(a) What is the molality of a solution formed by dissolving 1 .25 mol ofKCl in 16.0 mol

This figure shows the interaction of a cation with surrounding water molecules. Would you expect the energy of ion-solvent interaction to be greater for Na+ or Li+ ? Explain. [Section 13.1]

Why do ionic substances with higher lattice energies tend to be less soluble in water than those with lower lattice energies? [Section 13.1]

Rank the contents of the following containers in order of increasing entropy: [Section 13.1]

A quantity of the pink solid on the left in Figure 13.8 is placed in a warming oven and heated for a time. It slowly turns from pink to the deep blue color of the solid on the right. What has occurred? [Section 13.1]

Which of the following is the best representation of a saturated solution? Explain your reasoning. [Section 13.2]

The solubility of Xe in water at 20 oc is approximately 5 X 10-3 M. Compare this with the solubilities of Ar and Kr in water (Table 13.2) and explain what properties of the rare gas atoms account for the variation in solubility. [Section 13.3]

The structures of vitamins E and B6 are shown below. Predict which is largely water soluble and which is largely fat soluble. Explain. [Section 13.3]

If you wanted to prepare a solution of CO in water at 25 oc in which the CO concentration was 2.5 mM, what pressure of CO would you need to use? (See Figure 13.18.) [Section 13.3]

The figure shows two identical volumetric flasks containing the same solution at two temperatures. (a) Does the molarity of the solution change with the change in temperature? Explain. (b) Does the molality of the solution change with the change in temperature? Explain. [Section 13.4]

Suppose you had a balloon made of some highly flexible semipermeable membrane. The balloon is filled completely with a 0.2 M solution of some solute and is submerged in a 0.1 M solution of the same solute: Initially, the volume of solution in the balloon is 0.25 L. Assuming the volume outside the semipermeable membrane is large, as the illustration shows, what would you expect for the solution volume inside the balloon once the system has come to equilibrium through osmosis? [Section 13.5]

The molecule n-octylglucoside, shown here, is widely used in biochemical research as a nonionic detergent for "solubilizing" large hydrophobic protein molecules. What characteristics of this molecule are important for its use in this way? [Section 13.6]

In general, the attractive intermolecular forces between solvent and solute particles must be comparable or greater than solute-solute interactions for significant solubility to occur. Explain this statement in terms of the overall energetics of solution formation.

(a) Considering the energetics of solute-solute, solventsolvent, and solute-solvent interactions, explain why NaCI dissolves in water but not in benzene (C6H6) (b) What factors cause a cation to be strongly hydrated?

Indicate the type of solute-solvent interaction (Section 11.2) that should be most important in each of the following solutions: (a) CCI4 in benzene (C6H6), (b) methanol (CH30H) in water, (c) KBr in water, (d) HCI in acetonitrile (CH3CN).

Indicate the principal type of solute-solvent interaction in each of the following solutions, and rank the solutions from weakest to strongest solute-solvent interaction: (a) KCI in water, (b) CHzClz in benzene (C6H6), (c) methanol (CH30H) in water.

(a) In Equation 13.1 which of the energy terms for dissolving an ionic solid would correspond to the lattice energy? (b) Which energy terms in this equation are always exothermic?

The schematic diagram of the solution process as the net sum of three steps in Figure 13.4 does not show the relative magnitudes of the three components because these will vary from case to case. For the dissolution of N03 in water, which of the three enthalpy changes would you expect to be much smaller than the other two? Explain.

When two nonpolar organic liquids such as hexane (C6H14) and heptane (C7H16l are mixed, the enthalpy change that occurs is generally quite small. (a) Use the energy diagram in Figure 13.4 to explain why. (b) Given that t.Hsoln "' 0, explain why hexane and heptane spontaneously form a solution.

The solubility of Cr(N03h 9 HzO in water is 208 g per 100 g of water at 15 oc. A solution of Cr(N03h 9 H20 in water at 35 oc is formed by dissolving 324 g in 100 g water. When this solution is slowly cooled to 15 C, no precipitate forms. (a) What term describes this solution? (b) What action might you take to initiate crystallization? Use molecular-level processes to explain how your suggested procedure works.

The solubility of Mn504 H20 in water at 20 oc is 70 g per 100 mL of water. (a) Is a 1.22 M solution of Mn504 H20 in water at 20 oc saturated, supersaturated, or unsaturated? (b) Given a solution of Mn504 H20 of unknown concentration, what experiment could you perform to determine whether the new solution is saturated, supersaturated, or unsaturated?

By referring to Figure 13.17, determine whether the addition of 40.0 g of each of the following ionic solids to 100 g of water at 40 oc will lead to a saturated solution: (a) NaN03, (b) KCI, (c) KzCrz07, (d) Pb(N03)z.

By referring to Figure 13.17, determine the mass of each of the following salts required to form a saturated solution in 250 g of water at 30 C: (a) KC103, (b) Pb(N03)z, (c) Cez(S04)3.

Water and glycerol, CH2(0H)CH(OH)CH20H, are miscible in all proportions. What does this mean? How do the OH groups of the alcohol molecule contribute to this miscibility?

Oil and water are immiscible. What does this mean? Explain in terms of the structural features of their respective molecules and the forces between them.

(a) Would you expect stearic acid, CH3(CH2h6COOH, to be more soluble in water or in carbon tetrachloride? Explain. (b) Which would you expect to be more soluble in water, cyclohexane or dioxane? Explain.

Consider a series of carboxylic acids whose general formula is CH3(CHz)nCOOH. How would you expect the solubility of these compounds in water and in hexane to change as n increases? Explain.

Which of the following in each pair is likely to be more soluble in hexane, C14: (a) CC4 or CaClz; (b) benzene (C6H6) or glycerol, CH2(0H)CH(OH)CH20H; (c) octanoic acid, CH3CH2CH2CH2CH2CH2CH2COOH, or acetic acid, CH3COOH. Explain your answer in each case.

(a) Explain why carbonated beverages must be stored in sealed containers. (b) Once the beverage has been opened, why does it maintain more carbonation when refrigerated than at room temperature?

Explain why pressure affects the solubility of 02 in water, but not the solubility of NaCI in water.

The Henry's law constant for helium gas in water at 30 'C is 3.7 X 10-4 Mjatm and the constant for N2 at 30 'C is 6.0 X 10-4 M/atm. If the two gases are each present at 1.5 atm pressure, calculate the solubility of each gas.

The partial pressure of 02 in air at sea level is 0.21 atm. Using the data in Table 13.2, together with Henry's law, calculate the molar concentration of 02 in the surface water of a mountain lake saturated with air at 20 'C and an atmospheric pressure of 650 torr.

(a) Calculate the mass percentage of Na2S04 in a solution containing 10.6 g Na2S04 in 483 g water. (b) An ore contains 2.86 g of silver per ton of ore. What is the concentration of silver in ppm?

(a) What is the mass percentage of iodine (!2) in a solution containing O.Q35 mol !2 in 115 g of CC14? (b) Seawater contains 0.0079 g Sr2+ per kilogram of water. What is the concentration of Sr2 + measured in ppm?

A solution is made containing 14.6 g of CHsOH in 184 g H20. Calculate (a) the mole fraction of CH30H, (b) the mass percent of CH30H, (c) the molality of CH30H.

A solution is made containing 25.5 g phenol (C6H50H) in 425 g ethanol (C2H50H). Calculate (a) the mole fraction of phenol, (b) the mass percent of phenol, (c) the molality of phenol.

Calculate the molarity of the following aqueous solutions: (a) 0.540 g Mg(N03)z in 250.0 mL of solution, (b) 22.4 g LiC104 3 HzO in 125 mL of solution, (c) 25.0 mL of 3.50 M HN03 diluted to 0.250 L.

Calculate the molality of each of the following solutions: (a) 8.66 g benzene (C6H6) dissolved in 23.6 g carbon tetrachloride (CC4), (b) 4.80 g NaCI dissolved in 0.350 L of water.

(a) What is the molality of a solution formed by dissolving 1 .25 mol ofKCl in 16.0 mol of water? (b) How many grams of sulfur (58) must be dissolved in 100.0 g naphthalene (C10H8) to make a 0.12 m solution?

A sulfuric acid solution containing 571.6 g of H2S04 per liter of solution has a density of 1.329 g/cm3 Calculate (a) the mass percentage, (b) the mole fraction, (c) the molality, (d) the molarity of H2S04 in this solution.

Ascorbic acid (vitamin C, C6H806) is a water-soluble vitamin. A solution containing 80.5 g of ascorbic acid dissolved in 210 g of water has a density of 1.22 g/mL at 55 'C. Calculate (a) the mass percentage, (b) the mole fraction, (c) the molality, (d) the molarity of ascorbic acid in this solution.

The density of acetonitrile (CH3CN) is 0.786 g/mL and the density of methanol (CH30H) is 0.791 g/mL. A solution is made by dissolving 22.5 mL CH30H in 98.7 mL CH3CN. (a) What is the mole fraction of methanol in the solution? (b) What is the molality of the solution? (c) Assuming that the volumes are additive, what is the molarity of CH30H in the solution?

The density of toluene (C7H8) is 0.867 g/mL, and the density of thiophene (C4H4S) is 1.065 g/mL. A solution is made by dissolving 9.08 g of thiophene in 250.0 mL of toluene. (a) Calculate the mole fraction of thiophene in the solution. (b) Calculate the molality of thiophene in the solution. (c) Assuming that the volumes of the solute and solvent are additive, what is the molarity of thiophene in the solution?

Calculate the number of moles of solute present in each of the following aqueous solutions: (a) 600 mL of 0.250 M SrBrz, (b) 86.4 g of 0.180 m KCI, (c) 124.0 g of a solution that is 6.45% glucose (C6H1206) by mass.

Calculate the number of moles of solute present in each of the following solutions: (a) 185 mL of 1.50 M HN03(aq), (b) 50.0 mg of an aqueous solution that is 1.25 m NaCI, (c) 75.0 g of an aqueous solution that is 1.50% sucrose (C 12H22011) by mass.

Describe how you would prepare each of the following aqueous solutions, starting with solid KBr: (a) 0.75 L of 1.5 X 10-2 M KBr, (b) 125 g of 0.180 m KBr, (c) 1.85 L of a solution that is 12.0% KBr by mass (the density of the solution is 1 .10 g/mL), (d) a 0.150 M solution of KBr that contains just enough KBr to precipitate 16.0 g of AgBr from a solution containing 0.480 mol of AgN03.

Commercial aqueous nitric acid has a density of 1.42 g/mL and is 16 M. Calculate the percent HN03 by mass in the solution.

Commercial concentrated aqueous arnrnonia is 28% NH3 by mass and has a density of 0.90 g/mL. What is the molarity of this solution?

Brass is a substitutional alloy consisting of a solution of copper and zinc. A particular sample of red brass consisting of 80.0% Cu and 20.0% Zn by mass has a density of 8750 kgjm3 . (a) What is the molality of Zn in the solid solution? (b) What is the molarity of Zn in the solution?

Caffeine (C8H10N402) is a stimulant found in coffee and tea. If a solution of caffeine in chloroform (CHCl3) as a solvent has a concentration of 0.0750 m, calculate (a) the percent caffeine by mass, (b) the mole fraction of caffeine.

During a typical breathing cycle the C02 concentration in the expired air rises to a peak of 4.6% by volume. Calculate the partial pressure of the C02 at this point, assuming 1 atm pressure. What is the molarity of the C02 in air at this point, assuming a body temperature of 37 C?

Breathing air that contains 4.0% by volume C02 over time causes rapid breathing, throbbing headache, and nausea, among other symptoms. What is the concentration of C02 in such air in terms of (a) mol percentage, (b) molarity, assuming 1 atrn pressure, and a body temperature of 37 C?

List four properties of a solution that depend on the total concentration but not the type of particle or particles present as solute. Write the mathematical expression that describes how each of these properties depends on concentration.

How does increasing the concentration of a nonvolatile solute in water affect the following properties: (a) vapor pressure, (b) freezing point, (c) boiling point; (d) osmotic pressure?

Consider two solutions, one formed by adding 10 g of glucose (C6H1206) to 1 L of water and the other formed by adding 10 g of sucrose (C12H22011) to 1 L of water. Are the vapor pressures over the two solutions the same? Why or why not?

(a) Calculate the vapor pressure of water above a solution prepared by adding 22.5 g of lactose (C12H22011) to 200.0 g of water at 338 K. (Vapor-pressure data for water are given in Appendix B.) (b) Calculate the mass of propylene glycol (C3H802) that must be added to 0.340 kg of water to reduce the vapor pressure by 2.88 torr at 40 oc.

(a) Calculate the vapor pressure of water above a solution prepared by dissolving 32.5 g of glycerin (C3H803) in 125 g of water at 343 K. (The vapor pressure of water is given in Appendix B.) (b) Calculate the mass of ethylene glycol (C2H602) that must be added to 1.00 kg of ethanol (C2H50H) to reduce its vapor pressure by 10.0 torr at 35 oc. The vapor pressure of pure ethanol at 35 oc is 1.00 x 102 torr.

At 63.5 oc the vapor pressure of H20 is 175 torr, and that of ethanol (C2H50H) is 400 torr. A solution is made by mixing equal masses of H20 and C2H50H. (a) What is the mole fraction of ethanol in the solution? (b) Assuming ideal-solution behavior, what is the vapor pressure of the solution at 63.5 C? (c) What is the mole fraction of ethanol in the vapor above the solution?

At 20 oc the vapor pressure of benzene (C6) is 75 torr, and that of toluene (C7H8) is 22 torr. Assume that benzene and toluene form an ideal solution. (a) What is the composition in mole fractions of a solution that has a vapor pressure of 35 torr at 20 C? (b) What is the mole fraction of benzene in the vapor above the solution described in part (a)?

(a) Why does a 0.10 m aqueous solution of NaCl have a higher boiling point than a 0.10 m aqueous solution of C6H1206? (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?

Arrange the following aqueous solutions, each 10% by mass in solute, in order of increasing boiling point: glucose (C6H1206), sucrose (C12H2zOn), sodium nitrate (NaN03).

List the following aqueous solutions in order of increasing boiling point: 0.120 m glucose, 0.050 m LiBr, 0.050 m Zn(N03)z.

List the following aqueous solutions in order of decreasing freezing point: 0.040 m glycerin (C3H803), 0.020 m KBr, 0.030 m phenol (C6H50H).

Using data from Table 13.4, calculate the freezing and boiling points of each of the following solutions: (a) 0.22 m glycerol (C3H803) in ethanol, (b) 0.240 mol of naphthalene (C10H8) in 2.45 mol of chloroform, (c) 2.04 g KBr and 4.82 g glucose (C 1206) in 188 g of water.

How many grams of ethylene glycol (CzH60z) must be added to 1.00 kg of water to produce a solution that freezes at -5.00 C?

What is the freezing point of an aqueous solution that boils at 105.0 C?

What is the osmotic pressure formed by dissolving 44.2 mg of aspirin (C9H804) in 0.358 L of water at 25 C?

Seawater contains 3.4 g of salts for every liter of solution. Assuming that the solute consists entirely of NaCI (over 90% is), calculate the osmotic pressure of seawater at 20 oc.

Adrenaline is the hormone that triggers the release of extra glucose molecules in times of stress or emergency. A solution of 0.64 g of adrenaline in 36.0 g of CCI4 elevates the boiling point by 0.49 oc. Is the molar mass of adrenaline calculated from the boiling point elevation in agreement with the following structural formula?

Laury! alcohol is obtained from coconut oil and is used to make detergents. A solution of 5.00 g of lauryl alcohol in 0.100 kg of benzene freezes at 4.1 C. What is the approximate molar mass of Iaury! alcohol?

Lysozyme is an enzyme that breaks bacterial cell walls. A solution containing 0.150 g of this enzyme in 210 mL of solution has an osmotic pressure of 0.953 torr at 25 oc. What is the molar mass of lysozyme?

A dilute aqueous solution of an organic compound soluble in water is formed by dissolving 2.35 g of the compound in water to form 0.250 L solution. The resulting solution has an osmotic pressure of 0.605 atm at 25 C. Assuming that the organic compound is a nonelectrolyte, what is its molar mass?

The osmotic pressure of a 0.010 M aqueous solution of CaC12 is found to be 0.674 atrn at 25 oc. (a) Calculate the van't Hoff factor, i, for the solution. (b) How would you expect the value of i to change as the solution becomes more concentrated? Explain.

(a) Why is there no colloid in which both the dispersed substance and the dispersing substance are gases? (b) Michael Faraday first prepared ruby-red colloids of gold particles in water that were stable for indefinite times. =(Section 12.6) To the unaided eye these brightly colored colloids are not distinguishable from solutions. How could you determine whether a given colored preparation is a solution or colloid?

(a) Many proteins that remain homogeneously distributed in water have molecular masses in the range of 30,000 amu and larger. In what sense is it appropriate to consider such suspensions to be colloids rather than solutions? Explain. (b) What general name is given to a colloidal dispersion of one liquid in another? What is an emulsifying agent?

Indicate whether each of the following is a hydrophilic or a hydrophobic colloid: (a) butterfat in homogenized milk, (b) hemoglobin in blood, (c) vegetable oil in a salad dressing, (d) colloidal gold particles in water.

Explain how each of the following factors helps determine the stability or instability of a colloidal dispersion: (a) particulate mass, (b) hydrophobic character, (c) charges on colloidal particles.

Colloidal suspensions of proteins, such as a gelatin, can often be caused to separate into two layers by addition of a solution of an electrolyte. Given that protein molecules may carry electrical charges on their outer surface as illustrated in Figure 13.28, what do you believe happens when the electrolyte solution is added?

Explain how (a) a soap such as sodium stearate stabilizes a colloidal dispersion of oil droplets in water; (b) milk curdles upon addition of an acid.

Butylated hydroxytoluene (BHT) has the following molecular structure: Jt is widely used as a preservative in a variety of foods, including dried cereals. Based on its structure, would you expect BHT to be more soluble in water or in hexane (C6H14)? Explain.

A saturated solution of sucrose (C12H22011) is made by dissolving excess table sugar in a flask of water. There are 50 g of undissolved sucrose crystals at the bottom of the flask in contact with the saturated solution. The flask is stoppered and set aside. A year later a single large crystal of mass 50 g is at the bottom of the flask. Explain how this experiment provides evidence for a dynamic equilibrium between the saturated solution and the undissolved solute.

Fish need at least 4 ppm dissolved 02 for survival. (a) What is this concentration in mol/L? (b) What partial pressure of 02 above the water is needed to obtain this concentration at 10 'C? (The Henry's law constant for 02 at this temperature is 1.71 X 10-3 mol/L-atm.)

Glucose makes up about 0.10% by mass of human blood. Calculate the concentration in (a) ppm, (b) molality. What further information would you need to determine the molarity of the solution?

The maximum allowable concentration of lead in drinking water is 9.0 ppb. (a) Calculate the molarity of lead in a 9.0-ppb solution. What assumption did you have to make in your calculation? (b) How many grams of lead are in a swimming pool containing 9.0 ppb lead in 60 m 3 of water?

Acetonitrile (CH3CN) is a polar organic solvent that dissolves a wide range of solutes, including many salts. The densit of a 1.80 M LiBr solution in acetonitrile is 0.826 g/cm . Calculate the concentration of the solution in (a) molality, (b) mole fraction of LiBr, (c) mass percentage of CH3CN.

A "canned heat" product used to warm chafing dishes consists of a homogeneous mixture of ethanol (C2H50H) and paraffin that has an average formula of C24H50. What mass of C2H50H should be added to 620 kg of the paraffin in formulating the mixture if the vapor pressure of ethanol at 35 'C over the mixture is to be 8 torr? The vapor pressure of pure ethanol at 35 'C is 100 torr

Two beakers are placed in a sealed box at 25 'C. One beaker contains 30.0 mL of a 0.050 M aqueous solution of a nonvolatile nonelectrolyte. The other beaker contains 30.0 mL of a 0.035 M aqueous solution of NaCI. The water vapor from the two solutions reaches equilibrium. (a) In which beaker does the solution level rise, and in which one does it fall? (b) What are the volumes in the two beakers when equilibrium is attained, assuming ideal behavior?

A solution contains 0.115 mol H20 and an unknown number of moles of sodium chloride. The vapor pressure of the solution at 30 'C is 25.7 torr. The vapor pressure of pure water at this temperature is 31.8 torr. Calculate the number of moles of sodium chloride in the solution. (Hint: remember that sodium chloride is a strong electrolyte.)

Show that the vapor-pressure reduction, ll.Psolvenv associated with the addition of a nonvolatile solute to a volatile solvent is given by the equation ll.Psolvent = Xsolute X Polvcnt

A car owner who knows no chemistry has to put antifreeze in his car's radiator. The instructions recommend a mixture of 30% ethylene glycol and 70% water. Thinking he will improve his protection he uses pure ethylene glycol. He is saddened to find that the solution does not provide as much protection as he hoped. Why not?

Calculate the freezing point of a 0.100 m aqueous solution of K2S04, (a) ignoring interionic attractions, and (b) taking interionic attractions into consideration by using the van't Hoff factor (Table 13.5).

Carbon disulfide (C) boils at 46.30 oc and has a density of 1.261 g/mL. (a) When 0.250 mol of a nondissociating solute is dissolved in 400.0 mL of CS:u the solution boils at 47.46 oc. What is the molal boiling-point-elevation constant for CS2? (b) When 5.39 g of a nondissociating unknown is dissolved in 50.0 mL of CS;u the solution boils at 47.08 oc. What is the molecular weight of the unknown?

A 40.0% by weight solution of KSCN in water at 20 oc has a density of 1.22 g/mL. (a) What is the mole fraction of KSCN in the solution, and what are the molarity and molality? (b) Given the calculated mole fraction of salt in the solution, comment on the total number of water molecules available to hydrate each anion and cation. What ion pairing (if any) would you expect to find in the solution? Would you expect the colligative properties of such a solution to be those predicted by the formulas given in this chapter? Explain.

A lithium salt used in lubricating grease has the formula LiC.H2n+102. The salt is soluble in water to the extent of 0.036 g per 100 g of water at 25 oc. The osmotic pressure of this solution is found to be 57.1 torr. Assuming that molality and molarity in such a dilute solution are the same and that the lithium salt is completely dissociated in the solution, determine an appropriate value of 11 in the formula for the salt

Fluorocarbons (compounds that contain both carbon and fluorine) were, until recently, used as refrigerants. The compounds listed in the following table are all gases at 25 oc, and their solubilities in water at 25 oc and 1 atm fluorocarbon pressure are given as mass percentages. (a) For each fluorocarbon, calculate the molality of a saturated solution. (b) Explain why the molarity of each of the solutions should be very close numerically to the molality. (c) Based on their molecular structures, account for the differences in solubility of the four fluorocarbons. (d) Calculate the Henry's law constant at 25 oc for CHCIF;u and compare its magnitude to that for N2 (6.8 X 10- 4 moi/L-atm). Can you account for the difference in magnitude? Fluorocarbon CF4 CCIF3 CCI2F2 CHCIF2 Solubility (mass %) 0.0015 0.009 0.028 0.30

At ordinary body temperature (37 C) the solubility of N2 in water in contact with air at ordinary atmospheric pressure (1.0 atm) is 0.015 g/L. Air is approximately 78 mol % N2. Calculate the number of moles of N2 dissolved per liter of blood, which is essentially an aqueous solution. At a depth of 100 ft in water, the pressure is 4.0 atm. What is the solubility of N2 from air in blood at this pressure? If a scuba diver suddenly surfaces from this depth, how many milliliters of N2 gas, in the form of tiny bubbles, are released into the bloodstream from each liter of blood?

Consider the following values for enthalpy of vaporization (kJ/mol) of several organic substances: 0 II H2C..--O...._ CH3C-H 30.4 CH2 28.5 Acetaldehyde Ethylene oxide 0 II CH CH3CCH3 32.0 H2C..-- 2... ._CH2 24.7 Acetone Cyclopropane (a) Use variations in the intermolecular forces operating in these organic liquids to account for their variations in heats of vaporization. (b) How would you expect the solubilities of these substances to vary in hexane as solvent? 1n ethanol? Use intermolecular forces, including hydrogen-bonding interactions where applicable, to explain your responses.

The enthalpies of solution of hydrated salts are generally more positive than those of anhydrous materials. For example, tl.H of solution for KOH is -57.3 kJ/mol whereas that for KOH H20 is -14.6 kJ/mol. Similarly, tl.Hsoln for NaCI04 is + 13.8 k)/mol, whereas that for NaCI04 H20 is +22.5 kJ/mol. Use the enthalpy contributions to the solution process depicted in Figure 13.4 to explain this effect.

A textbook on chemical thermodynamics states, "The heat of solution represents the difference between the lattice energy of the crystalline solid and the solvation energy of the gaseous ions." (a) Draw a simple energy diagram to illustrate this statement. (b) A salt such as NaBr is insoluble in most polar nonaqueous solvents such as acetonitrile (CH3CN) or nitromethane (CH3N02), but salts of large cations, such as tetramethylammonium bromide [(CH3)4NBr], are generally more soluble. Use the thermochemical cycle you drew in part (a) and the factors that determine the lattice energy (Section 8.2) to explain this fact.

(a) A sample of hydrogen gas is generated in a closed container by reacting 2.050 g of zinc metal with 15.0 mL of 1.00 M sulfuric acid. Write the balanced equation for the reaction, and calculate the number of moles of hydrogen formed, assuming that the reaction is complete. (b) The volume over the solution is 122 mL. Calculate the partial pressure of the hydrogen gas in this volume at 25 oc, ignoring any solubility of the gas in the solution. (c) The Henry's law constant for hydrogen in water at 25 oc is 7.8 x 10-4 moi/L-atm. Estimate the number of moles of hydrogen gas that remain dissolved in the solution. What fraction of the gas molecules in the system is dissolved in the solution? Was it reasonable to ignore any dissolved hydrogen in part (b)?

Consider the process illustrated in Figure 13.23, the net movement of solvent from the more dilute to the more concentrated solution through the semipermeable membrane. Is there a change in entropy of the system in going from the left to center panels? Explain. (Hint: Imagine that the more dilute solution on the right hand side of the apparatus is pure solvent.)

When 0.55 g of pure benzoic acid (C6H5COOH) is dissolved in 32.0 g of benzene (C6H6), the freezing point of the solution is 0.36 'C lower than the freezing point value of 5.5 'C for the pure solvent. (a) Calculate the molecular weight of benzoic acid in benzene. (b) Use the structure of the solute to account for the observed value:

At 35 'C the vapor pressure of acetone, (CH3)zCO, is 360 torr, and that of chloroform, CHCl3, is 300 torr. Acetone and chloroform can form weak hydrogen bonds between one another as follows: A solution composed of an equal number of moles of acetone and chloroform has a vapor pressure of 250 torr at 35 'C. (a) What would be the vapor pressure of the solution if it exhibited ideal behavior? (b) Use the existence of hydrogen bonds between acetone and chloroform molecules to explain the deviation from ideal behavior. (c) Based on the behavior of the solution, predict whether the mixing of acetone and chloroform is an exothermic (!l.Hsoln < 0) or endothermic (!l.Hsoln > 0) process.