AP ChemistryName :
Worksheet 11-3Date :
A. Multiple choice : Calculators may not be used on the multiple choice.
_____ 1. Which of the following will be lower for a 1.0 molar concentration of any type of solute in pure water?
I. freezing point II. pH III. electrical conductivity IV. Absorption of light V. vapor pressure
a. I b. I and V c. I and III d. III and IV e. V
_____ 2. The vapor pressure above a solution at 25 ºC is 19.04 torr. What is the mole fraction of glucose in the solution? (Vapor pressure of water at 25 ºC is 23.8 torr)
a. 0.80 b. 0.60 c. 0.40 d. 0.20 e. 0.10
_____ 3. 20.0 mL of a 0.40 M solution of sodium carbonate is added to 20.0 mL of a 0.50 M solution of calcium nitrate. What is the resulting concentration of calcium ions in the mixture?
a. 0.025 M b. 0.050 M c. 0.010 M d. 0.020 M e. 0.030 M
_____ 4. A 10.0 gram sample of a certain compound contains only one sulfur atom per molecule of the substance. The substance was treated to oxidize all the sulfur atoms to sulfate ions and then an excess of sulfuric acid was added to precipitate out all of the sulfate as barium sulfate. If the mass of barium sulfate ( FW = 233.40) was 28.5 grams, what is the molar mass of the compound?
a. 20.5 g/mol b. 45.6 g/mol c. 81.9 g/mol d. 122 g/mol e. 165 g/mol
… Cd + … H+ + … NO3-… Cd2+ + … NO + … H2O
_____ 5. The above reaction occurs in acidic solution. What is the coefficient in the balanced reaction for the element Cd?
a. 1 b. 2. c. 3 d. 4 e. 5
7 CN- + 2 OH- + 2 Cu(NH3)42+ --> 2 Cu(CN)32- + 8 NH3 + CNO- + H2O
_____ 6. The oxidizing agent in the above reaction is
a. CN- b. OH- c. Cu2+ d. NH3 e. this is not a redox reaction
_____ 7. Carbon disulfide can be oxidized to form carbon dioxide and sulfur dioxide. How many liters of oxygen (at STP) are needed to oxidized 19.0 grams of carbon disulfide?
a. 60.0 L b. 48.4 L c. 72.6 L d. 12.1 L e. 16.8 L
_____ 8. For the above reaction, what volume of carbon disulfide can be oxidized by 30.0 L of oxygen at the same conditions of temperature and pressure?
a. 30.0 L b. 15.0 L c. 20.0 L d. 10.0 L e. 5.00 L
_____ 9. The solubility of oxygen gas at 25 ºC and one atm of pressure is 8.6 mg/L. What will the solubility be at 2.5 atm and the same temperature?
a. 22 mg/L b. 26 mg/L c. 30.0 mg/L d. 38.0 mg/L e. 12.2 mg/L
10. Pentane (C5H12) and hexane (C6H14) form an ideal solution. At 25°C the vapor pressures of pentane and hexane are 511 and 150. torr, respectively. A solution is prepared by mixing 75 mL pentane (density, 0.63 g/mL) with 75 mL hexane (density, 0.66 g/mL).
a. What is the vapor pressure of the resulting solution?
b. What is the composition by mole fraction of pentane in the vapor that is in equilibrium with this solution?
11. What is the osmotic pressure of a solution formed by dissolving 125 grams of sucrose(C12H22O11) in enough water to form 825 mL of solution at 25 ºC?
12. Place the following solutions in order by the decreasing size of the freezing-point depression.
a. 1.0 m glucose in water (Glucose is a nonelectrolyte.)
b. 1.0 m NaCl in water
c. 1.0 m HOC1 in water (HOC1 is a weak acid.)
d. 1.0 m MgCl2 in water
13. From the following:
pure water
solution of C6H12O6(X = 0.01) in water
solution of NaCl (X =0.01)in water
solution of CaCl2(X =0.01)in water
choose the one with the
a. highest freezing point.
b. lowest freezing point.
c. highest boiling point.
d. lowest boiling point.
e. highest osmotic pressure.
14. Calculate the freezing point and the boiling point of each of the following solutions. (Assume complete dissociation.)
a. 5.0 g NaCl in 25 g H2O
b. 2.0 g A1(NO3)3 in 15 g H2O
15. Use the following data for three aqueous solutions of to calculate the apparent value of the van't Hoff factor.
Molality Freezing-Point Depression (°C)
0.02250.110
0.09100.440
0.2781.330
16. Calculate the osmotic pressure at 25°C of a 0.50 M solution of Ca(NO3)2 in water. (Assume that i = 3.0.) Would you expect the measured osmotic pressure of 0.50 M Ca(NO3)2 to be higher or lower than the value you calculated? Explain.
17. An aqueous antifreeze solution is 40.0% ethylene glycol (C2H6O2) by mass. The density of the solution is 1.05 g/cm3. Calculate the molality, molarity, and mole fraction of the ethylene glycol.
18. In flushing and cleaning columns used in liquid chromatography to remove adsorbed contaminants, a series of solvents is used. Hexane (C6H12), chloroform (CHCl3), methanol (CH3OH), and water are passed through the column in that order. Rationalize the order in terms of intermolecular forces and the mutual solubility (miscibility) of the solvents.
19. Is Henry's law (Henry’s law : The solubility of a gas is directly proportional to the partial pressure of the gas above the solution.” valid for the solubility of CO2 in a 0. 1 M NaOH solution? Hint: CO2 + OH- HCO3-
20. At a certain temperature, the vapor pressure of pure benzene (C6H6) is 0.930 atm. A solution was prepared by dissolving 10.0 g of a nondissociating, nonvolatile solute in 78.11 g of benzene at that temperature. The vapor pressure of the solution was found to be 0.900 atm. Assuming the solution behaves ideally, determine the molar mass of the solute.
21. An unknown compound contains only carbon, hydrogen, and oxygen. Combustion analysis of the compound gives mass per-cents of 31.57% C and 5.30% H. The molar mass is determined by measuring the freezing-point depression of an aqueous solution. A freezing point of -5.20°C is recorded for a solution made by dissolving 1 0.56 g of the compound in 25.0 g water. Determine the empirical formula, molar mass, and molecular formula of the compound. Assume that the compound is a nonelectrolyte.
22. A 0.15-g sample of a purified protein is dissolved in water to give 2.0 mL of solution. The osmotic pressure is found to be 18.6 torr at 25°C. Calculate the protein's molar mass.
23. A 1.60-g sample of a mixture of naphthalene (C10H8 FW = 128.2g) and anthracene (C14H10 FW = 178.2g) is dissolved in 20.0 g benzene (C6H6). The freezing point of the solution is 2.81°C. What is the composition as mass percent of the sample mixture? The freezing point of benzene is 5.51°C, and Kfis 5.12°C • kg/mol.
24. Formic acid (HCO2H) is a monoprotic acid that ionizes only partially in aqueous solutions. A 0.10 M formic acid solution is 4.2% ionized. Assuming that the molarity and molality of the solution are the same, calculate the freezing point and the boiling point of 0.10 M formic acid. (HCO2H ↔ H+ + CO2H- ; calculate total M by adding species in solution – watch sig figs)
25. Explain how you would, in a laboratory, do the following:
a. Separate a powdered mixture of barium sulfate and sodium acetate.
b. Separate a mixture of two volatiule liquids.
Answers : 10a. 341 torr 10b. Xpent = 0.79, Xhex = 0.21 11. 10.8 atm 12. d>b>c>a 13. a. pure water b. CaCl2 c. CaCl2 d. pure water e. CaCl2 14a. b.p. = 103.5 ºC, f.p. = - 13 ºC 14b. b.p. = 101.3 ºC, f.p. = - 4.7 ºC 15. i = 2.63 for 0.0255 m CaCl2, i = 2.60 for 0.0910 m CaCl2, i = 2.57 for 0.0278 m CaCl2 –note the van’t Hoff factor is less than the ideal value of 3 due to ion pairing. 16. π = 37 atm. The expected osmotic pressure would be lower due to ion pairing. 17. m = 10.7, M = 6.77, Xeth. Gly = 0.162 19. No the reaction indicated would greatly increase the solubility of carbon dioxide by forming the soluble bicarbonate ion. 20. 3.0 x 102 g/mol 21. 151 g/mol (calculated - 152.10 actual) 22. 7.5 x 104 g/mol 23. 44% naphthalene, 56% anthracene 24. b.p. = 100.056 ºC, f.p. = -0.20 ºC