LR 12 05 and 08 2014 1 Methane has a Henry s Law constant of 9 88 10 2 mol L atm when dissolved in benzene at 25 C How many grams of CH4 will dissolve in 3 00 L of benzene if the partial pressure of CH4 is 1 48 atm c kP 9 88 10 2 mol L atm 1 48atm 0 146 mol L 0 146 mol x 16 0g x 3 00L 7 02 g CH4 1 00L 1 mol 2 Calculate the molarity and the molality of a 15 0 by mass solution of MgCl2 in H2O The density of this solution is 1 127 g mL Assume 100 g of solution 15 0g is MgCl2 and 85 0g is water Molarity mol L 15 0g MgCl2 x 1 mol MgCl2 0 158 mol MgCl2 95 2g MgCl2 100g of solution x 1 00 mL 88 7 mL 0 0887L 1 127 g Molarity 0 158 mol 0 0887 L of solution Molality mol kg of solvent 3 1 78 M 0 158 mol 0 085 kg water 1 86 m What is the vapor pressure of a solution at 30 C that contains 398 g of sucrose C12H22O11 in 524 g of water The vapor pressure of water at 30 C is 31 8 mm mol of sucrose 398g x 1mol 1 16 mol 342 g mol of water 524g x 1 mol 29 1 mol 18 g Total number of mol 30 3 mol Xwater 29 1 mol 0 960 30 5 mm Pvapor 0 960 31 8mm 1 30 3 mol 4 A solution is made of ethanol and 1 propanol At 35 C the vapor pressure of ethanol is 100 mmHg and of 1 propanol is 38 0 mmHg Calculate the partial pressure of each component if the mole fraction of ethanol is 0 300 If the mole fraction of ethanol is 0 300 then the mole fraction of 1 propanol is 0 700 Pethanol 0 300 100mmHg 30 0 mmHg P1 propanol 0 700 38 0mmHg 26 6 mmHg 5 How many grams of ethylene glycol molar mass 62 1 g mol should be added to 6 50 kg of water the amount in a car radiator to lower the freezing point to 22 0 C Kf for water is 1 86 C m Tf Kfm m Tf 22 0 C 11 8 m Kf 1 86 C m 11 8 mol x 6 50 kg x 62 1 g 4 77 x 103g 1 kg 1 mol 6 How many grams of glycerol C3H5 OH 3 molar mass 92 0 g mol should be added to 100g of water to form a solution that boils at 107 C Kb for water is 0 52 C m Tb Kbm m Tb 7 0 C 13 5 m Kb 0 52 C m 13 5 mol x 0 100 kg x 92 0 g 124g 1 kg 1 mol 7 What are the boiling and freezing point of a 2 47m solution of naphthalene dissolved in benzene The boiling point of benzene is 80 1 C its freezing point is 5 50 C Kb is 2 53 C m and Kf is 5 12 C m Tb 2 53 C m 2 47m 6 25 C Boiling point 80 1 C 6 25 C 86 3 C Tf 5 12 C m 2 47m 12 6 C 2 Freezing point 5 50 C 12 6 C 7 10 C 8 Which of the following solutions would have the lowest boiling point sugar solution Lowest freezing point MgSO4 1 00 m sugar solution 1 00 m NaCl 2 00 m ethylene glycol 2 00 m MgSO4 9 An aqueous solution of ascorbic acid vitamin C contains 22 0 g of ascorbic acid in 100g of water This solution freezes at 2 33 C What is the molar mass of ascorbic acid Tf Kfm m Tf 2 33 C 1 25 m Kf 1 86 C m 1 25 mol x 0 100kg 0 125 mol 1kg 10 22 0g 176g mol 0 125 mol Of the substances listed below which should have the lowest vapor pressure The substance that has the highest concentration of particles KCl The lowest boiling point The one with the fewest number of particles ethylene glycoL The lowest freezing point The one with the most number of particles KCl Which two solutions should have the same freezing point urea and CaCl2 a b c d 1 50 m urea solution 1 50mol kg 1 50 mol particles 0 75 m ethylene glycol 0 75 mol kg 0 75 mol particles 1 20 m KCl 1 20mol kg x 2 ions formula unit 2 4 mol particles 0 50 m CaCl2 0 50mol kg x 3 ions formula unit 1 5 mol particleS 3 4
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