Chapter 14

A solution is \(4.00 \%\) (by mass) maltose and \(96.00 \%\) water. It freezes at \(-0.229^{\circ} \mathrm{C}.\) (a) Calculate the molar mass of maltose (which is not an ionic compound). (b) The density of the solution is \(1.014 \mathrm{g} / \mathrm{mL}\). Calculate the osmotic pressure of the solution.

A A tree is exactly \(10 \mathrm{m}\) tall. (a) What must be the total molarity of the solutes if sap rises to the top of the tree by osmotic pressure at \(20^{\circ} \mathrm{C}^{2}\) Assume the groundwater outside the tree is pure water and that the density of the sap is \(1.0 \mathrm{g} / \mathrm{mL} .\left(1 \mathrm{mm} \mathrm{Hg}=13.6 \mathrm{mm} \mathrm{H}_{2} \mathrm{O} .\right)\) (b) If the only solute in the sap is sucrose, \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) what is its percent by mass?

A \(2.00 \%\) solution of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in water freezes at \(-0.796^{\circ} \mathrm{C}.\) (a) Calculate the van't Hoff factor, \(i.\) (b) Which of the following best represents sulfuric acid in a dilute aqueous solution: \(\mathrm{H}_{2} \mathrm{SO}_{4}, \mathrm{H}^{+}+\mathrm{HSO}_{4}^{-},\) or \(2 \mathrm{H}^{+}+\mathrm{SO}_{4}^{2-} ?\)

A compound is known to be a potassium halide, KX. If \(4.00 \mathrm{g}\) of the salt is dissolved in exactly \(100 \mathrm{g}\) of water, the solution freezes at \(-1.28^{\circ} \mathrm{C} .\) Identify the halide ion in this formula.

In chemical research we often send newly synthesized compounds to commercial laboratories for analysis. These laboratories determine the weight percent of \(\mathrm{C}\) and \(\mathrm{H}\) by burning the compound and collecting the evolved \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O} .\) They determine the molar mass by measuring the osmotic pressure of a solution of the compound. Calculate the empirical and molecular formulas of a compound, \(\mathrm{C}_{x} \mathrm{H}_{y}\) Cr, given the following information: (a) The compound contains \(73.94 \%\) C and \(8.27 \%\) H; the remainder is chromium. (b) At \(25^{\circ} \mathrm{C},\) the osmotic pressure of a solution containing 5.00 mg of the unknown dissolved in exactly 100 mL of chloroform solution is \(3.17 \mathrm{mm}\) Hg.

If you dissolve equal molar amounts of \(\mathrm{NaCl}\) and \(\mathrm{CaCl}_{2}\) in water, the CaCl, lowers the freezing point of the water almost 1.5 times as much as the NaCl. Why?

Explain why a cucumber shrivels up when it is placed in a concentrated solution of salt.

A 100 -gram sample of sodium chloride (NaCl) is added to \(100 .\) mL of water at \(0^{\circ} \mathrm{C}\). After equilibrium is reached, about \(64 \mathrm{g}\) of solid remains undissolved. Describe the equilibrium that exists in this system at the particulate Tevel.

Which of the following substances is likely to dissolve in water, and which is likely to dissolve in benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right) ?\) (a) \(\mathrm{NaNO}_{3}\) (b) diethyl ether, \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\) (c) naphthalene, \(\mathrm{C}_{10} \mathrm{H}_{8}\) (d) \(\mathrm{NH}_{4} \mathrm{Cl}\)

Account for the fact that alcohols such as methanol \(\left(\mathrm{CH}_{3} \mathrm{OH}\right)\) and ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\) are quite miscible with water, whereas an alcohol with a long-carbon chain, such as octanol \(\left(\mathrm{C}_{8} \mathrm{H}_{17} \mathrm{OH}\right),\) is poorly soluble in water.

Starch contains \(\mathrm{C}-\mathrm{C}, \mathrm{C}-\mathrm{H}, \mathrm{C}-\mathrm{O},\) and \(\mathrm{O}-\mathrm{H}\) bonds. Hydrocarbons have only \(\mathrm{C}-\mathrm{C}\) and \(\mathrm{C}-\mathrm{H}\) bonds. Both starch and hydrocarbons can form colloidal dispersions in water. Which dispersion is classified as hydrophobic? Which is hydrophilic? Explain briefly.

Which substance would have the greater influence on the vapor pressure of water when added to \(1000 .\) g of the liquid: \(10.0 \mathrm{g}\) of sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)\) or \(10.0 \mathrm{g}\) of ethylene glycol \(\left[\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{OH}\right]\) ?

Suppose you have two aqueous solutions separated by a semipermeable membrane. One contains 5.85 g of \(\mathrm{NaCl}\) dissolved in \(100 .\) mL of solution, and the other contains \(8.88 \mathrm{g}\) of \(\mathrm{KNO}_{3}\) dissolved in \(100 . \mathrm{mL}\) of solution. In which direction will solvent flow: from the NaCl solution to the KNO solution, or from KNO to NaCl? Explain briefly.

A protozoan (single-celled animal) that normally lives in the ocean is placed in fresh water. Will it shrivel or burst? Explain briefly.