Use the following data to calculate the combined heat of hydration for the ions in potassium bromate

Problem Set 3: Solutions (Due on March 9. Leave your problem sets in my pigeonhole) 1. Predict which solvent will dissolve more of the given solute: a. Sodium chloride in methanol (CH3OH) or in 1-propanol (CH3CH2CH2OH). b. Ethylene glycol (HOCH2CH2OH) in hexane or in water. c. Diethyl ether (CH3CH2OCH2CH3) in water or in ethanol. 2. Which solute is more soluble in the given solvent? a. 1-Butanol (CH3CH2CH2CH2OH) or 1,4-butanediol (HOCH2CH2CH2CH2OH) in water. b. Chloroform (CHCl3) or carbon tetrachloride (CCl4) in water. 3. Water is added to a flask containing solid NH4Cl. As the salt dissolves, the solution becomes colder. a. Is the dissolving of NH4Cl exothermic or endothermic? b. Is the magnitude of Hlattice of NH4Cl larger or smaller than the combined Hhydration of the ions? Explain. c. Given the answer to a, why does NH4Cl dissolve in water? 4. Use the following data to calculate the combined heat of hydration for the ions in potassium bromate (KBrO 3): Hlattice = 745 kJ/mol Hsoln = 41.1 kJ/mol 5. State whether the entropy of the system increases or decreases in each of the following processes: a. Gasoline burns in a car engine. b. Gold is extracted and purified from its ore. c. Ethanol dissolves in 1-propanol. 6. You are given a bottle of solid X and three aqueous solutions of X one saturated, one unsaturated, and one supersaturated. How would you determine which solution is which? (Expain in no more than 3 sentences.) -3 7. The Henrys Law constant (k) for O2 in water at 20C is 1.28x10 mol/Latm. a. How many grams of O2 will dissolve in 2.00 L of H2O that is in contact with pure O2 at 1.00 atm? b. How many grams of O2 will dissolve in 2.00 L of H2O that is in contact with air, where the partial pressure of O 2 is 0.209 atm? 8. Calculate the molarity of each aqueous solution: a. 5.50 g of LiNO3 in 505 mL of solution. b. 25.0 mL of 6.15 M HCl diluted to 0.275 L with water. 9. Calculate the molality of the following: a. A solution containing 8.89 g of glycerol (C 3H8O3) in 75.0 g of ethanol (C2H5OH). b. A solution consisting of 34.0 mL of benzene ( = 0.877 g/mL) in 187 mL of hexane ( = 0.660 g/mL). 10. Calculate the molality, molarity and mole fraction of NH 3 in an 8.00% by mass aqueous solution ( = 0.9651 g/mL). 11. The crystal lattice energy for LiBr(s) is 818.6 kJ/mol at 25C. The hydration energies of the ions of LiBr is -867.4 kJ/mol at 25C. a. What is the heat of solution of LiBr(s) at 25C? + b. The hydration energy of Li (g) is -544 kJ/mol at 25C. What is the hydration energy for Br (g) at 25C? 12. a. Calculate the vapor pressure of water above a solution prepared by adding 22.5g of lactose (C 12H22O11) to 200.0g of water at 338K. The vapor pressure of water at 65C is 187.5 torr. b. Calculate the mass of propylene glycol (C3H8O2) that must be added to 0.340kg of water to reduce the vapor pressure of water (55.3 torr at 40C) by 2.88 torr at 40C. 13. a. Why does a 0.10m aqueous solution of NaCl have a higher boiling point than a 0.10m aqueous solution of C6H12O6? b. Calculate the boiling point of each solution. c. The experimental boiling point of the NaCl solution is lower than that calculated, assuming that NaCl is completely dissociated in solution. Why is this the case? 14. Using data from the attached table, calculate the freezing points and boiling points of each of the following solutions: a. 0.22m glycerol (C3H8O2) in ethanol; b. 0.240mol of naphthalene (C10H8) in 2.45mol of chloroform; c. 2.04g KBr and 4.82g glucose (C6H12O6) in 188g of water. 15. Lysozyme is an enzyme that breaks bacterial cell walls. A solution containing 0.150g of this enzyme in 210mL of solution has an osmotic pressure of 0.953 torr at 25C. What is the molar mass of lysozyme?Chem 14, PS3 Page 1 of 2

16. In a home ice cream freezer, we lower the freezing point of the water bath surrounding the ice cream can by dissolving NaCl in water to make a brine solution. A 15.0% brine solution is observed to freeze at 10.888C. What is the vant Hoff factor, i, for this solution? 17. For each of the following aqueous reactions, identify the acid, the base, the conjugate base and the conjugate acid: + a. H2O + H2CO3 H3O + HCO3 + + b. C5H5NH + H2O C5H5N + H3O c. HCO3 + C5H5NH H2CO3 + C5H5N 18. Place the species in each of the following pairs in order of increasing acid strength. Explain the order you chose for each pair. a. HIO3, HBrO3 b. HNO2, HNO3 c. HOCl, HOI 19. Identify the Lewis acid and Lewis base in each of the following reactions. + a. B(OH)3(aq) + H2O(l) B(OH)4 (aq) + H (aq) + b. Ag (aq) + 2NH3(aq) Ag(NH3)2(aq) c. BF3(g) + F (aq) BF4 (aq) 20. Some sulfuric acid is spilled on a lab bench. You can neutralize the acid by sprinkling sodium bicarbonate on it and then mopping up the resultant solution. The sodium bicarbonate reacts with sulfuric acid as follows: 2NaHCO3(s) + H2SO4(aq) Na2SO4(aq) + 2H2O(l) + 2CO2(g) Sodium bicarbonate is added until the fizzing due to the formation of CO 2(g) stops. If 27 mL of 6.0M H2SO4 was spilled, what is the minimum mass of NaHCO3 that must be added to the spill to neutralize the acid?

Table 1. Molal Boiling-Point-Elevation and Freezing-Point-Depression Constants Solvent Normal Boiling Point (C) Kb (C/m) Normal Freezing Point (C) Water, H2O 100.0 0.51 0.0 Benzene, C6H6 80.1 2.53 5.5 Ethanol, C2H5OH 78.4 1.22 -114.6 Carbon tetrachloride, CCl4 76.8 5.02 -22.3 Chloroform, CHCl3 61.2 3.63 -63.5

Kf (C/m) 1.86 5.12 1.99 29.8 4.68

Chem 14, PS3

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