Problem 69
Both \(\mathrm{NaCl}\) and \(\mathrm{CaCl}_{2}\) are used to melt ice on roads and sidewalks in winter. What advantages do these substances have over sucrose or urea in lowering the freezing point of water?
Problem 70
A 0.86 percent by mass solution of \(\mathrm{NaCl}\) is called "physiological saline" because its osmotic pressure is equal to that of the solution in blood cells. Calculate the osmotic pressure of this solution at normal body temperature \(\left(37^{\circ} \mathrm{C}\right) .\) Note that the density of the saline solution is \(1.005 \mathrm{~g} / \mathrm{mL}\).
Problem 71
The osmotic pressure of \(0.010-M\) solutions of \(\mathrm{CaCl}_{2}\) and urea at \(25^{\circ} \mathrm{C}\) are 0.605 and 0.245 atm, respectively. Calculate the van't Hoff factor for the \(\mathrm{CaCl}_{2}\) solution.
Problem 75
Which of the following aqueous solutions has (a) the higher boiling point, (b) the higher freezing point, and (c) the lower vapor pressure: \(0.35 \mathrm{~m} \mathrm{CaCl}_{2}\) or \(0.90 \mathrm{~m}\) urea? Explain. Assume complete dissociation.
Problem 76
Consider two aqueous solutions, one of sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) and the other of nitric acid \(\left(\mathrm{HNO}_{3}\right) .\) Both solutions freeze at \(-1.5^{\circ} \mathrm{C}\). What other properties do these solutions have in common?
Problem 77
Arrange the following solutions in order of decreasing freezing point: \(0.10 \mathrm{~m} \mathrm{Na}_{3} \mathrm{PO}_{4}, 0.35 \mathrm{~m} \mathrm{NaCl}, 0.20 \mathrm{~m}\) \(\mathrm{MgCl}_{2}, 0.15 \mathrm{~m} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}, 0.15 \mathrm{~m} \mathrm{CH}_{3} \mathrm{COOH}\)
Problem 78
Arrange the following aqueous solutions in order of decreasing freezing point, and explain your reasoning: \(0.50 \mathrm{~m} \mathrm{HCl}, 0.50 \mathrm{~m}\) glucose, \(0.50 \mathrm{~m}\) acetic acid.
Problem 79
Indicate which compound in each of the following pairs is more likely to form ion pairs in water: (a) \(\mathrm{NaCl}\) or \(\mathrm{Na}_{2} \mathrm{SO}_{4},\) (b) \(\mathrm{MgCl}_{2}\) or \(\mathrm{MgSO}_{4},\) (c) \(\mathrm{LiBr}\) or \(\mathrm{KBr}\).
Problem 82
Describe how you would use freezing-point depression and osmotic pressure measurements to determine the molar mass of a compound. Why are boiling-point elevation and vapor-pressure lowering normally not used for this purpose?
Problem 83
Describe how you would use the osmotic pressure to determine the percent ionization of a weak, monoprotic acid.
