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- You take a sample of water that is at room temperature and in contact with air and put it under a vacuum. Right away, you see bubbles leave the water, but after a little while, the bubbles stop. As you keep applying the vacuum, more bubbles appear. A friend tells you that the first bubbles were water vapor, and that the low pressure had reduced the boiling point of water, causing the water to boil. Another friend tells you that the first bubbles were gas molecules from the air (oxygen, nitrogen, and so forth) that were dissolved in the water. Which friend is most likely to be correct? What, then, is responsible for the second batch of bubbles? [Section 13.4]
Problem 8
Problem 9b
The figure shows two identical volumetric flasks containing the same solution at two temperatures. (b) Does the molality of the solution change with the change in temperature? [Section 13.4]
Problem 10b
This portion of a phase diagram shows the vapor–pressure curves of a volatile solvent and of a solution of that solvent containing a nonvolatile solute. (b) What are the normal boiling points of the solvent and the solution? [Section 13.5]
Problem 11
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]
Problem 12
The diagrams shown represent an emulsion, a true solution, and a liquid crystal. The colored balls represent different liquid molecules. Which diagram corresponds to which type of mixture? [Section 13.6]
- Indicate whether each statement is true or false: (a) A solute will dissolve in a solvent if solute–solute interactions are weaker than solute–solvent interactions. (b) In making a solution, the enthalpy of mixing is always a positive number. (c) An increase in entropy favors mixing.
Problem 13
- Indicate whether each statement is true or false: (a) NaCl dissolves in water but not in benzene (C6H6) because benzene is denser than water. (b) NaCl dissolves in water but not in benzene because water has a large dipole moment and benzene has zero dipole moment. (c) NaCl dissolves in water but not in benzene because the water–ion interactions are stronger than benzene–ion interactions.
Problem 14
Problem 15a
Indicate the type of solute–solvent interaction that should be most important in each of the following solutions: a. CCl4 in benzene (C6H6),
Problem 15b
Indicate the type of solute–solvent interaction that should be most important in each of the following solutions: b. methanol (CH3OH) in water,
Problem 15c
Indicate the type of solute–solvent interaction that should be most important in each of the following solutions: c. KBr in water,
Problem 15d
Indicate the type of solute–solvent interaction that should be most important in each of the following solutions: d. HCl in acetonitrile (CH3CN).
Problem 16a
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) KCl in water
Problem 16b
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: (b) CH2Cl2 in benzene (C6H6)
Problem 16c
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: (c) methanol (CH3OH) in water
Problem 17b
An ionic compound has a very negative ∆Hsoln in water (b) Which term would you expect to be the largest negative number: ∆Hsolvent, ∆Hsolute, or ∆Hmix?
Problem 18a
When ammonium chloride dissolves in water, the solution becomes colder. (a) Is the solution process exothermic or endothermic?
Problem 18b
When ammonium chloride dissolves in water, the solution becomes colder. (b) Why does the solution form?
- (a) In Equation 13.1, which of the enthalpy terms for dissolving an ionic solid would correspond to the lattice energy? (b) Which energy term in this equation is always exothermic?
Problem 19
Problem 20
For the dissolution of LiCl in water, ∆Hsoln = -37 kJ/mol. Which term would you expect to be the largest negative number: ∆Hsolvent, ∆Hsolute, or ∆Hmix?
Problem 21a
Two nonpolar organic liquids, hexane (C6H14) and heptane (C7H16), are mixed. (a) Do you expect ∆Hsoln to be a large positive number, a large negative number, or close to zero? Explain.
Problem 21b
Two nonpolar organic liquids, hexane (C6H14) and heptane (C7H16), are mixed. (b) Hexane and heptane are miscible with each other in all proportions. In making a solution of them, is the entropy of the system increased, decreased, or close to zero, compared to the separate pure liquids?
Problem 22
KBr is relatively soluble in water, yet its enthalpy of solution is + 19.8 kJ/mol. Which of the following statements provides the best explanation for this behavior? (a) Potassium salts are always soluble in water. (b) The entropy of mixing must be unfavorable. (c) The enthalpy of mixing must be small compared to the enthalpies for breaking up water–water interactions and K–Br ionic interactions. (d) KBr has a high molar mass compared to other salts like NaCl.
- The solubility of Cr1NO323 # 9 H2O in water is 208 g per 100 g of water at 15 °C. A solution of Cr1NO323 # 9 H2O in water at 35 °C is formed by dissolving 324 g in 100 g of water. When this solution is slowly cooled to 15 °C, no precipitate forms. (b) You take a metal spatula and scratch the side of the glass vessel that contains this cooled solution, and crystals start to appear. What has just happened?
Problem 23
Problem 25c
By referring to Figure 13.15, determine whether the addition of 40.0 g of each of the following ionic solids to 100 g of water at 40 °C will lead to a saturated solution:(c) K2Cr2O7
Problem 25d
By referring to Figure 13.15, determine whether the addition of 40.0 g of each of the following ionic solids to 100 g of water at 40 °C will lead to a saturated solution: (d) Pb(NO3)2.
Problem 26b
By referring to Figure 13.15, determine the mass of each of the following salts required to form a saturated solution in 250 g of water at 30 °C: (b) Pb(NO3)2,
Problem 26c
By referring to Figure 13.15, determine the mass of each of the following salts required to form a saturated solution in 250 g of water at 30 °C: (c) Ce2(SO4)3.
- Consider water and glycerol, CH2(OH)CH(OH)CH2OH. (b) List the intermolecular attractions that occur between a water molecule and a glycerol molecule.
Problem 27
Problem 28
Oil and water are immiscible. Which is the most likely reason? (a) Oil molecules are denser than water. (b) Oil molecules are composed mostly of carbon and hydrogen. (c) Oil molecules have higher molar masses than water. (d) Oil molecules have higher vapor pressures than water. (e) Oil molecules have higher boiling points than water.
- Common laboratory solvents include acetone (CH3COCH3), methanol (CH3OH), toluene (C6H5CH3), and water. Which of these is the best solvent for nonpolar solutes?
Problem 29