Chapter 11

Which one of the following aqueous solutions should have the lowest freezing point: \(0.0500 \mathrm{m} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}, 0.0450 \mathrm{m}\) \(\mathrm{NaI},\) or \(0.0125 \mathrm{m} \mathrm{K}_{2} \mathrm{SO}_{4} ?\)

Arrange the following aqueous solutions in order of increasing boiling point: a. \(0.06 m\) FeCl \(_{3}(i=3.4)\) b. \(0.10 m \mathrm{MgCl}_{2}(i=2.7)\) c. \(0.20 \mathrm{m} \mathrm{KCl}(i=1.9)\)

Arrange the following solutions in order of increasing freezing point depression: a. \(0.10 \mathrm{m} \mathrm{MgCl}_{2}\) in water, \(i=2.7, K_{t}=1.86^{\circ} \mathrm{C} / \mathrm{m}\) b. \(0.20 m\) toluene in diethyl ether, \(i=1.00\) \(K_{f}=1.79^{\circ} \mathrm{C} / \mathrm{m}\) c. \(0.20 \mathrm{m}\) cthylenc glycol in ethanol, \(i=1.00\) \(K_{\mathrm{f}}=1.99^{\circ} \mathrm{C} / \mathrm{m}\)

The freezing point of a solution prepared by dissolving 150 mg of caffeine in \(10.0 \mathrm{g}\) of camphor is lower by \(3.07^{\circ} \mathrm{C}\) than that of pure camphor \(\left(K_{f}=39.7^{\circ} \mathrm{C} / \mathrm{m}\right)\) What is the molar mass of caffeine? Elemental analysis of caffeine yields the following results: \(49.49 \%\) C, \(5.15 \% \mathrm{H}\) \(28.8796 \mathrm{N},\) and the remainder is \(\mathrm{O} .\) What is the molecular formula of caffeine?

One of the ingredients in the Native American stomachache remedy derived from common chokecherry is caffeic acid. a. Combustion of 100 mg of caffeic acid yielded \(220 \mathrm{mg}\) \(\mathrm{CO}_{2}\) and \(40.3 \mathrm{mg} \mathrm{H}_{2} \mathrm{O} .\) Determine the empirical formula of caffeic acid. b. \(A\) solution of \(0.272 \mathrm{g}\) caffeic acid in \(10.0 \mathrm{g}\) carbon tetrachloride causes the freezing point of the solution to decrease by \(4.47^{\circ} \mathrm{C} .\) Given that \(K_{\mathrm{f}}\) for \(\mathrm{CCl}_{4}\) is \(29.8^{\circ} \mathrm{C} / \mathrm{m}\) and that caffeic acid is a nonelectrolyte, calculate the molar mass and molecular formula of caffeic acid.

The values of \(k_{\mathrm{H}}\) for \(\mathrm{NO}\) and \(\mathrm{CO}\) gas in water at \(20^{\circ} \mathrm{C}\) are \(1.4 \times 10^{-3} \mathrm{M} / \mathrm{atm}\) and \(7.4 \times 10^{-3} \mathrm{M} / \mathrm{atm},\) respectively. Why is CO more soluble in water?

Air is primarily a mixture of nitrogen and oxygen. Is the Henry's law constant for the solubility of air in water the sum of \(k_{\mathrm{H}}\) for \(\mathrm{N}_{2}\) and \(k_{\mathrm{H}}\) for \(\mathrm{O}_{2}\) ? Explain why or why not.

Arterial blood contains about \(0.25 \mathrm{g}\) of oxygen per liter at \(37^{\circ} \mathrm{C}\) and standard atmospheric pressure. What is the Henry's law constant, in \(\operatorname{mol} /(\mathrm{L} \cdot \mathrm{atm}),\) for \(\mathrm{O}_{2}\) dissolution in blood at \(37^{\circ} \mathrm{C} ?\)

Nitrous oxide, \(\mathrm{N}_{2} \mathrm{O},\) is used in dental clinics as an anesthetic. The solubility of \(\mathrm{N}_{2} \mathrm{O}\) in water is \(1.1 \mathrm{g} / \mathrm{L}\) at an atmospheric pressure of 1 atm and a temperature of \(20^{\circ} \mathrm{C}\) a. Calculate the Henry's law constant of \(\mathrm{N}_{2} \mathrm{O}\) at \(20^{\circ} \mathrm{C}\). b. Compare the value for \(k_{\mathrm{H}}\) for \(\mathrm{N}_{2} \mathrm{O}\) with the value for \(\mathrm{O}_{2}\) in Table \(11.1 .\) Why are they different?

Melting Ice \(\mathrm{CaCl}_{2}\) is used to melt ice on sidewalks. Could \(\mathrm{CaCl}_{2}\) melt ice at \(-20^{\circ} \mathrm{C} ?\) Assume that the solubility of \(\mathrm{CaCl}_{2}\) at this temperature is \(70.1 \mathrm{g} \mathrm{CaCl}_{2} / 100.0 \mathrm{g}\) of \(\mathrm{H}_{2} \mathrm{O}\) and that the van 't Hoff factor for a saturated solution of \(\mathrm{CaCl}_{2}\) is 2.5.

Making Ice Cream A mixture of table salt and ice is used to chill the contents of hand-operated ice-cream makers. What is the melting point of a mixture of 2.00 Ib of \(\mathrm{NaCl}\) and 12.00 lb of ice if exactly half of the ice melts? Assume that all the NaCl dissolves in the melted ice and that the van 't Hoff factor for the resulting solution is 1.44.

Eugenol is one of the compounds responsible for the flavor of cloves. A 111 mg sample of eugenol is dissolved in \(1.00 \mathrm{g}\) of chloroform \(\left(K_{\mathrm{b}}=3.63^{\circ} \mathrm{C} / \mathrm{m}\right)\) increasing the boiling point of chloroform by \(2.45^{\circ} \mathrm{C}\) Calculate eugenol's molar mass. Eugenol is \(73.17 \% \mathrm{C}\) \(7.32 \% \mathrm{H},\) and \(19.51 \% \mathrm{O}\) by mass. What is the molecular formula of eugenol?

Suppose \(100.0 \mathrm{mL}\) of \(2.50 \mathrm{m} M \mathrm{NaCl}\) is mixed with \(80.0 \mathrm{mL}\) of \(3.60 \mathrm{mM} \mathrm{MgCl}_{2}\) at \(20^{\circ} \mathrm{C} .\) Calculate the osmotic pressure of each starting solution and that of the mixture, assuming that the volumes are additive and that both salts dissociate completely into their component ions.

A solution of 7.50 mg of a small protein in \(5.00 \mathrm{mL}\) aqueous solution has an osmotic pressure of 6.50 torr at \(23.1^{\circ} \mathrm{C} .\) What is the molar mass of the protein?

Xanthotoxin is a natural product extracted from the fruits of Heracleum persicum that seems to have some success in treating a skin discase known as psoriasis. a. Combustion of \(0.0100 \mathrm{g}\) of xanthotoxin in excess oxygen yielded \(0.0244 \mathrm{g} \mathrm{CO}_{2}\) and \(0.00333 \mathrm{g} \mathrm{H}_{2} \mathrm{O}\) Calculate the empirical formula of xanthotoxin. b. A solution of \(0.250 \mathrm{g}\) xanthotoxin in \(10.0 \mathrm{g}\) carbon tetrachloride causes the freezing point of the solution to decrease by \(3.46^{\circ} \mathrm{C} .\) Given that \(K_{f}\) for \(\mathrm{CCl}_{4}\) is \(29.8^{\circ} \mathrm{C} / \mathrm{m}\) and that xanthotoxin is a nonelectrolyte, calculate the molar mass and molecular formula of xanthotoxin.