Problem 84
The elemental analysis of an organic solid extracted from gum arabic (a gummy substance used in adhesives, inks, and pharmaceuticals) showed that it contained 40.0 percent \(\mathrm{C}, 6.7\) percent \(\mathrm{H}\), and 53.3 percent \(\mathrm{O}\). A solution of \(0.650 \mathrm{~g}\) of the solid in \(27.8 \mathrm{~g}\) of the solvent diphenyl gave a freezing-point depression of \(1.56^{\circ} \mathrm{C}\). Calculate the molar mass and molecular formula of the solid. \(\left(K_{\mathrm{f}}\right.\) for diphenyl is \(8.00^{\circ} \mathrm{C} / \mathrm{m} .\) )
Problem 86
The molar mass of benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)\) determined by measuring the freezing-point depression in benzene is twice what we would expect for the molecular formula, \(\mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{2} .\) Explain this apparent anomaly.
Problem 87
A solution containing \(0.8330 \mathrm{~g}\) of a polymer of unknown structure in \(170.0 \mathrm{~mL}\) of an organic solvent was found to have an osmotic pressure of \(5.20 \mathrm{mmHg}\) at \(25^{\circ} \mathrm{C}\). Determine the molar mass of the polymer.
Problem 88
A quantity of \(7.480 \mathrm{~g}\) of an organic compound is dissolved in water to make \(300.0 \mathrm{~mL}\) of solution. The solution has an osmotic pressure of \(1.43 \mathrm{~atm}\) at \(27^{\circ} \mathrm{C}\). The analysis of this compound shows that it contains 41.8 percent \(\mathrm{C}, 4.7\) percent \(\mathrm{H}, 37.3\) percent \(\mathrm{O},\) and 16.3 percent \(\mathrm{N}\). Calculate the molecular formula of the compound.
Problem 89
A solution of \(6.85 \mathrm{~g}\) of a carbohydrate in \(100.0 \mathrm{~g}\) of water has a density of \(1.024 \mathrm{~g} / \mathrm{mL}\) and an osmotic pressure of 4.61 atm at \(20.0^{\circ} \mathrm{C}\). Calculate the molar mass of the carbohydrate.
Problem 90
A \(0.036 M\) aqueous nitrous acid \(\left(\mathrm{HNO}_{2}\right)\) solution has an osmotic pressure of 0.93 atm at \(25^{\circ} \mathrm{C}\). Calculate the percent ionization of the acid.
Problem 91
A \(0.100-M\) aqueous solution of the base \(\mathrm{HB}\) has an osmotic pressure of 2.83 atm at \(25^{\circ} \mathrm{C}\). Calculate the percent ionization of the base.
Problem 93
Describe how hydrophilic and hydrophobic colloids are stabilized in water.
Problem 94
Describe and give an everyday example of the Tyndall effect.
Problem 96
Solutions \(\mathrm{A}\) and \(\mathrm{B}\) have osmotic pressures of 2.4 and 4.6 atm, respectively, at a certain temperature. What is the osmotic pressure of a solution prepared by mixing equal volumes of \(\mathrm{A}\) and \(\mathrm{B}\) at the same temperature?
