Chapter 9

Which would be the better solvent, water or tetrachloromethane, for each of the following substances: (a) \(\mathrm{NH}_{3}\); (b) \(\mathrm{HNO}_{3} ;\) (c) \(\mathrm{N}_{2}\) ?

The following groups are found in some organic molecules. Which are hydrophilic and which are hydrophobic: (a) \(-\mathrm{NH}_{2}\); (b) \(-\mathrm{CH}_{3} ;\) (c) \(-\mathrm{Br} ;\) (d) \(-\mathrm{COOH}\) ?

The following groups are found in some organic molecules. Which are hydrophilic and which are hydrophobic: (a) -OH; (b) \(-\mathrm{CH}_{2} \mathrm{CH}_{3} ;\) (c) \(-\mathrm{CONH}_{2} ;\) (d) \(-\mathrm{Cl}\) ?

The volume of blood in the body of a certain deep-sea diver is about \(6.00 \mathrm{~L}\). Blood cells make up about \(55 \%\) of the blood volume, and the remaining \(45 \%\) is the aqueous solution called plasma. What is the maximum volume of nitrogen measured at \(1.00 \mathrm{~atm}\) and \(37^{\circ} \mathrm{C}\) that could dissolve in the diver's blood plasma at a depth of \(93 \mathrm{~m}\), where the pressure is \(10.0\) atm? (This is the volume that could come out of solution suddenly, causing the painful and dangerous condition called the bends, if the diver were to ascend too quickly.) Assume that Henry's constant for nitrogen at \(37^{\circ} \mathrm{C}\) (body temperature) is \(5.8 \times 10^{-4} \mathrm{~mol} \cdot \mathrm{L}^{-1}\)-atm \({ }^{-1}\).

The carbon dioxide gas dissolved in a sample of water in a partly filled, sealed container has reached equilibrium with irs partial pressure in the air above the solution. Explain what happens to the solubility of the \(\mathrm{CO}_{2}\) if (a) the partial pressure of the \(\mathrm{CO}_{2}\) gas is doubled by the addition of more \(\mathrm{CO}_{2}\); (b) the total pressure of the gas above the liquid is doubled by the addirion of nitrogen.

Lithium sulfate dissolves exothermically in water. (a) Is the enthalpy of solution for \(\mathrm{Li}_{2} \mathrm{SO}_{4}\) positive or negative? (b) Write the chemical equation for the dissolving process. (c) Which is larger for lithium sulfate, the lattice enthalpy or the enthalpy of hydration?

Calculate (a) the molality of \(\mathrm{KOH}\) in a solution prepared from \(4.25 \mathrm{~g}\) of \(\mathrm{KOH}\) and \(55.0 \mathrm{~g}\) of water; (b) the mass (in grams) of ethylene glycol, \(\mathrm{HOC}{\underline{\phantom{xx}}}_{2} \mathrm{H}_{4} \mathrm{OH}\), that should be added to \(0.85 \mathrm{~kg}\) of water to prepare \(0.35 \mathrm{~m} \mathrm{HOC} 2 \mathrm{H}_{4} \mathrm{OH}(\mathrm{aq}) ;\) (c) the molality of an aqueous \(4.12 \%\) by mass \(\mathrm{HCl}\) solution.

Calculate the concentrations of each of the following solutions: (a) the molality of \(13.63 \mathrm{~g}\) of sucrose, \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\), dissolved in \(612 \mathrm{~mL}\) of water; (b) the molality of CsCl in a \(10.00 \%\) by mass aqueous solution; (c) the molality of acetone in an aqueous solution with a mole fraction for acetone of \(0.197 .\)

What is the osmotic pressure at \(20 .{ }^{\circ} \mathrm{C}\) of (a) \(0.010 \mathrm{M}\) complete dissociation of the \(\mathrm{CaCl}_{2}\).

A \(0.40-\mathrm{g}\) sample of a polypeptide dissolved in \(1.0 \mathrm{~L}\) of an aqueous solution at \(27^{\circ} \mathrm{C}\) gave rise to an osmotic pressure of \(3.74\) Torr. What is the molar mass of the polypeptide?

When \(0.10 \mathrm{~g}\) of insulin is dissolved in \(0.200 \mathrm{~L}\) of water, the osmotic pressure is \(2.30\) Torr at \(20 .{ }^{\circ} \mathrm{C}\). What is the molar mass of insulin?

A \(0.20-\mathrm{g}\) sample of a polymer, dissolved in \(0.100 \mathrm{~L}\) of toluene, has an osmotic pressure of \(6.3\) Torr at \(20 .{ }^{\circ} \mathrm{C}\). What is the molar mass of the polymer?

Calculate the osmotic pressure at \(20^{\circ} \mathrm{C}\) of each of the following solutions; assume complete dissociation of ionic compounds: (a) \(3.0 \times 10^{-3} \mathrm{M}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq}) ;\) (b) \(2.0 \times 10^{-3} \mathrm{M}\) \(\mathrm{CaCl}_{2}(\mathrm{aq}) ;\) (c) \(0.010 \mathrm{M} \mathrm{K}_{2} \mathrm{SO}_{4}(\mathrm{aq})\).

Catalase, a liver enzyme, dissolves in warer. A \(10.0-\mathrm{mL}\). solution containing \(0.166 \mathrm{~g}\) of catalase exhibits an osmotic pressure of \(1.2\) Torr at \(20 .{ }^{\circ} \mathrm{C}\). What is the molar mass of catalase? $.

Benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}\), and toluene, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{3}\), form an ideal solution. The vapor pressure of benzene is \(94.6\) Torr and that of toluene is \(29.1\) Torr at \(25^{\circ} \mathrm{C}\). Calculate the vapor pressure of each of the following solutions and the mole fraction of each substance in the vapor phase above those solutions at \(25^{\circ} \mathrm{C}\) : (a) \(1.50 \mathrm{~mol}\) \(\mathrm{C}_{6} \mathrm{H}_{6}\) mixed with \(0.50 \mathrm{~mol} \mathrm{} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{3} ;\) (b) \(15.0 \mathrm{~g}\) of benzene mixed with \(64.3 \mathrm{~g}\) of toluene.

Hexane, \(\mathrm{C}_{6} \mathrm{H}_{14}\), and cyclohexane, \(\mathrm{C}_{6} \mathrm{H}_{12}\), form an ideal solution. The vapor pressure of hexane is 151 Torr and that of cyclohexane is 98 Torr at \(25.0^{\circ} \mathrm{C}\). Calculate the vapor pressure of each of the following solutions and the mole fraction of each substance in the vapor phase above those solutions at \(25^{\circ} \mathrm{C}\) : (a) \(0.25 \mathrm{~mol} \mathrm{} \mathrm{C}_{6} \mathrm{H}_{14}\) mixed with \(0.65 \mathrm{~mol} \mathrm{} \mathrm{C}_{6} \mathrm{H}_{12}\); (b) \(10.0 \mathrm{~g}\) of hexane mixed with \(10.0 \mathrm{~g}\) of cyclohexane.

Distinguish between a foam and a sol. Give at least one example of each.

Distinguish between an emulsion and a gel. Give at least one example of each.

Complete the following statements about the effect of intermolecular forces on the physical properties of a substance. (a) The higher the boiling point of a liquid, the (stronger, weaker) are its intermolecular forces. (b) Substances with strong intermolecular forces have (high, low) vapor pressures. (c) Substances with strong intermolecular forces typically have (high, low) surface tensions. (d) The higher the vapor pressure of a liquid, the (stronger, weaker) are its intermolecular forces. (c) Because nitrogen, \(\mathrm{N}_{2}\), has (strong, weak) intermolecular forces, it has a (high, low) critical temperature. (f) Substances with high vapor pressures have correspondingly (high, low) boiling points. (g) Because water has a high boiling point, it must have (strong, weak) intermolecular forces and a correspondingly (high, low) enthalpy of vaporization.

Hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2}\), is a syrupy liquid with a vapor pressure lower than that of water and a boiling point of \(152^{\circ} \mathrm{C}\). Account for the differences between these properties and those of water.

Explain the effect that an increase in temperature has on each of the following properties: (a) viscosity; (b) surface tension; (c) vapor pressure; (d) evaporation rate.

Explain how the vapor pressure of a liquid is affected by each of the following changes in conditions: (a) an increase in temperature; (b) an increase in surface area of the liquid; (c) an increase in volume abowe the liquid; (d) the addition of air to the volume above the liquid.

You have two beakers: one is filled with tetrachloromethane and the other with water. You also have two compounds, butane \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\right)\) and calcium chloride. (a) In which liquid will butane dissolve? Sketch the local environment of the solute in the solution. (b) In which solvent will calcium chloride dissolve? Sketch the local environment of the solute in the solution.

When a molar mass is determined from freezing-point depression, it is possible to make each of the following errors (among others). In each case, predict whether the error would cause the reported molar mass to be greater or less than the actual molar mass. (a) There was dust on the balance, causing the mass of solute to appear greater than it actually was. (b) The water was measured by volume, assuming a density of \(1.00 \mathrm{~g}-\mathrm{cm}^{-3}\), but the water was warmer and less dense than assumed. (c) The thermometer was not calibrated accurately, and so the temperature of the freezing point was actually \(0.5^{\circ} \mathrm{C}\) higher than recorded. (d) The solution was not stirred sufficiently, and so not all the solute dissolved.

Interpret the following verse from the Coleridge's Rime of the Ancient Mariner: Water, water, every where, And all the boards did shrink, Water, water every where, Nor any drop to drink.

The vapor pressure of phosphoryl chloride difluoride \(\left(\mathrm{OPClF}_{2}\right)\) has been measured as a function of temperature: \begin{tabular}{cc} Temperature (K) & Vapor pressure (Torr) \\ \hline \(190 .\) & \(3.2\) \\ 228 & 68 \\ \(250 .\) & \(240 .\) \\ 273 & 672 \\ \hline \end{tabular} (a) Plot \(\ln P\) against \(T^{-1}\) (this project is best done with the aid of a computer or a graphing calculator that can calculate a leastsquares fit to the data). (b) From the plot (or a linear equation derived from it) in part (a), determine the standard enthalpy of vaporization of \(\mathrm{OPClF}_{2} ;(c)\) the standard entropy of vaporization of \(\mathrm{OPClF}_{2}\); and (d) the normal boiling point of \(\mathrm{OPClF}_{2}\). (c) If the pressure of a sample of \(\mathrm{OPClF}_{2}\) is reduced to 15 Torr, at what temperature will the sample boil?

Consider an apparatus in which \(A\) and B are two \(1.00-\mathrm{L}\) flasks joined by a stopcock \(\mathrm{C}\). The volume of the stopcock is negligible. Initially, \(\mathrm{A}\) and \(\mathrm{B}\) are evacuated, the stopcock \(\mathrm{C}\) is dosed, and \(1.50 \mathrm{~g}\) of diethyl ether, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5}\), is introduced into flask A. The vapor pressure of diethyl ether is 57 Torr at \(-45^{\circ} \mathrm{C}\), 185 Torr at \(0 .{ }^{\circ} \mathrm{C}, 534\) Torr at \(25^{\circ} \mathrm{C}\), and negligible below \(-86^{\circ} \mathrm{C}\). (a) If the stopcock is left closed and the flask is brought to equilibrium at \(-45^{\circ} \mathrm{C}\), what will be the pressure of diethyl ether in flask A? (b) If the temperature is raised to \(25^{\circ} \mathrm{C}\), what will be the pressure of diethyl ether in the flask? (c) If the temperature of the assembly is returned to \(-45^{\circ} \mathrm{C}\) and the stopcock \(\mathrm{C}\) is opened, what will be the pressure of diethyl ether in the apparatus? (d) If flask \(\mathrm{A}\) is maintained at \(-45^{\circ} \mathrm{C}\) and flask B is cooled with liquid nitrogen (boiling point, \(-196^{\circ} \mathrm{C}\) ) with the stopcock open, what changes will take place in the apparatus? Assume ideal behavior.

The combustion analysis of L-carnitine, an organic compound thought to build muscle strengrh, yielded \(52.16 \% \mathrm{C}\), \(9.38 \% \mathrm{H}, 8.69 \% \mathrm{~N}\), and \(29.78 \%\) O. The osmotic pressure of a \(100.00-\mathrm{mL}\) solution of \(0.322 \mathrm{~g}\) of L-carnitine was found to be \(0.501 \mathrm{~atm}\) at \(32^{\circ} \mathrm{C}\). Assuming that L-carnitine does not ionize in methanol, determine (a) the molar mass of 1-carnitine; (b) the molecular formula of L-carnitine.