Problem 97
Acetic acid is a polar molecule and can form hydrogen bonds with water molecules. Therefore, it has a high solubility in water. Yet acetic acid is also soluble in benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\), a nonpolar solvent that lacks the ability to form hydrogen bonds. A solution of \(3.8 \mathrm{~g}\) of \(\mathrm{CH}_{3} \mathrm{COOH}\) in \(80 \mathrm{~g} \mathrm{C}_{6} \mathrm{H}_{6}\) has a freezing point of \(3.5^{\circ} \mathrm{C}\). Calculate the molar mass of the solute, and suggest what its structure might be. (Hint: Acetic acid molecules can form hydrogen bonds between themselves.)
Problem 98
A 2.6-L sample of water contains \(192 \mu \mathrm{g}\) of lead. Does this concentration of lead exceed the safety limit of 0.050 ppm of lead per liter of drinking water?
Problem 99
Why are ice cubes (e.g., those you see in the trays in the freezer of a refrigerator) cloudy inside?
Problem 100
Two liquids A and B have vapor pressures of 76 and \(132 \mathrm{mmHg},\) respectively, at \(25^{\circ} \mathrm{C}\). What is the total vapor pressure of the ideal solution made up of (a) \(1.00 \mathrm{~mol}\) of \(\mathrm{A}\) and \(1.00 \mathrm{~mol}\) of \(\mathrm{B}\) and (b) \(2.00 \mathrm{~mol}\) of \(\mathrm{A}\) and \(5.00 \mathrm{~mol}\) of \(\mathrm{B}\) ?
Problem 101
Determine the van't Hoff factor of \(\mathrm{Na}_{3} \mathrm{PO}_{4}\) in a \(0.40-\mathrm{m}\) solution whose freezing point is \(-2.6^{\circ} \mathrm{C}\).
Problem 103
Predict whether vitamin \(\mathrm{B}_{6}\), also known as pyridoxine, is water- soluble or fat-soluble.
Problem 105
Predict whether vitamin A is water-soluble or fat-soluble.
Problem 107
Explain why reverse osmosis is (theoretically) more desirable as a desalination method than distillation or freezing. What minimum pressure must be applied to seawater at \(25^{\circ} \mathrm{C}\) for reverse osmosis to occur? (Treat seawater as a \(0.70 M \mathrm{NaCl}\) solution.)
Problem 109
How does each of the following affect the solubility of an ionic compound: (a) lattice energy, (b) solvent (polar versus nonpolar), (c) enthalpies of hydration of cation and anion?
Problem 111
The concentration of commercially available concentrated nitric acid is 70.0 percent by mass, or \(15.9 M .\) Calculate the density and the molality of the solution.
