85 g/mol) or sodium phosphate (196 g/mol)? Support your choice with a calculation. 11. Calculate the total heat (in Joules) needed to convert g of H 2 O (s) at C to H 2 O (l) at 47.2 C. H 2 O (s) H 2 O (l) C sp (J/g C) density (g/ml) Place the following in order of increasing kj/mol. a) ΔH vap (H 2 O) b) ΔH vap (F 2 ) c) ΔH vap (GeH 4 ) d) ΔH fus (CH 2 Cl 2 )

4 13. Calculate the vapor pressure of ortho-xylene and para-xylene, C 8 H 10, at 87 C. Report your answer in mm Hg. o-xylene p-xylene molecular formula C 8 H 10 C 8 H 10 density (g/ml) Normal b.p. ( C) P vap (120 C), mmhg H vap (kj/mol) A 154 cm 3 ice cube at C is added to a thermally isolated container with ml H 2 O (l) at 30.0 C. What mass (in grams) of ice remains in the container after thermal equilibrium is reached? H fus =6.01 kj/mol) H 2 O (s) H 2 O (l) C sp (J/g C) density (g/ml) Place the following solution in order of increasing freezing point m sucrose m AgNO m CuSO m MgCl Consider a three component mixture containing ml water, ml ethanol and g sucrose (C 12 H 22 O 11, g/mol). Calculate the mole fraction of ethanol in the vapor above this solution at 50 C. H 2 O EtOH molar mass (g/mol) density (g/ml) Normal b.p. ( C) P vap (50 C), mmhg H vap (kj/mol) An experiment was conducted with a sealed container of ethanol and varying temperature. Ethanol (C 2 H 6 O, 1.41 g) was added to a 5.6 L bottle that was sealed, evacuated to remove any air, and placed in an ice bath containing H 2 O (l) and H 2 O (s). Eventually the vapor pressure inside the flask stabilized at 0 C. (normal b.p. = 78.4 C, normal f.p. = -114 C, ΔH vap = kj/mol) a. What mass of ethanol was in the vapor phase at 0 C? b. What mass of ethanol was in the liquid phase at 0 C? c. The bottle was placed in a beaker of boiling water. What was the vapor pressure inside the bottle in the beaker of boiling water?

5 18. For the following two molecules, one is soluble in water and the other is soluble in hexane. Which is soluble in water and which is soluble in hexane. Explain the difference in solubility between the two compounds. a. Nonanoic acid b. glucose 19. The solubility of caffeine in water varies with temperature. At room temperature its solubility is 2 g/ 100 ml while at 100 C the solubility is 66 g/ 100 ml. Explain this difference. A cup of coffee can contain 95 mg of caffeine per 8 oz. Is the solution saturated, unsaturated or super saturated in caffeine? 20. An aqueous solution was prepared by g lithium carbonate dissolving in g H 2 O. Answer the following question regarding this solution. a. Calculate the molality b. Calculate the mole fraction of H 2 O. c. Calculate the percent mass of lithium carbonate. d. Calculate the vapor pressure above the solution at 45 C. (P H2O = 71.9 mmhg at 45 C) e. Calculate the boiling point of the solution. 21. Calculate the total pressure at 50 C above a mixture of methanol (CH 3 OH) and acetic acid (C 2 H 6 O 2 ) where the masses used of each compound are the same but of sufficient quantity that both compounds are present as both liquids and vapors. (P CH3OH = 400 mmhg at 50 C and P C2H4O2 = mmhg at 50 C).

2. What property of water allows a needle to float on it without sinking? Answer: surface tension

2. What property of water allows a needle to float on it without sinking? Answer: surface tension Ch 12 and 14 Practice Problems - KEY The following problems are intended to provide you with additional practice in preparing for the exam. Questions come from the textbook, previous quizzes, previous