2011, Robert Ayton. All rights reserved.

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1 Solutions Outline 1. Solubility 2. Concentration Calculations 3. Colligative Properties 4. Freezing Point Depression or Boiling Point Elevation Problems 5. Graphs of Colligative Properties Review 1. Solubility Raoult s Law Like Dissolves Like Gases - Henry s Law Solubility of a Gas is proportional to Gas Pressure; o High Pressure, Low Temperature = Higher Solubility of a Gas Solids and Liquids Increase Temperature (KE), Increase # of Surface Areas, Add a Catalyst, Add More Solvent will all Increase Solubility 2. Concentration Calculations 3. Colligative Properties Vapor Pressure is Lowered P A = P total x Mole Fraction Boiling Point Elevation Freezing Point Depression Osmosis = i MRT 4. Freezing Point Depression or Boiling Point Elevation Problems i = Van Hoff t Factor = # of particles in solution C 6 H 12 O 6 i = 1 NaCl i = 2 Na 2 SO 4 i = 3 Ca 3 (PO 4 ) 2 i = 5 5. Graphs of Colligative Properties

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3 Solutions Problem Set 1) Calculate the following without a calculator: a. The number of grams of solute to dissolve to make 250mL of 0.10 M KBr (FW = 120 g mol -1 ). b. The molar concentration (Molarity) of 29 grams of NaCl (MW = 58 g mol -1 ) dissolved in 500 ml of water. c. The amount in grams of CuSO 4 (Molar Mass =159) to make a 250 ml solution of 0.20 M. d. The molar concentration that results when 15 g of sodium iodide (FW = 150) is dissolve in 1.0 L of water. e. The new concentration when 10 ml of 2.0 M HCl is diluted with water to a new volume of 200 ml. 2) Which of the following in each pair is more likely to be more soluble in water? Give a short explanation. a. C 6 H 12 O 6 or C 6 H 6 b. HCl or HC 2 H 3 O 2 c. CH 3 COCH 3 or CH 3 CH 2 COOH d. CCl 4 or CaCl 2 e. KClO 3 at high temperatures or KClO 3 at low temperatures f. CO 2 at high temperatures or CO 2 at low temperatures 3) Explain the following: a. Why does soda need to be stored in sealed containers? Explain showing a chemical reaction. b. Why should you store an opened container of soda in the refrigerator? c. What are two things you could do to your iced tea mix to ensure it will fully dissolve in the water? 4) Calculate the following without a calculator: a. The molal concentration (molality) of 16 g of methanol (32 g mol -1 ) dissolved in 500 g of ethanol. b. The mole fraction of potassium chloride in a solution of 150 g of KCl (75 g mol -1 ) and 72 g of water. (18 g mol -1 ). c. The molal concentration of 39 g of benzene, C 6 H 6 (FW = 78), dissolved in 200 g of carbon tetrachloride, CCl 4 (FW = 152). d. The new vapor pressure of water if approximately 30 grams of NaCl (58 g mol -1 ) is dissolved in 9 grams of water. (P vap of pure water = 20 mmhg) e. The mass percentage the main ingredient in aspirin, acetylsalicylic acid when 20 g of acetylsalicylic acid is dissolved into 100 g of lauric acid. 5) List the following aqueous solutions in order of increasing boiling points: a m NaCl, 0.10 m glucose, 0.10 m Ca(NO 3 ) 2 b M C 6 H 12 O 6, M KBr, 0.50 M Cu(NO 3 ) 2 c m glycerin (C 3 H 8 O 3 ), m LiF, m Ca 3 (PO 4 ) 2 d m NaCl at 25 C, m LiBr at 50 C, m KF at 100 C 6) A solution of 0.64 g of adrenaline in 36.0 g of CCl 4 elevates the boiling point by 0.49 C. (K b of CCl 4 = 5.02) a. What is the molar mass of adrenaline? b. If the empirical formula of adrenaline is C 3 H 13 O 3, what is the molecular formula according to the colligative properties calculation?

4 7) A solution of 5.00 g of lauryl alcohol in 100 g of benzene freezes at 4.1 C. Pure benzene freezes at 5.5 C and has a K f value of 5.12 C/m. What is the approximate molar mass of lauryl alcohol? 8) Glycerin (C 3 H 8 O 3 ) has a density of 1.26 g/ml at 25. An ideal solution is made by adding 50.0 ml of glycerin to 500 ml of water (density of water is 1.00 g/ml). The vapor pressure of pure water at 25 C is 23.8 mmhg. a. Calculate the mole fraction of water. b. Calculate the vapor pressure of water for the solution. 9) A solution is made from 250 g of sodium chloride (NaCl) dissolved in 750 g of water. Calculate the freezing point of the solution. (K f of water is 1.86 C/m) 10) Calculate the freezing point decrease of a solution made by dissolving 42.0 g of C 10 H 18 O in 600 g of chloroform. (K f of chloroform is 4.68 K/m) 11) A solution was prepared by dissolving g of an unknown substance in 40 g of CCl 4. The boiling point of the resultant solution was C higher than that of the pure solvent. The boiling point elevation constant for carbon tetrachloride is 5.02 C kg/mol. Calculate the molar mass of the unknown substance. C 5 H 12 (g) + O 2 (g) CO 2 (g) + H 2 O (g) 12) The combustion of a hydrocarbon pentane, C 5 H 12 (molar mass = g), is shown above. a. Balance the reaction in the spaces provided above. b. Calculate the volume of dry carbon dioxide, measured at 25 C and 785 mmhg, will result from the complete combustion of 2.50 g of pentane. c. The complete combustion of 5.00 g of pentane releases 243 kj of heat. On the basis of this information, calculate the amount of heat for the complete combustion of one mole of pentane. d. A sample of unknown gas is found to effuse into a vacuum at twice the rate that a sample of pentane gas effuses. Calculate the molar mass of the unknown gas. 13) A g sample of solid lead (II) nitrate is added to 125 ml of M sodium iodide solution. Assume no change in volume of the solution. The chemical reaction that takes place is represented by the following reaction. Pb(NO 3 ) 2 (s) + 2 NaI (aq) PbI 2 (s) + 2 NaNO 3 (aq) a. List an appropriate qualitative observation that provides evidence of a chemical reaction between the two compounds. b. Calculate the number of moles of each reactant. c. Identify the limiting reactant. Show calculations to support your identification. d. Calculate the maximum mass in grams of the precipitate. 14) A g organic sample completely burns in O 2 (g) to produce g of CO 2 (g) and g of H 2 O (g). a. Calculate the individual masses of C, H, and O in the g organic sample. b. Determine the empirical formula of the organic sample. c. A g sample of the same organic compound was dissolved in g of lauric acid, and it was determined that the freezing point of lauric acid was lowered by 1.68 C. The value of K f for lauric acid is 3.90 C m -1. Assume that the sample does not dissociate in lauric acid. Calculate the molar mass of the organic sample.

5 d. Determine the molecular formula for the organic sample. e. Explain why the sample is not soluble in water. 15) The formula and the formula weight of an unknown hydrocarbon compound are determined by elemental analysis and by freezing-point depression. a. The hydrocarbon is found to contain 93.46% carbon. Calculate the empirical formula of the unknown hydrocarbon. b. A solution is prepared by dissolving 2.43 g of the unknown hydrocarbon in 26.7 g of naphthalene. The freezing point of pure naphthalene is determined to be 80.2 C while the solution is found to freeze at 76.2 C. The freezing point depression constant for naphthalene is 6.80 K m -1. Calculate the apparent molecular weight of the unknown hydrocarbon. c. What is the molecular formula of the unknown hydrocarbon?