Chapter 8

What is meant by dynamic equilibrium? How does it differ from static equilibrium?

Suppose that you have collected \(1.0 \mathrm{~L}\) of humid air by passing it slowly through water at \(20^{\circ} \mathrm{C}\) and into a container. Estimate the mass of water vapor in the collected air, assuming that the air is saturated with water. \(\mathrm{Ar} 20^{\circ} \mathrm{C}\), the vapor pressure of water is \(17.5\) Torr.

Which would be the better solvent, water or benzene, for cach of the following: (a) \(\mathrm{KCl}\); (b) \(\mathrm{CCl}_{4}\), (c) \(\mathrm{CH}_{3} \mathrm{COOH}\) ?

Which would be the better solvent, \(\mathrm{H}_{2} \mathrm{O}\) or \(\mathrm{CCl}_{4}\), for each of the following: (a) \(\mathrm{NH}_{5} ;\) (b) \(\mathrm{HCl} ;\) (c) \(\mathrm{I}_{2}\) ?

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

The carbon dioxide gas dissolved in a sample of water in a partially filled, sealed containcr has reached equilibrium with its 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 addition of nitrogen.

The enthalpy of solution for ammonium nitrate in water is positive. (a) Does \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) dissolve endothermically or exothermically? (b) Write the chemical equation for the dissolving process. (c) Which is larger for \(\mathrm{NH}_{4} \mathrm{NO}_{3}\), the lattice enthalpy or the enthalpy of hydration?

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

A \(0.10-\mathrm{g}\) sample of a polymer, dissolved in \(100 \mathrm{~mL}\). of toluene, had an osmotic pressure of \(5.4\) Torr at \(20^{\circ} \mathrm{C}\). What is the molar mass of the polymer?

A solution prepared by adding \(0.50 \mathrm{~g}\) of a polymer to enough toluene (an organic solvent) to make \(200 \mathrm{~mL}\). of solution had an osmotic pressure of \(0.582\) Torr at \(20^{\circ} \mathrm{C}\). What is the molar mass of the polymer?

Hexane, \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\) and cyclohexane \(\left(\mathrm{C}_{6} \mathrm{H}_{12}\right)\) 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: (a) \(0.2 \mathrm{~S} \mathrm{~mol} \mathrm{C}_{6} \mathrm{H}_{14}\) mixed with \(0.65 \mathrm{~mol} \mathrm{C}_{6} \mathrm{H}_{12}\) (b) \(10.0 \mathrm{~g}\) of hexane mixed with \(10.0 \mathrm{~g}\) of cyclohexane.

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) 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) 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 relatively 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 above the liquid; (d) the addition of air to the volume above the liquid.

The normal boiling point of water is \(100^{\circ} \mathrm{C}\). Suppose a cyclonic region (a region of low pressure) moves into the area. State and explain what happens to the boiling point of the water.

(a) Calculate the mass of \(\mathrm{CaCl}_{2}-6 \mathrm{H}_{2} \mathrm{O}\) needed to prepare a \(0.10 \mathrm{~m} \mathrm{CaCl}_{2}(\mathrm{aq})\) solution, using \(2.50 \mathrm{~g}\) of water. (b) What mass of \(\mathrm{NiSO}_{4} \cdot 6 \mathrm{H}_{2} \mathrm{O}\) must be dissolved in \(500 \mathrm{~g}\) of water to produce a \(0.22 \mathrm{~m}\) \(\mathrm{NiSO}_{4}(\mathrm{aq})\) solution?

Explain in thermodynamic terms why a solute raises the boiling point and lowers the freceing point of a solution.

When determining a molar mass from freczingpoint 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 \(1.00 \mathrm{~g} \cdot \mathrm{cm}^{-3}\), but the water was warmer and less dense than assumed. (c) The thermometer was not calibrated accurately, so the temperature of the freering point was actually \(0.5^{\circ} \mathrm{C}\) higher than recorded. (d) The solution was not stirred sufficiently so that not all the solute dissolved.

Suggest a reason why saltwater fish die when they are suddenly transferred to a freshwater aquarium.

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

Describe the procedure of reverse osmosis for the purification of salt water for drinking water.

Diethyl ether, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OC}_{2} \mathrm{H}_{5}\), and ethyl methyl ether, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OCH}_{3}\), form an ideal solution. The vapor pressure of diethyl ether is 185 Torr and that of ethyl methyl ether is 554 Torr at \(0.0^{\circ} \mathrm{C}\). 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 \(0.0^{\circ} \mathrm{C}\) : (a) \(0.75 \mathrm{~mol}\) of diethyl ether mixed with \(0.50 \mathrm{~mol}\) of ethyl methyl ether; (b) \(25.0 \mathrm{~g}\) of diethyl ether mixed with \(35.0 \mathrm{~g}\) of ethyl methyl ether.

Bromomethane, \(\mathrm{CH}_{3} \mathrm{Br}\), and iodomethane, \(\mathrm{CH}_{3} \mathrm{I}\), form an ideal solution. The vapor pressure of bromomethane is 661 Torr and that of iodomethane is 140 Torr at \(0.0^{\circ} \mathrm{C}\). 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 \(0.0^{\circ} \mathrm{C}:\) (a) \(0.33 \mathrm{~mol}\) of bromomethane mixed with \(0.67 \mathrm{~mol}\) of iodomethane; (b) \(35.0 \mathrm{~g}\) of bromomethane mixed with \(35.0 \mathrm{~g}\) of iodomethane.

A new substance is developed in a laboratory and has the following properties: normal melting point, \(83.7^{\circ} \mathrm{C}\); normal boiling point, \(177^{\circ} \mathrm{C}\); triple point,200 Torr and \(38.6^{\circ} \mathrm{C}\). (a) Sketch the approximate phase diagram and label the solid, liquid, and gaseous phases and the solid-liquid, liquid-gas, and solid-gas phase boundaries. (b) Sketch an approximate cooling curve for a sample at constant pressure, beginning at 500 Torr and \(25^{\circ} \mathrm{C}\) and ending at \(200^{\circ} \mathrm{C}\).

The freezing point of a \(5.00 \%\) by mass \(\mathrm{CH}_{3} \mathrm{COOH}\) (aq) solution is \(-1.576^{\circ} \mathrm{C}\). Determine the experimental van't Hoff \(i\) factor for this solution. Account for its value on the basis of your understanding of intermolecular forces.

A \(0.020 \mathrm{M} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(\mathrm{aq})\) solution is separated from a \(0.050 \mathrm{M} \mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2}(\mathrm{aq})\) solution by a semipermeable membrante at \(25^{\circ} \mathrm{C}\). (a) Which solution has the higher osmotic pressure? (b) Which solution becomes more dilute with the passage of \(\mathrm{H}_{2} \mathrm{O}\) molecules through the membrane? (c) To which solution should an external pressure be applied in order to maintain an equilibrium flow of \(\mathrm{H}_{2} \mathrm{O}\) molecules across the membrane? (d) What external pressure (in atm) should be applied in (c)?