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- A solution contains 0.115 mol H2O 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 grams of sodium chloride in the solution. (Hint: Remember that sodium chloride is a strong electrolyte.)
Problem 1
Problem 2b
This figure shows the interaction of a cation with surrounding water molecules. (b) Which of the following explanations accounts for the fact that the ion–solvent interaction is greater for Li+ than for K+? a. Li+ is of lower mass than K+. b. The ionization energy of Li is higher than that for K. c. Li+ has a smaller ionic radius than K+. d. Li has a lower density than K. e. Li reacts with water more slowly than K. [Section 13.1]
Problem 3a,b
Consider two ionic solids, both composed of singly charged ions, that have different lattice energies. (a) Will the solids have the same solubility in water? (b) If not, which solid will be more soluble in water, the one with the larger lattice energy or the one with the smaller lattice energy? Assume that solute–solvent interactions are the same for both solids. [Section 13.1]
- Which two statements about gas mixtures are true? [Section 13.1] (a) Gases always mix with other gases because the gas particles are too far apart to feel significant intermolecular attractions or repulsions. (b) Just like water and oil don’t mix in the liquid phase, two gases can be immiscible and not mix in the gas phase. (c) If you cool a gaseous mixture, you will liquefy all the gases at the same temperature. (d) Gases mix in all proportions in part because the entropy of the system increases upon doing so.
Problem 4
- 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 8.10 g of thiophene in 250.0 mL of toluene. Assuming that the volumes of the solute and solvent are additive, what is the molarity of thiophene in the solution?
Problem 5
- If you compare the solubilities of the noble gases in water, you find that solubility increases from smallest atomic weight to largest, specifically: Ar < Kr < Xe. Which of the following statements is the best explanation? [Section 13.3] (a) The heavier the gas, the more it sinks to the bottom of the water and leaves room for more gas molecules at the top of the water. (b) The heavier the gas, the more dispersion forces it has, and therefore the more attractive interactions it has with water molecules. (c) The heavier the gas, the more likely it is to hydrogen-bond with water. (d) The heavier the gas, the more likely it is to make a saturated solution in water.
Problem 6
Problem 7
The structures of vitamins E and B6 are shown below. Predict which is more water soluble and which is more fat soluble. [Section 13.3]
- 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
- Soaps consist of compounds such as sodium stearate, CH3(CH2)16COO–Na+, that have both hydrophobic and hydrophilic parts. Consider the hydrocarbon part of sodium stearate to be the “tail” and the charged part to be the “head.” (a) Which part of sodium stearate, head or tail, is more likely to be solvated by water? (b) Grease is a complex mixture of (mostly) hydrophobic compounds. Which part of sodium stearate, head or tail, is most likely to bind to grease? (c) If you have large deposits of grease that you want to wash away with water, you can see that adding sodium stearate will help you produce an emulsion. What intermolecular interactions are responsible for this?
Problem 9
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
Which diagram best represents a liquid–liquid emulsion such as milk? The colored balls represent different liquid molecules. [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 (Section 11.2) that should be most important in each of the following solutions: (a) CCl4 in benzene
Problem 15b
Indicate the type of solute–solvent interaction (Section 11.2) 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 (Section 11.2) that should be most important in each of the following solutions: (c) KBr in water
Problem 15d
Indicate the type of solute–solvent interaction (Section 11.2) 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
- An ionic compound has a very negative ∆Hsoln in water. (a) Would you expect it to be very soluble or nearly insoluble in water?
Problem 17
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?
Problem 18.8
The first stage of treatment at the reverse osmosis plant in Carlsbad, California, is to flow the water through rock, sand, and gravel as shown here. Would this step remove particulate matter? Would this step remove dissolved salts?
[Section 18.4]
- (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.